Endogenous opiates and the placebo effect: a meta-analytic review

Kalium phosphoricum comp. in patients with neurasthenia: a randomized, double-blind, placebo-controlled clinical trial

OBJECTIVE

This Phase IV placebo-controlled clinical trial was designed to demonstrate the efficacy and safety of the product Neurodoron (Kalium phosporicum comp., KPC) in patients with neurasthenia.

METHODS

This monocenter, randomized, double-blind, placebo-controlled, parallel-group clinical trial (registration number: DRKS00003261) was conducted in an outpatient German trial site. Women and men aged 18 and above were randomized to receive either KPC or placebo if they reported typical symptoms of neurasthenia and a severe psychiatric disorder could be excluded. The primary objectives were a reduction in characteristic symptoms of nervous exhaustion and perceived stress as well as improvement in general health status after 6 weeks of treatment.

RESULTS

In total, 204 patients underwent screening, 78 were randomized in each treatment group, and 77 patients each received treatment (intention-to-treat (ITT) population = 154 patients). For none of the primary efficacy variables, an advantage in favor of KPC could be demonstrated in the pre-specified analysis (p-values between 0.505-0.773, Student's t-test). In a post-hoc analysis of intra-individual differences after 6 weeks treatment, a significant advantage of KPC vs. placebo was shown for characteristic symptoms of nervous exhaustion (irritability (p = 0.020); nervousness (p = 0.045), Student's t-test). Adverse event (AE) rates were similar between treatment groups, in both groups six AEs were assessed as causally related to treatment (severity mild or moderate). No AE resulted in discontinuation of treatment.

CONCLUSIONS

Trial treatment was well tolerated with only a few and minor AEs reported, confirming the markedly good safety of KPC. A significant improvement of neurasthenia was seen for the total study population at the end of the treatment period. Superiority of KPC vs. placebo could not be demonstrated with the pre-specified analysis with regards to a sum score of 12 typical symptoms, perceived stress, or general health status. However, the explorative post-hoc analysis revealed that KPC is superior to placebo in the characteristic symptoms irritability and nervousness. KPC could therefore be a beneficial treatment option for symptomatic relief of neurasthenia.

Placebo and nocebo effects and mechanisms associated with pharmacological interventions: an umbrella review

OBJECTIVES

This review aimed to summarise the existing knowledge about placebo and nocebo effects associated with pharmacological interventions and their mechanisms.

DESIGN

Umbrella review, adopting the Assessment of Multiple Systematic Reviews 2 tool for critical appraisal.

DATA SOURCES

MEDLINE/PubMed, Scopus, Web of Science, PsycINFO, Cochrane Central Register of Controlled Trial were searched in September 2022, without any time restriction, for systematic reviews, narrative reviews, original articles. Results were summarised through narrative synthesis, tables, 95% CI.

OUTCOME MEASURES

Mechanisms underlying placebo/nocebo effects and/or their effect sizes.

RESULTS

The databases search identified 372 studies, for a total of 158 312 participants, comprising 41 systematic reviews, 312 narrative reviews and 19 original articles. Seventy-three per cent of the examined systematic reviews were of high quality.Our findings revealed that mechanisms underlying placebo and/or nocebo effects have been characterised, at least in part, for: pain, non-noxious somatic sensation, Parkinson's disease, migraine, sleep disorders, intellectual disability, depression, anxiety, dementia, addiction, gynaecological disorders, attention-deficit hyperactivity disorder, immune and endocrine systems, cardiovascular and respiratory systems, gastrointestinal disorders, skin diseases, influenza and related vaccines, oncology, obesity, physical and cognitive performance. Their magnitude ranged from 0.08 to 2.01 (95% CI 0.37 to 0.89) for placebo effects and from 0.32 to 0.90 (95% CI 0.24 to 1.00) for nocebo effects.

CONCLUSIONS

This study provides a valuable tool for clinicians and researchers, identifying both results ready for clinical practice and gaps to address in the near future.

FUNDING

Università Cattolica del Sacro Cuore, Milan, Italy with the 'Finanziamento Ponte 2022' grant.

PROSPERO REGISTRATION NUMBER

CRD42023392281.

Are acupuncture and dry needling effective in the management of masticatory muscle pain: A network meta‐analysis of randomised clinical trials

BACKGROUND

Several studies have shown that both acupuncture and dry needling are effective in the treatment of musculoskeletal pains. Therefore, the aim of this network meta-analysis (NMA) was to investigate the treatment outcome of acupuncture and dry-needling for masticatory muscle pain (TMD-M) and to compare with active and inactive placebo.

MATERIAL AND METHOD

An electronic search was performed to identify randomised controlled trials (RCTs) published until September 2019, comparing dry-needling, acupuncture, and inactive as well as active placebo in patients with TMD-M. Outcome variables were post-treatment pain intensity, pressure pain threshold (PPT), and maximum mouth opening (MMO). The quality of evidence was rated according to Cochrane's tool for assessing the risk of bias. Mean difference was used to analyse via frequentist NMA using STATA-software.

RESULTS

Both NMA and direct pairwise meta-analysis have shown that there was no difference between active treatment with either acupuncture or dry-needling when compared to active and inactive placebo in patients with TMD-M with respect to pain intensity, and PPT (p > .05). However, there was a significant increase in MMO following dry-needling when compared to the placebo (very low-quality evidence).

CONCLUSION

Despite the short-term positive effect of MMO by dry-needling, this NMA could not show any pain-reducing effect in patients with TMD-M by acupuncture or dry-needling when compared to an active or inactive placebo. Taken together, this NMA indicates that it is the placebo effect that accounts for the majority of the treatment effect of TMD-M, rather than a real therapeutic effect of acupuncture/dry-needling.

Systematic review and meta-analysis of the placebo effect in panic disorder: Implications for research and clinical practice

OBJECTIVE

This review aimed to measure the degree of placebo response in panic disorder.

DATA SOURCES

We searched major databases up to 31 January 2021, for randomized pharmacotherapy trials published in English.

STUDY SELECTION

A total of 43 studies met inclusion criteria to be in the analysis (with 174 separate outcome measurements).

DATA EXTRACTION

Changes in outcome measures from baseline in the placebo group were used to estimate modified Cohen's d effect size.

RESULTS

A total of 43 trials (2392 subjects, 174 outcomes using 27 rating scales) were included in the meta-analysis. Overall placebo effect size was 0.57 (95% confidence interval = [0.50, 0.64]), heterogeneity (I²: 96.3%). Higher placebo effect size was observed among clinician-rated scales compared to patient reports (0.75 vs 0.35) and among general symptom and anxiety scales compared to panic symptoms and depression scales (0.92 and 0.64 vs 0.56 and 0.54, respectively). There was an upward trend in effect size over the publication period (r = 0.02, p = 0.002) that was only significant among clinician-rated scales (r = 0.02, p = 0.011). There was no significant publication bias, Egger's test (p = 0.08).

CONCLUSION

We observed a substantial placebo effect size in panic disorder. This effect was more prominent for some aspects of panic disorder psychopathology than for others and was correlated with the source of the assessment and publication year. This finding has implications both for research design, to address the heterogeneity and diversity in placebo responses, and for clinical practice to ensure optimal quality of care.

SYSTEMATIC REVIEW REGISTRATION NUMBER

PROSPERO, CRD42019125979.

Consideration in Randomized Placebo-Controlled Trial on Neck Pain to Avoid the Placebo Effect in Analgesic Action

Background: In neck pain treatment, many therapies are focused on etiology, while it is well-known that placebo analgesia is also present in these therapies. The specific efficacy for etiology may be underestimated by ignoring their actual placebo effect. In this study, a logistic regression analysis is used to explore the risk factors causing different placebo responses in patients with neck pain among two RCTs. The probability of the placebo effect is predicted based on these risk factors.

Methods: Trial A and Trial B were similarly designed, randomized, double-/single-blind, placebo-controlled trials in patients treating neck pain with Qishe pill or Shi-style manipulation. Both studies set a placebo pill twice a day or traction for every other day as control. For further analyses on the placebo effect in neck pain management, logistic regression was used to assess subgroup-placebo interactions. The odds ratio assessed a significant influence on the placebo effect.

Results: In this pooled analysis, the total number of patients recruited for these two studies was 284, of which 162 patients received placebo treatment (placebo drug or traction for every other day). No statistically significant differences are found at baseline between the participants with placebo effect and non-placebo effect in the gender, age, and disease duration except in VAS and NDI at the initial time. There are numerically more patients with placebo effect in the shorter disease duration subgroup (< 4 months [76%]), higher initial VAS subgroup (>60 mm [90%]), and worse initial NDI subgroup (>24 [72%]) compared with the gender and age subgroup. An ROC curve is established to assess the model-data fit, which shows an area under the curve of 0.755 and a 95% confidence interval of 0.677–0.830. Participants who show placebo effect after 2 weeks have significantly lower VAS scores after 4 weeks, while there is no significant difference in NDI improvement between the two groups after 4 weeks.

Conclusion: Neck pain patients with shorter disease duration are more likely to overscore their pain severity, because of their less experience in pain perception, tolerance, and analgesia expectation.

Intra-articular placebo effect in the treatment of knee osteoarthritis: a survey of the current clinical evidence

Knee osteoarthritis (KOA) is a debilitating disease characterized by chronic pain, stiffness, and decreased mobility. Intra-articular injectable therapies show good clinical efficacy in improving symptoms; however, these therapies and their comparators (intra-articular saline) have been associated with a large underlying placebo effect. We aimed to describe the existing evidence on the challenges, hypotheses, and potential solutions to mitigate the intra-articular placebo effect in clinical trials in KOA. A targeted literature review was conducted by searching Embase, MEDLINE®, and CENTRAL using predefined study selection criteria. All eligible studies identified were extracted for relevant data, and results were narratively summarized. Forty-three studies were included following screening. Challenges associated with the intra-articular placebo effect included its ability to mask the comparative efficacy of active treatments in trials (n = 7 studies), long-lasting effects (up to 6 months; n = 3), and substantial variation of placebo effect sizes across populations (n = 3). Hypotheses for the mechanism of the placebo effect included aspiration of synovial fluid during administration (n = 6) and dilution of inflammatory mediators (n = 2). Factors affecting the placebo effect size were more invasive routes of administration (e.g., injection versus oral; n = 4) and patient expectations (n = 2). Proposed solutions included the suggestion for readers to weigh the relevance of clinical trial evidence against the presence of large underlying placebo effects (n = 9), discontinuation of intra-articular saline as an appropriate placebo (n = 5), and inclusion of 'no treatment' or sham injection as a control (n = 4). The intra-articular placebo effect is a well-documented occurrence in KOA clinical trials, and it is suggested that it be accounted for when designing randomized controlled trials. Awareness and understanding of the intra-articular placebo effect in KOA are required for fair interpretation of clinical trial evidence.

A social affective neuroscience lens on placebo analgesia

Pain is a fundamental experience that promotes survival. In humans, pain stands at the intersection of multiple health crises: chronic pain, the opioid epidemic, and health disparities. The study of placebo analgesia highlights how social, cognitive, and affective processes can directly shape pain, and identifies potential paths for mitigating these crises. This review examines recent progress in the study of placebo analgesia through affective science. It focuses on how placebo effects are shaped by expectations, affect, and the social context surrounding treatment, and discusses neurobiological mechanisms of placebo, highlighting unanswered questions and implications for health. Collaborations between clinicians and social and affective scientists can address outstanding questions and leverage placebo to reduce pain and improve human health.

Physician perspectives on placebo ethics

Clinical use of placebos is controversial among bioethicists. While placebos have been shown to provide benefit for patients with some conditions, offering placebos to patients without disclosing that they are placebos raises ethical concerns, including the concern that this lack of transparency about the nature of placebos amounts to deceiving patients. Some have proposed open-label placebos (OLPs) as an ethically preferable alternative: patients are offered placebos and told that the treatment being offered is a placebo. To contribute to the ongoing discussion about the ethics and feasibility of clinical use of placebos, we conducted focus groups to explore physician attitudes about clinical use of placebos, including non-disclosed and OLPs, and physician attitudes about the underlying ethical issues. We found that while the non-transparency and deceptiveness of offering non-disclosed placebos was a concern for some physicians, their primary focus when considering both non-disclosed and OLPs was identifying and weighing potential harms and benefits to patients. Some participants also felt further research and training in prescribing OLPs would be needed before they would be willing to use them in their practice.

Naltrexone during pain conditioning: A double-blind placebo-controlled experimental trial

Naltrexone reversibly blocks the effects of opioids and has been shown to decrease placebo analgesia. However, it is not clear (1) to what extent naltrexone affects pain modulation in a nontreatment context, for example, in response to pain cues or (2) how naltrexone given prior to pain-cue learning shapes pain responses. In a double-blind procedure prior to pain-cue conditioning, 30 healthy participants were randomized to receive an oral dose of naltrexone (50 mg) or inert pill. During functional magnetic resonance imaging, high and low pain pressures were paired with two different visual cues: a high pain cue and a low pain cue (learning sequence). During a test sequence, medium levels of pressure were used for both cues and the difference in subjective pain ratings following high and low pain cues was calculated. Results showed significant conditioned pain responses across groups (P < .001); however, no significant difference between participants receiving naltrexone or inert pill (P = .193). There was a significant correlation between the difference in high and low pain ratings during the learning sequence and the effect of high and low pain cues during the test sequence (r = .575, P = .002). Functional magnetic resonance imaging analyses revealed no significant difference in brain activation between groups. Here, we demonstrate comparable learning of pain responses in participants treated with naltrexone or inert pill. The results point to the possibility that associative learning, and conditional responding to pain cues, is not dependent on endogenous opioids. Our results, using pain-cue conditioning to create reduced pain responses, contrast previous studies where opioid antagonists significantly reduced the placebo effect in treatment of pain.

Moderators of Improvement From Mindfulness-Based vs Traditional Cognitive Behavioral Therapy for the Treatment of Provoked Vestibulodynia

BACKGROUND AND AIM

The goal was to evaluate the moderators of mindfulness-based cognitive therapy (MBCT) and cognitive behavioral therapy (CBT) to improve dyspareunia, reduce pain catastrophizing, and improve overall sexual function in women with provoked vestibulodynia (PVD). Both treatments effectively reduced self-reported pain, sexual dysfunction, and pain catastrophizing in women with PVD.

METHODS

A total of 130 women with PVD were assigned to CBT or MBCT.

OUTCOMES

Potential moderators included (i) PVD subtype (primary or secondary), (ii) baseline pain intensity, (iii) trait mindfulness, (iv) treatment credibility, (v) relationship duration, and (vi) age. Outcomes were pain intensity, sexual function, and pain catastrophizing at 4 time points: before and after treatment and 6- and 12-month follow-up. Moderation was tested using multilevel models, nesting 4 time points within participants. The interaction of the moderator, time effect, and treatment group was evaluated for significance, and a simple slope analysis of significant interactions was performed.

RESULTS

Pain reduction across 4 time points was the greatest in women who were younger, in relationships of shorter duration, and with greater baseline pain. Treatment credibility moderated pain intensity outcomes (B = 0.305, P < .01) where those with higher treatment credibility ratings (for that particular treatment) improved more in MBCT than CBT. PVD subtype moderated pain catastrophizing (B = 3.150, P < .05). Those with primary PVD improved more in the CBT condition, whereas women with secondary PVD improved more in the MBCT condition. Relationship length moderated sexual function (B = 0.195, P < .01). Women in shorter relationships improved more with MBCT, whereas women in longer relationships improved more on sexual function with CBT. No other tested variables moderated outcomes differentially across both treatment conditions.

CLINICAL IMPLICATIONS

Women who present with high credibility about mindfulness, in shorter relationships, and with secondary PVD might respond better to MBCT whereas those with primary PVD and longer relationships might respond better to CBT.

STRENGTHS & LIMITATIONS

Clinical sample. Half the women who were not sexually active were omitted from analyses of sexual function.

CONCLUSION

Overall, treatment credibility, relationship length, and PVD subtype were found to moderate improvements differently in MBCT and CBT. These findings may assist clinicians in individualizing psychological treatment for women with PVD.

CLINICAL TRIAL REGISTRATION

This clinical trial was registered with clinicaltrials.gov, NCT01704456. Brotto LA, Zdaniuk B, Rietchel L, et al. Moderators of Improvement From Mindfulness-Based vs Traditional Cognitive Behavioral Therapy for the Treatment of Provoked Vestibulodynia. J Sex Med 2020;17:2247-2259.

Placebo Responses Among Men With Erectile Dysfunction Enrolled in Phosphodiesterase 5 Inhibitor Trials: A Systematic Review and Meta-analysis

IMPORTANCE

Placebo responses in the treatment of erectile dysfunction (ED) are poorly described in the literature to date.

OBJECTIVE

To quantify the association of placebo with ED outcomes among men enrolled in placebo-controlled, phosphodiesterase 5 inhibitor (PDE5I) trials.

DATA SOURCES

For this systematic review and meta-analysis, a database search was conducted to identify double-blind, placebo-controlled studies using PDE5Is for the treatment of ED published from January 1, 1998, to December 31, 2018, within MEDLINE, Embase, Cochrane Library, and Web of Science. Only articles published in the English language were included.

STUDY SELECTION

Double-blind, placebo-controlled randomized clinical trials of PDE5Is for ED were included. Studies were excluded if they did not provide distribution measures for statistical analysis. Study selection review assessments were conducted by 2 independent investigators. A total of 2215 studies were identified from the database search, and after review, 63 studies that included 12 564 men were analyzed.

DATA EXTRACTION AND SYNTHESIS

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed in abstracting data and assessing validity. Data were extracted from published reports by 2 independent reviewers. Quality assessment was performed using the Jadad scale. Data were pooled using a random-effects model.

MAIN OUTCOMES AND MEASURES

The main outcome was improvement in the erectile function domain of the International Index of Erectile Function questionnaire in the placebo arm of the included studies. Effect size was reported as bias-corrected standardized mean difference (Hedges g). The hypothesis was formulated before data extraction.

RESULTS

A total of 63 studies that included 12 564 men (mean [SD] age, 55 [7] years; age range, 36-68 years) were included. Erectile function was significantly improved among participants in the placebo arm, with a small to moderate effect size (Hedges g [SE], 0.35 [0.03]; P < .001). Placebo effect size was larger among participants with ED associated with posttraumatic stress disorder (Hedges g [SE], 0.78 [0.32]; P = .02) compared with the overall analysis. No significant difference was found between placebo and PDE5Is for ED after prostate surgery or radiotherapy (Hedges g [SE], 0.30 [0.17]; P = .08).

CONCLUSIONS AND RELEVANCE

In this study, placebo was associated with improvement of ED, especially among men with ED-related posttraumatic stress disorder. No difference was found between placebo and PDE5I among men treated for ED after prostate surgery.

Does Sex/Gender Play a Role in Placebo and Nocebo Effects? Conflicting Evidence From Clinical Trials and Experimental Studies

Sex has been speculated to be a predictor of the placebo and nocebo effect for many years, but whether this holds true or not has rarely been investigated. We utilized a placebo literature database on various aspects of the genuine placebo/nocebo response. In 2015, we had extracted 75 systematic reviews, meta-analyses, and meta-regressions performed in major medical areas (neurology, psychiatry, internal medicine). These meta-analyses were screened for whether sex/gender differences had been noted to contribute to the placebo/nocebo effect: in only 3 such analyses female sex was associated with a higher placebo effect, indicating poor evidence for a contribution of sex to it in RCTs. This was updated with another set of meta-analyses for the current review, but did not change the overall conclusion. The same holds true for 18 meta-analyses investigating adverse event (nocebo) reporting in RCT in the placebo arm of trials. We also screened our database for papers referring to sex/gender and the placebo effect in experimental studies, and identified 28 papers reporting 29 experiments. Their results can be summarized as follows: (a) Despite higher sensitivity of pain in females, placebo analgesia is easier to elicit in males; (b) It appears that conditioning is effective specifically eliciting nocebo effects; (c) Conditioning works specifically well to elicit placebo and nocebo effects in females and with nausea; (d) Verbal suggestions are not sufficient to induce analgesia in women, but work in men. These results will be discussed with respect to the question why nausea and pain may be prone to be responsive to sex/gender differences, while other symptoms are less. Lastly, we will discuss the apparent discrepancy between RCT with low relevance of sex, and higher relevance of sex in specific experimental settings. We argue that the placebo response is predominantly the result of a conditioning (learning) response in females, while in males it predominantly may be generated via (verbal) manipulating of expectancies. In RCT therefore, the net outcome of the intervention may be the same despite different mechanisms generating the placebo effect between the sexes, while in experimental work when both pathways are separated and explicitly explored, such differences may surface.

An Analysis of the Basic Processes of Formation and Change of Placebo Expectations

Placebo effects are the measurable psychological, biological, and behavioral changes that can result from expecting a treatment to be effective. Here we argue that not all expectations are created equally and there is much to learn by clarifying the psychological processes that underlie the expectations that cause placebo effects. It is proposed that the formation and change of placebo expectations can be understood from the standpoint of a general psychological model describing the basic processes of mental change. Specifically, we use the Elaboration Likelihood Model to explain how placebo-relevant variables (e.g., doctor’s lab coat, drug price, number and color of pills, patient’s mood) can work to affect expectations. Clarifying the antecedent processes responsible for placebo expectations leads to new insights regarding placebo effects, including their durability, directionality, and ability to alter subsequent behaviors (e.g., treatment adherence). A key point from our approach is that expectations causing placebo effects can be formed under high or low thought. High-thought expectations should be more likely to resist change, last over time, predict placebo effects better than low-thought expectations, and have a greater likelihood to alter subsequent behaviors. We conclude by describing a variety of theoretical innovations that this new conceptualization raises and suggest novel paths for research and application.

The influence of reward sensitivity, heart rate dynamics and EEG-delta activity on placebo analgesia

Personality traits have been shown to interact with environmental cues to modulate biological responses including treatment responses, and potentially having a role in the formation of placebo effects. Here we used the Reinforcement Sensitivity Theory Personality Questionnaire (RST-PQ) to identify personality traits that predict placebo analgesic responding. Cardiac inter-beat (RR) time series and electroencephalographic (EEG) band oscillations were recorded from healthy women in a cold-pain (Pain) and placebo analgesia (PA) condition. The measures of Hypnotizability, and self-reported ratings of Hypnotic Depth, Motivation, Pain Expectation, Involuntariness in PA responding, Pain and Distress intensity were obtained. Separate principal components factor analyses with varimax rotation were performed on summarized heart rate variability (HRV) measures of time, frequency, nonlinear Complexity, and EEG-band activity. Both analyses yielded a similar three-factor solution including Frequency HRV (factor-1), Complexity HRV dynamics (factor-2), and time HRV & EEG-delta activity (factor-3). Reward Interest sub-trait of the Behavioral Approach System (BAS-RI), Pain Expectation, Involuntariness in PA responding, and Hypnotic Depth were positively associated, whereas negative changes in time-HRV & EEG-delta scores were associated with Pain Reduction. Multiple mediation analyses disclosed that BAS-RI, potentially served by the dopaminergic system, through Involuntariness in PA responding can alter placebo responding to laboratory pain. Our results also show that a linear compound of HR slowing and higher EEG delta activity during PA explains a substantial proportion of the variance in placebo analgesic responses. Future studies should examine the potential role that these individual difference measures may play in patient responsiveness to treatments for clinical pain.

Pain Modulation: From Conditioned Pain Modulation to Placebo and Nocebo Effects in Experimental and Clinical Pain

Accumulating evidence reveal important applications of endogenous pain modulation assessment in healthy controls and in patients in clinical settings, as dysregulations in the balance of pain modulatory circuits may facilitate pain and promote chronification of pain. This article reviews data on pain modulation, focusing on the mechanisms and translational aspects of pain modulation from conditioned pain modulation (CPM) to placebo and nocebo effects in experimental and clinical pain. The specific roles of expectations, learning, neural and neurophysiological mechanisms of the central nervous system are briefly reviewed herein. The interaction between CPM and placebo systems in pain inhibitory pathways is highly relevant in the clinic and in randomized controlled trials yet remains to be clarified. Examples of clinical implications of CPM and its relationship to placebo and nocebo effects are provided. A greater understanding of the role of pain modulation in various pain states can help characterize the manifestation and development of chronic pain and assist in predicting the response to pain-relieving treatments. Placebo and nocebo effects, intrinsic to every treatment, can be used to develop personalized therapeutic approaches that improve clinical outcomes while limiting unwanted effects.

Impairment of opiate-mediated behaviors by the selective TRPV1 antagonist SB366791

Transient receptor potential vanilloid type 1 (TRPV1), the archetypal member of the vanilloid TRP family, was initially identified as the receptor for capsaicin, the pungent ingredient in hot chili peppers. We previously demonstrated that TRPV1 in the dorsal striatum significantly contributes to morphine reward by using the conditioned place preference paradigm in mice; however, it is unknown whether TRPV1 has the same effect in other reward models. In this study, we investigated the role of TRPV1 in morphine reward by using a self-administration paradigm in rats. We found that treatment with a selective TRPV1 antagonist, SB366791, significantly decreased morphine self-administration on a fixed-ratio 1 schedule or a progressive ratio schedule of reinforcement. In addition, treatment with another selective TRPV1 antagonist, AMG9810, not only significantly prevented morphine self-administration but also prevented morphine-induced c-fos expression in the nucleus accumbens. Furthermore, administration of SB366791 decreased an anxiolytic-like effect during the morphine abstinence period. Moreover, treatment with SB366791 significantly decreased morphine-priming reinstatement. Taken together, our findings suggest that blockade of TRPV1 receptors could provide an approach to limiting morphine addiction.

Placebo-related effects: a meta-narrative review of conceptualization, mechanisms and their relevance in rheumatology

For decades in medicine, the placebo effect has been conceptualized as a subjective psychological effect associated with an inert substance and considered to be a nuisance noise in the assessment of therapeutic effects in clinical trials. However, research on placebo has undergone substantial developments since the mid-1980s in several fields of knowledge (including methodology, psychology and neurosciences) that challenge this traditional view. Using a meta-narrative approach, this review of conceptualizations, determinants, mechanisms and models of placebo effects shows that placebo effects are genuine biopsychosocial phenomena strongly affected by context and factors surrounding the patient and treatments. Psychological experiments and neurobiological and neuroimaging studies have identified various types of placebo responses, driven by different mechanisms (especially but not only expectation and conditioning) and associated with different chemical, structural and functional features. Insights into the mechanisms involved in placebo responses have led to opportunities for ethical enhancements of these mechanisms in clinical practice, notably by improving the patient-doctor interaction and refining the therapeutic ritual. These developments should be carefully considered in rheumatology settings, in which placebo effects are both prevalent and significant, with the potential to improve patient care.

Set and setting, psychedelics and the placebo response: An extra-pharmacological perspective on psychopharmacology

Placebo response theory and set and setting theory are two fields which examine how non-biological factors shape the response to therapy. Both consider factors such as expectancy, preparation and beliefs to be crucial for understanding the extra-pharmacological processes which shape the response to drugs. Yet there are also fundamental differences between the two theories. Set and setting concerns itself with response to psychoactive drugs only; placebo theory relates to all therapeutic interventions. Placebo theory is aimed at medical professionals; set and setting theory is aimed at professionals and drug users alike. Placebo theory is primarily descriptive, describing how placebo acts; set and setting theory is primarily prescriptive, educating therapists and users on how to control and optimize the effects of drugs. This paper examines how placebo theory and set and setting theory can complement and benefit each other, broadening our understanding of how non-biological factors shape response to drugs and other treatment interventions.

Effect of expectation on pain assessment of lower- and higher-intensity stimuli

BACKGROUND AND AIMS

Pain modulation via expectation is a well-documented phenomenon. So far it has been shown that expectations about effectiveness of a certain treatment enhance the effectiveness of different analgesics and of drug-free pain treatments. Also, studies demonstrate that people assess same-intensity stimuli differently, depending on the experimentally induced expectations regarding the characteristics of the stimuli. Prolonged effect of expectation on pain perception and possible symmetry in conditions of lower- and higher-intensity stimuli is yet to be studied. Aim of this study is to determine the effect of expectation on the perception of pain experimentally induced by the series of higher- and lower-intensity stimuli.

METHODS

192 healthy participants were assigned to four experimental groups differing by expectations regarding the intensity of painful stimuli series. Expectations of two groups were congruent with actual stimuli; one group expected and received lower-intensity stimuli and the other expected and received higher-intensity stimuli. Expectations of the remaining two groups were not congruent with actual stimuli; one group expected higher-intensity stimuli, but actually received lower-intensity stimuli while the other group expected lower-intensity stimuli, but in fact received higher-intensity ones. Each group received a series of 24 varied-intensity electrical stimuli rated by the participants on a 30° intensity scale.

RESULTS

Expectation manipulation had statistically significant effect on pain intensity assessment. When expecting lower-intensity stimuli, the participants underestimated pain intensity and when expecting higher-intensity stimuli, they overestimated pain intensity. The effect size of expectations upon pain intensity assessment was equal for both lower- and higher-intensity stimuli.

CONCLUSION

The obtained results imply that expectation manipulation can achieve the desired effect of decreasing or increasing both slight and more severe pain for a longer period of time. Manipulation via expectation before the stimuli series was proven to be effective for pain modulation in the entire series of stimuli which lasted around 10min. The results suggest a potential benefit of manipulating expectations to alleviate emerging pain, since the obtained effects are moderate to large.

IMPLICATIONS

It seems that expectation effect is strong enough to "overcome" even the direct effect of stimulus intensity (at least in the low to moderate intensity range), which suggests potential benefits of verbal instructions even in rather painful stimuli.

The Role of Descending Modulation in Manual Therapy and Its Analgesic Implications: A Narrative Review

Manual therapy has long been a component of physical rehabilitation programs, especially to treat those in pain. The mechanisms of manual therapy, however, are not fully understood, and it has been suggested that its pain modulatory effects are of neurophysiological origin and may be mediated by the descending modulatory circuit. Therefore, the purpose of this review is to examine the neurophysiological response to different types of manual therapy, in order to better understand the neurophysiological mechanisms behind each therapy's analgesic effects. It is concluded that different forms of manual therapy elicit analgesic effects via different mechanisms, and nearly all therapies appear to be at least partially mediated by descending modulation. Additionally, future avenues of mechanistic research pertaining to manual therapy are discussed.

Placebo Responses in Genetically Determined Intellectual Disability: A Meta-Analysis

Background

Genetically determined Intellectual Disability (ID) is an intractable condition that involves severe impairment of mental abilities such as learning, reasoning and predicting the future. As of today, little is known about the placebo response in patients with ID.

Objective

To determine if placebo response exists in patients with genetically determined ID.

Data sources and Study selection

We searched Medline/PubMed, EMBASE, CENTRAL and PsycINFO to find all placebo-controlled double-blind randomized clinical trials (RCTs) in patients with genetically determined ID, published up to April 2013, focusing on core ID symptoms.

Data extraction and synthesis

Two investigators extracted outcome data independently.

Main outcomes and measures

Bias-corrected standardized mean difference (Hedge’s g) was computed for each outcome measure, using the Comprehensive Meta-Analysis software. A priori defined patient sub-groups were analyzed using a mixed-effect model. The relationship between pre-defined continuous variable moderators (age, IQ, year of publication and trial duration) and effect size was analyzed using meta-regression

Results

Twenty-two placebo-controlled double-blind RCTs met the inclusion criteria (n = 721, mean age = 17.1 years, 62% men, mean trial duration = 35 weeks). There was a significant overall placebo response from pre- to post-treatment in patients with ID (g = 0.468, p = 0.002), both for “subjective outcomes” (a third-person’s evaluation of the patient) (g = 0.563, p = 0.022) and “objective outcomes” (direct evaluation of the patient’s abilities) (g = 0.434, p = 0.036). Individuals with higher IQ had higher response to placebo (p = 0.02) and no placebo response was observed in ID patients with comorbid dementia. A significant effect of age (p = 0.02) was found, indicating higher placebo responses in treatment of younger patients.

Conclusions and relevance

Results suggest that patients with genetically determined ID improve in the placebo arm of RCTs. Several mechanisms may contribute to placebo effects in ID, including expectancy, implicit learning and “placebo-by-proxy” induced by clinicians/family members. As the condition is refractory, there is little risk that improvements are explained by spontaneous remission. While new avenues for treatment of genetically determined ID are emerging, our results demonstrate how contextual factors can affect clinical outcomes and emphasize the importance of being vigilant on the role of placebos when testing novel treatments in ID.

Pregabalin and placebo responders show different effects on central pain processing in chronic pancreatitis patients

BACKGROUND

Pain control in chronic pancreatitis is a major challenge; the mechanisms behind analgesic treatment are poorly understood. This study aims to investigate the differences in pain sensitivity and modulation in chronic pancreatitis patients, based on their clinical response (responders vs nonresponders) to placebo or pregabalin treatment.

METHODS

This study was part of a randomized, double-blind, placebo-controlled trial evaluating the analgesic effects of pregabalin and placebo in chronic pancreatitis. Post hoc, patients were assigned to one of four groups, ie, responders and nonresponders to pregabalin (n=16; n=15) or placebo (n=12; n=17) treatment. Responders were defined as patients with >30% pain reduction after 3 weeks of treatment. We measured change in pain sensitivity before and after the treatment using electric pain detection thresholds (ePDT) in dermatomes C5 (generalized effects) and Ventral T10 (segmental effects). Descending endogenous pain modulation was quantified via conditioned pain modulation (CPM) paradigm.

RESULTS

Sixty patients were analyzed in a per-protocol analysis. ePDT change in C5 was significant vs baseline and greater in pregabalin (1.3 mA) vs placebo responders (-0.1 mA; P=0.015). This was not so for ePDT in Ventral T10. CPM increased more in pregabalin (9%) vs placebo responders (-17%; P<0.001). CPM changed significantly vs baseline only for pregabalin responders (P=0.006).

CONCLUSION

This hypothesis-generating study provides the first evidence that pain relief with pregabalin is associated with anti-hyperalgesic effects and increased endogenous inhibitory modulation. No such effects were observed in patients experiencing pain relief with the placebo treatment. The mechanisms underlying analgesic response to placebo vs drug treatments are different and, together with their interactions, deserve further study.

A conjugate vaccine attenuates morphine- and heroin-induced behavior in rats

BACKGROUND

Currently approved medications for opioid addiction have shown clinical efficacy, but undesired side effects, dependence induced by the medications themselves, and low treatment compliance necessitate the need for novel therapies.

METHODS

A novel morphine-keyhole limpet hemocyanin conjugate vaccine was synthesized with 6-glutarylmorphine as the hapten and a lengthened linker of 6 carbon atoms. The titer and specificity of the triggered antibody were assessed by enzyme-linked immunosorbent assay. The effects of the vaccine on the morphine-induced elevation of dopamine levels in the nucleus accumbens were determined by high-performance liquid chromatography. The effects of the vaccine on morphine-induced locomotor sensitization and heroin-primed reinstatement of heroin self-administration were also assessed.

RESULTS

After subcutaneous administration in rats, the vaccine triggered a high antibody titer, with comparable specificity for morphine, 6-acetylmorphine, and heroin, but no interaction with dissimilar therapeutic opioid compounds, including buprenorphine, naloxone, and nalorphine, was observed. The vaccine significantly prevented the elevation of dopamine levels in the nucleus accumbens induced by a single morphine challenge. Moreover, the vaccine prevented the expression of morphine-induced locomotor sensitization and heroin-primed reinstatement of heroin seeking, suggesting its potential for preventing relapse.

CONCLUSION

These results demonstrate that active immunization with the present vaccine induces a robust morphine/heroin-specific antibody response in rats and attenuates the behavioral effects of morphine and heroin.

Mechanisms of the placebo response in pain in osteoarthritis

INTRODUCTION

Administration of a placebo associates with symptomatic improvement in many conditions--the so-called placebo response. In this review we explain the concept of placebo response, examine the data that supports existence in osteoarthritis (OA), and discuss its possible mechanisms and determinants.

METHODS

A Pubmed literature search was carried out. Key articles were identified, and their findings discussed in a narrative review.

RESULTS

Pain, stiffness, self-reported function and physician-global assessment in OA clearly improve in response to placebo. However, more objective measures such as quadriceps strength and radiographic progression appear less responsive. Although not directly studied in OA, contextual effects, patient expectation and conditioning are believed to be the main mechanisms. Neurotransmitter changes that mediate placebo-induced analgesia include increased endogenous opioid levels, increased dopamine levels, and reduced levels of cholecystokinin. Almost all parts of the brain involved in pain processing are influenced during placebo-induced analgesia. Determinants of the magnitude of placebo response include the patient-practitioner interaction, treatment response expectancy, knowledge of being treated, patient personality traits and placebo specific factors such as the route and frequency of administration, branding, and treatment costs.

CONCLUSION

Clearer understanding of the neurobiology of placebo response validates its existence as a real phenomenon. Although routine administration of placebo for symptomatic improvement is difficult to justify, contextual factors that enhance treatment response should be employed in the management of chronic painful conditions such as OA where available treatments have only modest efficacy.

Placebo response to manual therapy: something out of nothing?

The mechanisms through which manual therapy inhibits musculoskeletal pain are likely multifaceted and related to the interaction between the intervention, the patient, the practitioner, and the environment. Placebo is traditionally considered an inert intervention; however, the pain research literature suggests that placebo is an active hypoalgesic agent. Placebo response likely plays a role in all interventions for pain and we suggest that the same is true for the treatment effects associated with manual therapy. The magnitude of a placebo response may be influenced by negative mood, expectation, and conditioning. We suggest that manual therapists conceptualize placebo not only as a comparative intervention, but also as a potential active mechanism to partially account for treatment effects associated with manual therapy. We are not suggesting manual therapists include known sham or ineffective interventions in their clinical practice, but take steps to maximize placebo responses to reduce pain.

Guided imagery for non-musculoskeletal pain: a systematic review of randomized clinical trials

CONTEXT

Our previous review of the literature concluded that there is encouraging evidence that guided imagery alleviates musculoskeletal pain, but the value of guided imagery in the management of non-musculoskeletal pain remains uncertain.

OBJECTIVES

The objective of this systematic review was to assess the effectiveness of guided imagery as a treatment option for non-musculoskeletal pain.

METHODS

Six databases were searched from their inception to February 2011. Randomized clinical trials were considered if they investigated guided imagery in human patients with any type of non-musculoskeletal pain in any anatomical location and assessed pain as a primary outcome measure. Trials of motor imagery and hypnosis were excluded. The selection of studies, data extraction, and validation were performed independently by two reviewers.

RESULTS

Fifteen randomized clinical trials met the inclusion criteria. Their methodological quality was generally poor. Eleven trials found that guided imagery led to a significant reduction of non-musculoskeletal pain. Four studies found no change in non-musculoskeletal pain with guided imagery in comparison with progressive relaxation, standard care, or no treatment.

CONCLUSION

The evidence that guided imagery alleviates non-musculoskeletal pain is encouraging but remains inconclusive.

Placebo analgesia: cognitive influences on therapeutic outcome

The therapeutic response to a drug treatment is a mixture of direct pharmacological action and placebo effect. Therefore, harnessing the positive aspects of the placebo effect and reducing the negative ones could potentially benefit the patient. This article is aimed at providing an overview for clinicians of the importance of contextual psychosocial variables in determining treatment response, and the specific focus is on determinants of the placebo response. A better understanding of the physiological, psychological, and social mechanisms of placebo may aid in predicting which contexts have the greatest potential for inducing positive treatment responses. We examine the evidence for the role of psychological traits, including optimism, pessimism, and the effect of patient expectations on therapeutic outcome. We discuss the importance of the patient-practitioner relationship and how this can be used to enhance the placebo effect, and we consider the ethical challenges of using placebos in clinical practice.

Nicotinamide, NAD(P)(H), and Methyl-Group Homeostasis Evolved and Became a Determinant of Ageing Diseases: Hypotheses and Lessons from Pellagra

Compartmentalized redox faults are common to ageing diseases. Dietary constituents are catabolized to NAD(H) donating electrons producing proton-based bioenergy in coevolved, cross-species and cross-organ networks. Nicotinamide and NAD deficiency from poor diet or high expenditure causes pellagra, an ageing and dementing disorder with lost robustness to infection and stress. Nicotinamide and stress induce Nicotinamide-N-methyltransferase (NNMT) improving choline retention but consume methyl groups. High NNMT activity is linked to Parkinson's, cancers, and diseases of affluence. Optimising nicotinamide and choline/methyl group availability is important for brain development and increased during our evolution raising metabolic and methylome ceilings through dietary/metabolic symbiotic means but strict energy constraints remain and life-history tradeoffs are the rule. An optimal energy, NAD and methyl group supply, avoiding hypo and hyper-vitaminoses nicotinamide and choline, is important to healthy ageing and avoids utilising double-edged symbionts or uncontrolled autophagy or reversions to fermentation reactions in inflammatory and cancerous tissue that all redistribute NAD(P)(H), but incur high allostatic costs.

Sex and gender in adverse drug events, addiction, and placebo

Sex-gender-based differences in response to pharmaceutical treatments are still under evaluation but evidence already exists regarding the impact of sex-gender-related differences on drug safety profile, drug abuse/addiction, and placebo effects. For a number of drugs it is well recognized that a sex-gender dimorphic profile in terms of drug adverse effects exists and appears to be more frequent and severe in women than in men. However, it is not well known whether this is due to pharmacodynamic or pharmacokinetic differences. Indeed the optimization of therapy requires that attention is paid to single sex-gender. Numerous pharmacokinetic, pharmacodynamic, and sociocultural differences between women and men in drug abuse have been described. Here we focus on sex-gender differences in alcoholism and nicotine addiction. The relevance of sex and gender differences in addiction appear to be relevant. Specific programs aimed to address addicted women's specific needs (child care, pregnancy, housing, and violence and others) are recommended. Finally, this article discusses the possible effect of sex-gender on placebo response in the light of the more significant recent literature evidencing that studies are urgently required in order to better understand the role of sex-gender on placebo mechanism and its impact on randomized clinical trials outcomes.

Placebo expectations and the detection of somatic information

In a laboratory study we examined the hypothesis that placebo expectations enhance the initial identification of placebo-relevant sensations over placebo-irrelevant sensations. Participants (N = 102) were randomly assigned to one of three expectation groups. In the first group, participants ingested a placebo capsule and were told it was caffeine (deceptive expectation). In a second group, participants ingested a placebo capsule and were told it may be caffeine or it may be a placebo (double-blind expectation). Participants in the third group were given no expectation. All participants then tallied the placebo-relevant and placebo-irrelevant sensations they experienced during a 7-min period. Participants in the deceptive expectation group identified more placebo-relevant sensations than placebo-irrelevant sensations. No-expectation participants identified more placebo-irrelevant sensations than placebo-relevant sensations. Participants given the double-blind expectation identified an equal amount of placebo-relevant and irrelevant sensations. The amount of both placebo-relevant and placebo-irrelevant sensations detected mediated the relationship between the expectation manipulation and subsequent symptom reports. These data support the position that expectations cause placebo responding, in part, by altering how one identifies bodily sensations.

Placebo effect studies are susceptible to response bias and to other types of biases

OBJECTIVE

Investigations of the effect of placebo are often challenging to conduct and interpret. The history of placebo shows that assessment of its clinical significance has a real potential to be biased. We analyze and discuss typical types of bias in studies on placebo.

STUDY DESIGN AND SETTING

A methodological analysis and discussion.

RESULTS

The inherent nonblinded comparison between placebo and no-treatment is the best research design we have in estimating effects of placebo, both in a clinical and in an experimental setting, but the difference between placebo and no-treatment remains an approximate and fairly crude reflection of the true effect of placebo interventions. A main problem is response bias in trials with outcomes that are based on patients' reports. Other biases involve differential co-intervention and patient dropouts, publication bias, and outcome reporting bias. Furthermore, extrapolation of results to a clinical settings are challenging because of a lack of clear identification of the causal factors in many clinical trials, and the nonclinical setting and short duration of most laboratory experiments.

CONCLUSIONS

Creative experimental efforts are needed to assess rigorously the clinical significance of placebo interventions and investigate the component elements that may contribute to the therapeutic benefit.

Dispositional optimism predicts placebo analgesia

Based on prior research identifying dispositional optimism as a predictor of placebo responding, the present study tested the hypothesis that individuals high in optimism would be more likely to respond to a placebo analgesic. Optimists and pessimists were randomly assigned to a placebo expectation condition or a no expectation condition before a cold pressor task. Blood pressure and heart rate were recorded before and during the cold pressor task, and participant ratings of pain and expectations were obtained immediately after the task. Analysis of the expectation manipulation revealed that the placebo instruction was successful in altering participant expectancy during the cold pressor. Supporting the main hypothesis, dispositional optimism was associated with lower pain ratings in the placebo condition but not in the control condition. Because dispositional optimism can alter placebo responding to laboratory pain, future studies should examine the potential role that this individual difference factor may play in patient responsivity to pharmacological and nonpharmacological treatments for clinical pain.

PERSPECTIVE

This study examined the possibility that individual differences can predict placebo analgesia. Participants were randomly assigned to receive either a placebo expectation or no expectation before a cold pressor task. Dispositional optimism was related to less cold pressor pain in the placebo condition as compared with the control condition.

The silent healer: the role of communication in placebo effects

Placebo effects have an ambiguous reputation, as they are associated with sham treatment and deceit on the one hand and as interesting phenomena, which might be clinically relevant on the other. The goal of this paper is to demonstrate that placebo effects are relevant and can be used as an effective part of many treatments by using communication targeting placebo effect mechanisms. We examined the history of placebos and the placebo effect, addressing common misconceptions and disentangling ambiguities. We then reviewed whether the placebo effect can be robustly shown in the current literature, and zoomed in on the plausible mechanisms (conditioning, expectancies and affect manipulation) through which the placebo effect might be produced. Observing the link with the doctor-patient communication literature, and pleading for a better integration of the two research traditions we conclude by setting out a research agenda for testing the role of communication in placebo effects.

The placebo effect and homeopathy

BACKGROUND

Like other forms of medicine, including Complementary and Alternative Medicine (CAM), homeopathy elicits expectations in patients. The physician-patient relationship, personal and comprehensive treatment and lack of adverse effects are elements in creating positive expectations. Other elements may be associated with negative expectations.

METHODS

We conducted a systematic literature review on placebo and nocebo effects in acupuncture and homeopathy using Medline.

RESULTS

Findings on the psychophysiological and neuromediating mechanisms of the placebo-nocebo phenomenon are reviewed. Studies of these effects reveal how expectations and unconscious conditioning can be measured by imaging and EEG methods. They result in significant, non-specific therapeutic effects, which may confuse the evaluation of the specific therapeutic effects treatment, hampering selection of the simillimum.

CONCLUSIONS

Directions for future research on non-specific therapeutic effects of homeopathy to improve clinical practice and clinical research are discussed.

Placebo interventions for all clinical conditions

BACKGROUND

Placebo interventions are often claimed to substantially improve patient-reported and observer-reported outcomes in many clinical conditions, but most reports on effects of placebos are based on studies that have not randomised patients to placebo or no treatment. Two previous versions of this review from 2001 and 2004 found that placebo interventions in general did not have clinically important effects, but that there were possible beneficial effects on patient-reported outcomes, especially pain. Since then several relevant trials have been published.

OBJECTIVES

Our primary aims were to assess the effect of placebo interventions in general across all clinical conditions, and to investigate the effects of placebo interventions on specific clinical conditions. Our secondary aims were to assess whether the effect of placebo treatments differed for patient-reported and observer-reported outcomes, and to explore other reasons for variations in effect.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library Issue 4, 2007), MEDLINE (1966 to March 2008), EMBASE (1980 to March 2008), PsycINFO (1887 to March 2008) and Biological Abstracts (1986 to March 2008). We contacted experts on placebo research, and read references in the included trials.

SELECTION CRITERIA

We included randomised placebo trials with a no-treatment control group investigating any health problem.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data. We contacted study authors for additional information. Trials with binary data were summarised using relative risk (a value of less than 1 indicates a beneficial effect of placebo), and trials with continuous outcomes were summarised using standardised mean difference (a negative value indicates a beneficial effect of placebo).

MAIN RESULTS

Outcome data were available in 202 out of 234 included trials, investigating 60 clinical conditions. We regarded the risk of bias as low in only 16 trials (8%), five of which had binary outcomes.In 44 studies with binary outcomes (6041 patients), there was moderate heterogeneity (P < 0.001; I(2) 45%) but no clear difference in effects between small and large trials (symmetrical funnel plot). The overall pooled effect of placebo was a relative risk of 0.93 (95% confidence interval (CI) 0.88 to 0.99). The pooled relative risk for patient-reported outcomes was 0.93 (95% CI 0.86 to 1.00) and for observer-reported outcomes 0.93 (95% CI 0.85 to 1.02). We found no statistically significant effect of placebo interventions in four clinical conditions that had been investigated in three trials or more: pain, nausea, smoking, and depression, but confidence intervals were wide. The effect on pain varied considerably, even among trials with low risk of bias.In 158 trials with continuous outcomes (10,525 patients), there was moderate heterogeneity (P < 0.001; I(2) 42%), and considerable variation in effects between small and large trials (asymmetrical funnel plot). It is therefore a questionable procedure to pool all the trials, and we did so mainly as a basis for exploring causes for heterogeneity. We found an overall effect of placebo treatments, standardised mean difference (SMD) -0.23 (95% CI -0.28 to -0.17). The SMD for patient-reported outcomes was -0.26 (95% CI -0.32 to -0.19), and for observer-reported outcomes, SMD -0.13 (95% CI -0.24 to -0.02). We found an effect on pain, SMD -0.28 (95% CI -0.36 to -0.19)); nausea, SMD -0.25 (-0.46 to -0.04)), asthma (-0.35 (-0.70 to -0.01)), and phobia (SMD -0.63 (95% CI -1.17 to -0.08)). The effect on pain was very variable, also among trials with low risk of bias. Four similarly-designed acupuncture trials conducted by an overlapping group of authors reported large effects (SMD -0.68 (-0.85 to -0.50)) whereas three other pain trials reported low or no effect (SMD -0.13 (-0.28 to 0.03)). The pooled effect on nausea was small, but consistent. The effects on phobia and asthma were very uncertain due to high risk of bias. There was no statistically significant effect of placebo interventions in the seven other clinical conditions investigated in three trials or more: smoking, dementia, depression, obesity, hypertension, insomnia and anxiety, but confidence intervals were wide.Meta-regression analyses showed that larger effects of placebo interventions were associated with physical placebo interventions (e.g. sham acupuncture), patient-involved outcomes (patient-reported outcomes and observer-reported outcomes involving patient cooperation), small trials, and trials with the explicit purpose of studying placebo. Larger effects of placebo were also found in trials that did not inform patients about the possible placebo intervention.

AUTHORS' CONCLUSIONS

We did not find that placebo interventions have important clinical effects in general. However, in certain settings placebo interventions can influence patient-reported outcomes, especially pain and nausea, though it is difficult to distinguish patient-reported effects of placebo from biased reporting. The effect on pain varied, even among trials with low risk of bias, from negligible to clinically important. Variations in the effect of placebo were partly explained by variations in how trials were conducted and how patients were informed.

Differences in adverse effect reporting in placebo groups in SSRI and tricyclic antidepressant trials: a systematic review and meta-analysis

BACKGROUND

Biases in adverse effect reporting in randomized controlled trials (RCTs) [e.g. due to investigator expectations or assessment quality] can be quantified by studying the rates of adverse events reported in the placebo arms of such trials.

OBJECTIVE

We compared the rates of adverse effects reported in the placebo arms of tricyclic antidepressant (TCA) trials and placebo arms of selective serotonin reuptake inhibitor (SSRI) trials.

METHODS

We conducted a literature search for RCTs across PUBMED, Scopus and the Cochrane Central Register of Controlled Trials (CENTRAL). Only studies allowing adverse effect analysis were included. Publication year ranged from 1981 to 2007.

RESULTS

Our systematic review and meta-analysis included 143 placebocontrolled RCTs and data from 12,742 patients. Only 21% of studies used structured and systematic adverse effect ascertainment strategies. The way in which trials recorded adverse events influenced the rate of adverse effects substantially. Systematic assessment led to higher rates than less systematic assessment. Far more adverse effects were reported in TCA-placebo groups compared with SSRI-placebo groups, e.g. dry mouth (odds ratio [OR] = 3.5; 95% CI 2.9, 4.2); drowsiness (OR = 2.7; 95%CI 2.2, 3.4); constipation (OR= 2.7; 95%CI 2.1, 3.6); sexual problems (OR =2.3; 95%CI 1.5, 3.5). Regression analyses controlling for various influencing factors confirmed the results.

CONCLUSION

Adverse effect profiles reported in clinical trials are strongly influenced by expectations from investigators and patients. This difference cannot be attributed to ascertainment methods. Adverse effect patterns of the drug group are closely related to adverse effects of the placebo group. These results question the validity of the assumption that adverse effects in placebo groups reflect the 'drug-unspecific effects'.

The placebo effect: plugging the nostrils of unmet needs

Many common treatments for rhinitis symptoms are inadequate or ineffective. This may be in part because the drug does not address the pathologically altered mechanism of the rhinopathy. Objective measures may not detect treatment effects, or the treatment end points may be only subjective in nature. In many cases, these issues have not arisen because of potent placebo effects. Understanding the psychological, pharmacologic, and physiologic components of placebos is important for separating true treatment effects from those of the excipients in the vehicle. Separating the wasteful and potentially harmful effects of those excipients from the harmless and often partially beneficial effects on temporary symptom control is an important issue in clinical pharmacology that can aid in effective clinical trial design, use of objective and subjective test measures, and development of drugs to treat rhinitis.

The mechanisms of manual therapy in the treatment of musculoskeletal pain: a comprehensive model

Prior studies suggest manual therapy (MT) as effective in the treatment of musculoskeletal pain; however, the mechanisms through which MT exerts its effects are not established. In this paper we present a comprehensive model to direct future studies in MT. This model provides visualization of potential individual mechanisms of MT that the current literature suggests as pertinent and provides a framework for the consideration of the potential interaction between these individual mechanisms. Specifically, this model suggests that a mechanical force from MT initiates a cascade of neurophysiological responses from the peripheral and central nervous system which are then responsible for the clinical outcomes. This model provides clear direction so that future studies may provide appropriate methodology to account for multiple potential pertinent mechanisms.

Pain relief for the removal of femoral sheath in interventional cardiology adult patients

BACKGROUND

There is considerable variation in use of pain relief for managing pain or discomfort of femoral sheath removal. Efficacy of pain relief to promote comfort during this procedure or to reduce the incidence of vascular and procedural complications has not been established.

OBJECTIVES

Assess efficacy of pain relief used to manage pain of femoral sheath removal in adults after interventional cardiology.Determine if pain relief influences rate of complications associated with this procedure.

SEARCH STRATEGY

Databases searched in August 2007: Cochrane Pain, Palliative and Supportive Care Group Trials Register, Cochrane Heart Group Trials Register, Cochrane CENTRAL, MEDLINE, EMBASE, CINAHL, PubMed, Australia's Australasian Medical Index, National Research Centre, Web of Knowledge and Digital Dissertations.

SELECTION CRITERIA

Randomised studies comparing opioid, local anaesthetic, anxiolytic, no treatment or placebo administered for alleviation of pain or discomfort of the femoral sheath removal procedure, were sought.

DATA COLLECTION AND ANALYSIS

Two review authors assessed trial quality and extracted data. Weighted mean differences (WMD) were calculated where meta-analysis of pain score data was feasible. Adverse effects information was collected.

MAIN RESULTS

Four trials involving 971 participants were included. All results were reported using a zero to ten pain scale. Three trials (four treatment arms) involving 498 participants compared subcutaneous lignocaine with control; with no significant difference between pain scores; WMD 0.12 (95% CI -0.46 to 0.69). Two trials (three treatment arms) involving 399 participants compared intravenous pain regimens with control. A significant reduction in pain score with an intravenous pain regimen (opioid and anxiolytic) was observed when compared with placebo; WMD -0.90 (95% CI -1.54 to -0.27). One study involving 60 participants compared levobupivacaine with placebo. Longer-acting local anaesthetic significantly lowered pain score by -1.10 (95% CI -1.26 to -0.94). Data is insufficient to identify any influence of pain regimens on incidence of vascular and procedural complications. No trials reported appropriate blinding for treatment arms. The largest trial, comprising 661 participants was unblinded with a quality score of two out of five.

AUTHORS' CONCLUSIONS

Intravenous pain regimens and levobupivacaine may have greater efficacy when compared to control for the management of pain related to femoral sheath removal. However, a definitive study is still required because the clinical difference is small. There is no evidence to support the use of subcutaneous lignocaine for the relief of femoral sheath removal related pain. There is insufficient evidence to determine if pain relief influences the rate of complications.

[Clinical significance of the placebo effect]

Placebo controlled studies examining clinical problems, e.g. in pain therapy, are considered the "gold standard" for evidence-based medicine. In these studies the placebo effect itself is not the main focus of interest, but serves more as a control for the specificity of the effect of a certain treatment. What physicians in this context often do not realize is that the placebo effect itself represents a true measurable correlate of an organism's psycho-neurobiological response and, thereby, influences the healing process, e.g. the pain relief. Placebo is, therefore, not equivalent to "no treatment". The number of placebo responders, the degree and the duration of the placebo effect is not fixed, but are subject to a much greater variability then hitherto believed. The myth that placebo responders have a certain personality has not been proven correct; instead, the relationships between physicians and patients as well as sociocultural factors have a considerable impact on the placebo effect. Psychological theories explain that classical conditioning, enhanced expectation and motivation of the patient determine the degree of the placebo effect. These directly influence neurobiological systems such as the endogenous opioids which according to modern brain imaging are predominantly activated in pain-relevant areas and contribute to the effect of placebo analgesia. Placebo effects that should be deliberately excluded in controlled clinical trials, can be desirable in clinical practice to optimize the total therapeutic effect. This should mean that the context effect of each therapeutic intervention is maximized towards an improved therapeutic effect, as outlined in the recent AWMF guidelines for postoperative pain therapy, but should not include the administration of an inert substance. The latter is controlled by rigorous ethical guidelines and is only permitted in the context of ethically approved controlled clinical trials. A possible alternative is suggested by Benedetti et al. in which the hidden administration of an active substance identifies the specific response in contrast to the open application of the same substance characterizing the specific plus the placebo effect, after which the pure placebo effect can be determined.