Cannabinoids, cannabis, and cannabis-based medicines for pain management: an overview of systematic reviews

Effectiveness of pharmacological therapies for fibromyalgia syndrome in adults: an overview of Cochrane Reviews

OBJECTIVES

To summarize and evaluate Cochrane reviews of pharmacological therapies for adults with fibromyalgia syndrome (FMS) pain.

METHODS

Systematic search of Cochrane Database of Systematic Reviews to May 2024. Generic quality assessment used AMSTAR-2 criteria, validity checks of potentially critical factors in evaluation of analgesic efficacy and assessment of susceptibility of results to publication bias. Pain outcomes were participant-reported pain relief of ≥30% or ≥50%, or PGIC much or very much improved.

RESULTS

Twenty-one reviews (87 trials, 17 631 patients) were included. All rated moderate (15) or high-quality (6) using AMSTAR-2 and at least seven of eight critical pain criteria were met by 13 of 21 reviews. Diagnosis of FMS used recognized criteria. Seven reviews found no trials (carbamazepine, clonazepam, lamotrigine, phenytoin, oxycodone, topiramate or valproate), seven had limited and inadequate data (antipsychotics, cannabinoids, combination therapy, gabapentin, lacosamide, monoamine oxidase inhibitors, NSAIDs) and two were subject to publication bias (amitriptyline, SSRI). Mirtazapine had moderate evidence of no effect. Duloxetine, milnacipran and pregabalin had moderate/good evidence of substantial pain relief for 4-12 weeks in around 1 in 10 adults with moderate or severe FMS pain, without evidence of efficacy beyond six months. Serious adverse events were no more common than with placebo. There was no evidence about who might benefit or experience adverse events. There was no substantial efficacy evidence for other medicines.

CONCLUSIONS

Duloxetine, milnacipran and pregabalin had good evidence that about 1 person in 10 with moderate or severe pain experienced pain intensity reduction by at least 50%.

Pharmacotherapy and non-invasive neuromodulation for neuropathic pain: a systematic review and meta-analysis

BACKGROUND

There remains a substantial unmet need for effective and safe treatments for neuropathic pain. The Neuropathic Pain Special Interest Group aimed to update treatment recommendations, published in 2015, on the basis of new evidence from randomised controlled trials, emerging neuromodulation techniques, and advances in evidence synthesis.

METHODS

For this systematic review and meta-analysis, we searched Embase, PubMed, the International Clinical Trials Registry, and ClinicalTrials.gov from data inception for neuromodulation trials and from Jan 1, 2013, for pharmacological interventions until Feb 12, 2024. We included double-blind, randomised, placebo-controlled trials that evaluated pharmacological and neuromodulation treatments administered for at least 3 weeks, or if there was at least 3 weeks of follow-up, and which included at least ten participants per group. Trials included participants of any age with neuropathic pain, defined by the International Association for the Study of Pain. We excluded trials with enriched enrolment randomised withdrawal designs and those with participants with mixed aetiologies (ie, neuropathic and non-neuropathic pain) and conditions such as complex regional pain syndrome, low back pain without radicular pain, fibromyalgia, and idiopathic orofacial pain. We extracted summary data in duplicate from published reports, with discrepancies reconciled by a third independent reviewer on the platform Covidence. The primary efficacy outcome was the proportion of responders (50% or 30% reduction in baseline pain intensity or moderate pain relief). The primary safety outcome was the number of participants who withdrew from the treatment owing to adverse events. We calculated a risk difference for each comparison and did a random-effects meta-analysis. Risk differences were used to calculate the number needed to treat (NNT) and the number needed to harm (NNH) for each treatment. Risk of bias was assessed by use of the Cochrane risk of bias tool 2 and certainty of evidence assessed by use of GRADE. Recommendations were based on evidence of efficacy, adverse events, accessibility, and cost, and feedback from engaged lived experience partners. This study is registered on PROSPERO, CRD42023389375.

FINDINGS

We identified 313 trials (284 pharmacological and 29 neuromodulation studies) for inclusion in the meta-analysis. Across all studies, 48 789 adult participants were randomly assigned to trial groups (20 611 female and 25 078 male participants, where sex was reported). Estimates for the primary efficacy and safety outcomes were tricyclic antidepressants (TCAs) NNT=4·6 (95% CI 3·2-7·7), NNH=17·1 (11·4-33·6; moderate certainty of evidence), α2δ-ligands NNT=8·9 (7·4-11·10), NNH=26·2 (20·4-36·5; moderate certainty of evidence), serotonin and norepinephrine reuptake inhibitors (SNRIs) NNT=7·4 (5·6-10·9), NNH=13·9 (10·9-19·0; moderate certainty of evidence), botulinum toxin (BTX-A) NNT=2·7 (1·8-9·61), NNH=216·3 (23·5-∞; moderate certainty of evidence), capsaicin 8% patches NNT=13·2 (7·6-50·8), NNH=1129·3 (135·7-∞; moderate certainty of evidence), opioids NNT=5·9 (4·1-10·7), NNH=15·4 (10·8-24·0; low certainty of evidence), repetitive transcranial magnetic stimulation (rTMS) NNT=4·2 (2·3-28·3), NNH=651·6 (34·7-∞; low certainty of evidence), capsaicin cream NNT=6·1 (3·1-∞), NNH=18·6 (10·6-77·1; very low certainty of evidence), lidocaine 5% plasters NNT=14·5 (7·8-108·2), NNH=178·0 (23·9-∞; very low certainty of evidence). The findings provided the basis for a strong recommendation for use of TCAs, α2δ-ligands, and SNRIs as first-line treatments; a weak recommendation for capsaicin 8% patches, capsaicin cream, and lidocaine 5% plasters as second-line recommendation; and a weak recommendation for BTX-A, rTMS, and opioids as third-line treatments for neuropathic pain.

INTERPRETATION

Our results support a revision of the Neuropathic Pain Special Interest Group recommendations for the treatment of neuropathic pain. Treatment outcomes are modest and for some treatments uncertainty remains. Further large placebo-controlled or sham-controlled trials done over clinically relevant timeframes are needed.

FUNDING

NeuPSIG and ERA-NET Neuron.

UK Medical Cannabis Registry: An Analysis of Outcomes of Medical Cannabis Therapy for Hypermobility-Associated Chronic Pain

OBJECTIVE

The study aims to evaluate the clinical outcomes in patients with hypermobility spectrum disorder (HSD) and hypermobile Ehlers-Danlos syndrome (hEDS) with chronic pain following treatment with cannabis-based medicinal products (CBMPs).

METHODS

This was a case series conducted with the UK Medical Cannabis Registry. The primary outcomes were changes in the following validated patient-reported outcome measures at 1, 3, 6, 12, and 18 months compared with baseline: Short-Form McGill Pain Questionnaire 2 (SF-MPQ-2), pain visual analog scale score (Pain-VAS), Brief Pain Inventory (BPI), five-level EQ-5D (EQ-5D-5L), Single-Item Sleep Quality Scale (SQS), General Anxiety Disorder Seven-Item Scale (GAD-7), and Patient Global Impression of Change. The incidence of adverse events was analyzed as secondary outcomes. Statistical significance was defined as P <0.050.

RESULTS

A total of 161 patients met inclusion criteria. Improvements were observed in BPI severity and interference subscales, SF-MPQ-2, and Pain-VAS (P < 0.001). Changes were also seen in the EQ-5D-5L index value, SQS, and GAD-7 (P < 0.001). A total of 50 patients (31.06%) reported one or more adverse event with a total incidence of 601 (373.29%). The most frequent rating for adverse events was moderate (n = 258; 160.25%), with headache being the most common (n = 44; 27.33%).

CONCLUSION

An association was identified between patients with HSD/hEDS with chronic pain and improvements in pain-specific and general health-related quality of life following the commencement of CBMPs. CBMPs were also well tolerated at 18 months. These findings must be interpreted within the context of the limitations of study design but add further weight to calls for randomized controlled trials.

ENTRUST-PE Network, O'Connell NE, Belton J, Crombez G, Eccleston C, Fisher E, Ferraro MC, Hood A, Keefe F, Knaggs R, Norris E, Palermo TM, Pickering G, Pogatzki-Zahn E, Rice AS, Richards G, Segelcke D, Smart KM, Soliman N, Stewart G, Tölle T, Turk D, Vollert J, Wainwright E, Wilkinson J, Williams ACDC. Enhancing the trustworthiness of pain research: A call to action

The personal, social and economic burden of chronic pain is enormous. Tremendous research efforts are being directed toward understanding, preventing, and managing chronic pain. Yet patients with chronic pain, clinicians and the public are sometimes poorly served by an evidence architecture that contains multiple structural weaknesses. These include incomplete research governance, a lack of diversity and inclusivity, inadequate stakeholder engagement, poor methodological rigour and incomplete reporting, a lack of data accessibility and transparency, and a failure to communicate findings with appropriate balance. These issues span pre-clinical research, clinical trials and systematic reviews and impact the development of clinical guidance and practice. Research misconduct and inauthentic data present a further critical risk. Combined, they increase uncertainty in this highly challenging area of study and practice, drive the provision of low value care, increase costs and impede the discovery of more effective solutions. In this focus article, we explore how we can increase trust in pain science, by examining critical challenges using contemporary examples, and describe a novel integrated conceptual framework for enhancing the trustworthiness of pain science. We end with a call for collective action to address this critical issue. PERSPECTIVE: Multiple challenges can adversely impact the trustworthiness of pain research and health research more broadly. We present ENTRUST-PE, a novel, integrated framework for more trustworthy pain research with recommendations for all stakeholders in the research ecosystem, and make a call to action to the pain research community.

Clinical and Public Health Challenge of Handling Synthetic Cathinone and Cannabinoid Abuse in Pediatric Care: A Narrative Review

BACKGROUND

Synthetic cathinones and cannabinoids have emerged as significant public health concerns, particularly in pediatric populations. Marketed under deceptive names such as "bath salts" and "K2/Spice", these substances pose unique challenges due to their accessibility, potency, and unpredictable effects. This narrative review synthesizes evidence on the toxicological effects of synthetic cathinones and cannabinoids in pediatric patients, emphasizing clinical presentations, management challenges, and public health implications.

METHODS

A structured narrative review was conducted using PubMed and Scopus databases to identify peer-reviewed studies published between January 2010 and September 2024. The selected articles focus on neuropsychiatric, systemic, and management outcomes associated with these substances in individuals aged 0-18 years.

RESULTS

Five studies demonstrate that synthetic cathinones frequently cause seizures, sympathomimetic toxidrome (tachycardia, hypertension), and neuropsychiatric effects like paranoia and catatonia. Seven studies show synthetic cannabinoids induce psychosis, respiratory depression requiring ventilation in 12% of cases, and cardiovascular complications like myocardial ischemia. One study highlighted severe outcomes in pediatric accidental exposures, emphasizing the unpredictable and life-threatening effects of these substances, often exacerbated by co-ingestion with alcohol or THC.

CONCLUSIONS

Pediatric exposure to synthetic cathinones and cannabinoids results in severe and unpredictable toxicological effects, necessitating tailored clinical management strategies and enhanced diagnostic capabilities. Public health measures, including stringent regulatory controls, targeted education initiatives, and robust surveillance systems, are critical to mitigating these risks. A multidisciplinary approach is essential to safeguard vulnerable pediatric populations from the escalating dangers posed by synthetic drugs, and future research must address the long-term impacts and mechanisms of toxicity.

An early economic analysis of medical cannabis for the treatment of chronic pain

BACKGROUND

Cannabis-based medicinal products (CBMPs) are increasingly demonstrating effectiveness in treating a wide range of conditions, with a relatively high safety profile in clinical usage compared to other prescription pain medications and few contraindications. Consultation and other prescription-related costs are, at present, higher for CBMPs than for some other treatment options, leading to some concern around wider prescribing.

RESEARCH DESIGN AND METHODS

An early cost-effectiveness model was developed to estimate the impact of prescribing CBMPs alone and/or in addition to analgesics, physiotherapy, and cognitive behavioral therapy for chronic pain in the UK for 1 year.

RESULTS

Due to their comparative effectiveness, CBMPs were found to be cost saving. Various scenarios were model tested; in all scenarios where CBMPs decrease pain-level states, less resource use is required. Increased efficacy of 5% was conservatively assumed based on current Real-World Evidence. In this scenario, CBMPs were significantly more cost-effective, and as costs relating to the prescribing of these continue to fall, relative savings are predicted to increase.

CONCLUSION

These findings highlight the substantial cost saving that CBMPs may represent for the treatment of chronic pain patients, and the benefits for healthcare providers as a treatment for this often hard-to-treat population.

Narrative bias ("spin") is common in randomised trials and systematic reviews of cannabinoids for pain

ABSTRACT

We define narrative bias as a tendency to interpret information as part of a larger story or pattern, regardless of whether the facts support the full narrative. Narrative bias in title and abstract means that results reported in the title and abstract of an article are done so in a way that could distort their interpretation and mislead readers who had not read the whole article. Narrative bias is often referred to as "spin." It is prevalent in abstracts of scientific papers and is impactful because abstracts are often the only part of an article read. We found no extant narrative bias instrument suitable for exploring both efficacy and safety statements in randomized trials and systematic reviews of pain. We constructed a 6-point instrument with clear instructions and tested it on randomised trials and systematic reviews of cannabinoids and cannabis-based medicines for pain, with updated searches to April 2021. The instrument detected moderate or severe narrative bias in the title and abstract of 24% (8 of 34) of randomised controlled trials and 17% (11 of 64) of systematic reviews; narrative bias for efficacy and safety occurred equally. There was no significant or meaningful association between narrative bias and study characteristics in correlation or cluster analyses. Bias was always in favour of the experimental cannabinoid or cannabis-based medicine. Put simply, reading title and abstract only could give an incorrect impression of efficacy or safety in about 1 in 5 papers reporting on these products.

Cannabis medicine for chronic pain

In the last decade, patients with chronic pain have expressed increasing interest in cannabis-derived products for adjuvant therapy when treatment is deemed refractory to conventional analgesics. At present, clinical evidence to support this treatment approach appears to be sparse. Not because clinical studies as such are lacking, but rather as a result of methodological bias in relation to study design, patient populations, and treatment protocols. In this review, research in cannabis medicine for relief of chronic pain is reviewed, mainly with reference to published meta-analytic studies.

Cannabidiol (CBD) Products for Pain: Ineffective, Expensive, and With Potential Harms

Cannabidiol (CBD) attracts considerable attention for promoting good health and treating various conditions, predominantly pain, often in breach of advertising rules. Examination of available CBD products in North America and Europe demonstrates that CBD content can vary from none to much more than advertised and that potentially harmful other chemicals are often included. Serious harm is associated with chemicals found in CBD products and reported in children, adults, and the elderly. A 2021 International Association for the Study of Pain task force examined the evidence for cannabinoids and pain but found no trials of CBD. Sixteen CBD randomized trials using pharmaceutical-supplied CBD or making preparations from such a source and with pain as an outcome have been published subsequently. The trials were conducted in 12 different pain states, using 3 oral, topical, and buccal/sublingual administration, with CBD doses between 6 and 1,600 mg, and durations of treatment between a single dose and 12 weeks. Fifteen of the 16 showed no benefit of CBD over placebo. Small clinical trials using verified CBD suggest the drug to be largely benign; while large-scale evidence of safety is lacking, there is growing evidence linking CBD to increased rates of serious adverse events and hepatotoxicity. In January 2023, the Food and Drug Administration (FDA) announced that a new regulatory pathway for CBD was needed. Consumers and health care providers should rely on evidence-based sources of information on CBD, not just advertisements. Current evidence is that CBD for pain is expensive, ineffective, and possibly harmful. PERSPECTIVE: There is no good reason for thinking that CBD relieves pain, but there are good reasons for doubting the contents of CBD products in terms of CBD content and purity.

Differences in prescribed medicinal cannabis use by cannabinoid product composition: Findings from the cannabis as medicine survey 2020 (CAMS-20) Australia-wide study

INTRODUCTION

Prescribed medicinal cannabis (MC) is an increasingly common prescription in Australia for treating pain, anxiety, and sleep disorders. Prescribed MC products generally contain tetrahydrocannabinol (THC) and/or cannabidiol (CBD) in a variety of dose levels and forms. It is unclear whether THC and CBD products are used by patients with different characteristics and for different conditions.

OBJECTIVES

To examine consumer experiences of using THC- and CBD-containing prescribed MC products to better understand how they are being used within the Australian context.

METHODS

We utilised data collected from an online anonymous cross-sectional survey of individuals (CAMS-20 survey), consisting of Australian residents using cannabis for therapeutic reasons. We focused on a subgroup of participants (N = 546) receiving prescribed MC products. We utilised linear, logistic, and multinomial regression modelling to analyse responses to survey questions based on the cannabinoid profile of the prescribed product.

RESULTS

Participants prescribed THC-dominant MC products were statistically more likely to be younger, male, and to prefer inhaled routes of administration than participants using CBD-dominant products who were older, female, and preferred oral routes of administration. Pain and mental health were the most common reasons for all types of prescribed MC, but were more likely to be treated with THC than CBD despite the significantly higher risk of mild to severe drowsiness, dry mouth and eye irritation. Consumer reported effectiveness of prescribed MC was very positive, particularly for THC-containing products. Consumers on opioids and antipsychotics were statistically more likely to be prescribed THC-containing products than products containing CBD only, despite the greater risk of impairment.

CONCLUSIONS

This Australia-wide study found clear differences in consumer-reported experiences of prescribed THC- and CBD-containing products. Current prescriptions of these products do not always align with relevant clinical guidance. Educating prescribers around cannabinoid products is essential to ensure optimal prescribing practices and to prevent avoidable drug side effects and interactions.

Pharmacokinetics and pharmacodynamics of cannabis-based medicine in a patient population included in a randomized, placebo-controlled, clinical trial

Information on the pharmacokinetics (PK) and pharmacodynamics (PD) of orally administered cannabis-based medicine (CBM) in capsule formulation in patient populations is sparse. In this exploratory study, we aimed to evaluate the PK and PD in a probable steady state of CBM in neuropathic pain and spasticity in a population of patients with multiple sclerosis (MS). Of 134 patients participating in a randomized, double-blinded, placebo-controlled, trial, 23 patients with MS (17 female) mean age 52 years (range 21-67) were enrolled in this substudy. They received oral capsules containing Δ9 -tetrahydrocannabinol (THC, n = 4), cannabidiol (CBD, n = 6), a combination (THC&CBD, n = 4), or placebo (n = 9). Maximum doses were 22.5 mg (THC) and 45 mg (CBD) a day divided into three administrations. PD parameters were evaluated for pain and spasticity. Blood samples were analyzed using an ultra-high-performance liquid chromatography-tandem mass spectrometer after protein precipitation and phospholipid removal. PK parameters were estimated using computerized modeling. The variation in daily dose and PK between individuals was considerable in a steady state, yet comparable with previous reports from healthy controls. Based on a simulation of the best model, the estimated PK parameters (mean) for THC (5 mg) were Cmax 1.21 ng/mL, Tmax 2.68 h, and half-life 2.75 h, and for CBD (10 mg) were Cmax 2.67 ng/mL, Tmax 0.10 h, and half-life 4.95 h, respectively. No effect was found on the PD parameters, but the placebo response was considerable. More immediate adverse events were registered in the active treatment groups compared with the placebo group.

Oral cannabidiol (CBD) as add-on to paracetamol for painful chronic osteoarthritis of the knee: a randomized, double-blind, placebo-controlled clinical trial

Background

Painful knee osteoarthritis (KOA) is common, pharmacological treatment, however, is often hampered by limited tolerability. Cannabidiol, which preclinically showed anti-inflammatory, analgesic activity, could supplement established analgesics, but robust clinical trials are lacking. The aim of our study was to investigate the effects of oral high-dose CBD administered over 8 weeks on pain, function and patient global assessment as an add-on to continued paracetamol in chronic symptomatic KOA.

Methods

Prospective, randomized, placebo-controlled, double-blind, parallel-group study. Single center, Outpatient Clinic, Department of Special Anaesthesia and Pain Therapy at Medical University of Vienna, Austria. Eligibility criteria included: age: 18-98 years; painful KOA; score ≥5 on the pain subscale of the Western Ontario and McMasters Universities Osteoarthritis (WOMAC) Index; KOA confirmed by imaging. Participants were on continued dosage of paracetamol 3 g/d and randomly assigned by web-based software 1:1 to oral cannabidiol 600 mg/d (n = 43) or placebo (n = 43). Study period: 8 weeks. Primary outcome: Change in WOMAC pain subscale scores (0 = no pain, 10 = worst possible pain) from baseline to week 8 of treatment. Trial Registration: ClinicalTrials.gov Identifier: NCT04607603. Trial is completed.

Findings

The trial was conducted from October 1, 2020 to March 29, 2022. 159 patients screened, 86 randomized. Among 86 participants (mean age, 62.8 [SD 20.3] years; 60 females [69.8%]), 58 (67.4%) completed the trial. Mean baseline WOMAC pain subscale was 6.0 ± 1.1. Analysis: Intention-to-treat principal. Mean reduction in WOMAC pain subscale was 2.5 (95% CI: 1.8-3.3) in the cannabidiol group and 2.4 (95% CI: 1.7-3.2) in the placebo group with no significant group difference (p = 0.80). Adverse events were significantly more frequent with cannabidiol (cannabidiol: 135 [56%]; placebo: 105 [44%]) (p = 0.008). Rise above baseline of liver aminotransferases and gamma-glutamyltransferase was significantly more common in the cannabidiol (n = 15) than the placebo group (n = 5) (p = 0.02).

Interpretation

In KOA patients, oral high-dose add-on cannabidiol had no additional analgesic effect compared to adding placebo to continued paracetamol. Our results do not support the use of cannabidiol as an analgesic supplement in KOA.

Funding

Trigal Pharma GmbH.

Chronic wound-related pain, wound healing and the therapeutic potential of cannabinoids and endocannabinoid system modulation

Chronic wounds represent a significant burden on the individual, and the healthcare system. Individuals with chronic wounds report pain to be the most challenging aspect of living with a chronic wound, with current therapeutic options deemed insufficient. The cutaneous endocannabinoid system is an important regulator of skin homeostasis, with evidence of system dysregulation in several cutaneous disorders. Herein, we describe the cutaneous endocannabinoid system, chronic wound-related pain, and comorbidities, and review preclinical and clinical evidence investigating endocannabinoid system modulation for wound-related pain and wound healing. Based on the current literature, there is some evidence to suggest efficacy of endocannabinoid system modulation for promotion of wound healing, attenuation of cutaneous disorder-related inflammation, and for the management of chronic wound-related pain. However, there is 1) a paucity of preclinical studies using validated models, specific for the study of chronic wound-related pain and 2) a lack of randomised control trials and strong clinical evidence relating to endocannabinoid system modulation for wound-related pain. In conclusion, while there is some limited evidence of benefit of endocannabinoid system modulation in wound healing and wound-related pain management, further research is required to better realise the potential of targeting the endocannabinoid system for these therapeutic applications.

Experiences and Perceptions of Medical Cannabis among People Living with Chronic Pain and Community Pharmacists: A Qualitative Study in Canada

Background

The use of cannabis to treat chronic pain is under debate despite high expectations from patients. Qualitative data obtained by exploring both patients' and health professionals' perspectives are scarce.

Aims

This study aimed to understand the experiences and perceptions of people living with chronic pain and community pharmacists regarding the role of cannabis in chronic pain treatment in the Canadian context where both medical and recreational cannabis are legal.

Methods

We conducted 12 online focus groups (July 2020-February 2021) with 26 patients and 19 community pharmacists using semistructured discussion guides. All discussions were audio recorded and transcribed verbatim were analyzed using a reflexive thematic approach.

Results

We developed three themes related to patients' perspectives and three themes related to pharmacists' perspectives. Patients' perspectives included (1) cannabis as an alternative to other pain medications, (2) a new treatment with potential health-related risks, and (3) a therapy rather than a recreational drug. Pharmacists' perspectives included (1) challenges in monitoring drug interactions with cannabis in the context of scarce research data, (2) informing and treating patients self-medicating with cannabis amid its growing popularity, and (3) financial costs and legal constraints for patients.

Conclusions

This study highlights patients' and pharmacists' urgent need for reliable information regarding the benefits and risks of cannabis. Training tailored to pharmacists' needs and evidence-based information for patients should be developed to support pharmacists' practice, improve patients' experiences, and promote safe cannabis use.

Analysis of pain research literature through keyword Co-occurrence networks

Pain is a significant public health problem as the number of individuals with a history of pain globally keeps growing. In response, many synergistic research areas have been coming together to address pain-related issues. This work reviews and analyzes a vast body of pain-related literature using the keyword co-occurrence network (KCN) methodology. In this method, a set of KCNs is constructed by treating keywords as nodes and the co-occurrence of keywords as links between the nodes. Since keywords represent the knowledge components of research articles, analysis of KCNs will reveal the knowledge structure and research trends in the literature. This study extracted and analyzed keywords from 264,560 pain-related research articles indexed in IEEE, PubMed, Engineering Village, and Web of Science published between 2002 and 2021. We observed rapid growth in pain literature in the last two decades: the number of articles has grown nearly threefold, and the number of keywords has grown by a factor of 7. We identified emerging and declining research trends in sensors/methods, biomedical, and treatment tracks. We also extracted the most frequently co-occurring keyword pairs and clusters to help researchers recognize the synergies among different pain-related topics.

Answering Big Questions in Pain Medicine

The future of pain medicine is marked by many questions. What can other nations around the world learn from the opioid crisis that is still affecting the United States? The American opioid experience was mischaracterized and wrongly described, and its causes were misdiagnosed from the outset, leading to its mismanagement and the abandonment of many chronic pain patients to their suffering. There are a few new drugs in the analgesic armamentarium. What new targets do we have in pain medicine? There are many breakthroughs, discoveries, and potential new targets that could add to our analgesic prescribing choices. These include sigma receptors, d-amino acid oxidase, endoplasmic reticulum stress receptors, histone deacetylase, and others. Neuromodulation had been used with varying degrees of success for years, but with a simplistic approach based on the gate theory of pain. Despite our familiarity with neuromodulation and spinal cord stimulators, neuromodulation research indicates that the activation of glial cells may activate the immune system and enhance analgesia. Neuromodulation studies have concentrated on how electricity affects neuronal activity rather than how electrical activity could reduce pain. There are still more frontiers in our battle against pain and some promising avenues for treatments. This narrative review will try to summarize what can be done from the perspective of recent technological and pharmacological developments.

Cannabis-based medicines and medical cannabis for adults with cancer pain

BACKGROUND

Pain is a common symptom in people with cancer; 30% to 50% of people with cancer will experience moderate-to-severe pain. This can have a major negative impact on their quality of life. Opioid (morphine-like) medications are commonly used to treat moderate or severe cancer pain, and are recommended for this purpose in the World Health Organization (WHO) pain treatment ladder. Pain is not sufficiently relieved by opioid medications in 10% to 15% of people with cancer. In people with insufficient relief of cancer pain, new analgesics are needed to effectively and safely supplement or replace opioids.

OBJECTIVES

To evaluate the benefits and harms of cannabis-based medicines, including medical cannabis, for treating pain and other symptoms in adults with cancer compared to placebo or any other established analgesic for cancer pain.

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest search date was 26 January 2023.

SELECTION CRITERIA

We selected double-blind randomised, controlled trials (RCT) of medical cannabis, plant-derived and synthetic cannabis-based medicines against placebo or any other active treatment for cancer pain in adults, with any treatment duration and at least 10 participants per treatment arm.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. The primary outcomes were 1. proportions of participants reporting no worse than mild pain; 2. Patient Global Impression of Change (PGIC) of much improved or very much improved and 3. withdrawals due to adverse events. Secondary outcomes were 4. number of participants who reported pain relief of 30% or greater and overall opioid use reduced or stable; 5. number of participants who reported pain relief of 30% or greater, or 50% or greater; 6. pain intensity; 7. sleep problems; 8. depression and anxiety; 9. daily maintenance and breakthrough opioid dosage; 10. dropouts due to lack of efficacy; 11. all central nervous system adverse events. We used GRADE to assess certainty of evidence for each outcome.

MAIN RESULTS

We identified 14 studies involving 1823 participants. No study assessed the proportions of participants reporting no worse than mild pain on treatment by 14 days after start of treatment. We found five RCTs assessing oromucosal nabiximols (tetrahydrocannabinol (THC) and cannabidiol (CBD)) or THC alone involving 1539 participants with moderate or severe pain despite opioid therapy. The double-blind periods of the RCTs ranged between two and five weeks. Four studies with a parallel design and 1333 participants were available for meta-analysis. There was moderate-certainty evidence that there was no clinically relevant benefit for proportions of PGIC much or very much improved (risk difference (RD) 0.06, 95% confidence interval (CI) 0.01 to 0.12; number needed to treat for an additional beneficial outcome (NNTB) 16, 95% CI 8 to 100). There was moderate-certainty evidence for no clinically relevant difference in the proportion of withdrawals due to adverse events (RD 0.04, 95% CI 0 to 0.08; number needed to treat for an additional harmful outcome (NNTH) 25, 95% CI 16 to endless). There was moderate-certainty evidence for no difference between nabiximols or THC and placebo in the frequency of serious adverse events (RD 0.02, 95% CI -0.03 to 0.07). There was moderate-certainty evidence that nabiximols and THC used as add-on treatment for opioid-refractory cancer pain did not differ from placebo in reducing mean pain intensity (standardised mean difference (SMD) -0.19, 95% CI -0.40 to 0.02). There was low-certainty evidence that a synthetic THC analogue (nabilone) delivered over eight weeks was not superior to placebo in reducing pain associated with chemotherapy or radiochemotherapy in people with head and neck cancer and non-small cell lung cancer (2 studies, 89 participants, qualitative analysis). Analyses of tolerability and safety were not possible for these studies. There was low-certainty evidence that synthetic THC analogues were superior to placebo (SMD -0.98, 95% CI -1.36 to -0.60), but not superior to low-dose codeine (SMD 0.03, 95% CI -0.25 to 0.32; 5 single-dose trials; 126 participants) in reducing moderate-to-severe cancer pain after cessation of previous analgesic treatment for three to four and a half hours (2 single-dose trials; 66 participants). Analyses of tolerability and safety were not possible for these studies. There was low-certainty evidence that CBD oil did not add value to specialist palliative care alone in the reduction of pain intensity in people with advanced cancer. There was no difference in the number of dropouts due to adverse events and serious adverse events (1 study, 144 participants, qualitative analysis). We found no studies using herbal cannabis.

AUTHORS' CONCLUSIONS

There is moderate-certainty evidence that oromucosal nabiximols and THC are ineffective in relieving moderate-to-severe opioid-refractory cancer pain. There is low-certainty evidence that nabilone is ineffective in reducing pain associated with (radio-) chemotherapy in people with head and neck cancer and non-small cell lung cancer. There is low-certainty evidence that a single dose of synthetic THC analogues is not superior to a single low-dose morphine equivalent in reducing moderate-to-severe cancer pain. There is low-certainty evidence that CBD does not add value to specialist palliative care alone in the reduction of pain in people with advanced cancer.

Heterosynaptic long-term potentiation of non-nociceptive synapses requires endocannabinoids, NMDARs, CamKII, and PKCζ

Noxious stimuli or injury can trigger long-lasting sensitization to non-nociceptive stimuli (referred to as allodynia in mammals). Long-term potentiation (LTP) of nociceptive synapses has been shown to contribute to nociceptive sensitization (hyperalgesia) and there is even evidence of heterosynaptic spread of LTP contributing to this type of sensitization. This study will focus on how activation of nociceptors elicits heterosynaptic LTP (hetLTP) in non-nociceptive synapses. Previous studies in the medicinal leech (Hirudo verbana) have demonstrated that high-frequency stimulation (HFS) of nociceptors produces both homosynaptic LTP as well as hetLTP in non-nociceptive afferent synapses. This hetLTP involves endocannabinoid-mediated disinhibition of non-nociceptive synapses at the presynaptic level, but it is not clear if there are additional processes contributing to this synaptic potentiation. In this study, we found evidence for the involvement of postsynaptic level change and observed that postsynaptic N-methyl-d-aspartate (NMDA) receptors (NMDARs) were required for this potentiation. Next, Hirudo orthologs for known LTP signaling proteins, CamKII and PKCζ, were identified based on sequences from humans, mice, and the marine mollusk Aplysia. In electrophysiological experiments, inhibitors of CamKII (AIP) and PKCζ (ZIP) were found to interfere with hetLTP. Interestingly, CamKII was found to be necessary for both induction and maintenance of hetLTP, whereas PKCζ was only necessary for maintenance. These findings show that activation of nociceptors can elicit a potentiation of non-nociceptive synapses through a process that involves both endocannabinoid-mediated disinhibition and NMDAR-initiated signaling pathways.NEW & NOTEWORTHY Pain-related sensitization involves increases in signaling by non-nociceptive sensory neurons. This can allow non-nociceptive afferents to have access to nociceptive circuitry. In this study, we examine a form of synaptic potentiation in which nociceptor activity elicits increases in non-nociceptive synapses. This process involves endocannabinoids, "gating" the activation of NMDA receptors, which in turn activate CamKII and PKCζ. This study provides an important link in how nociceptive stimuli can enhance non-nociceptive signaling related to pain.

Medical Cannabis Alleviates Chronic Neuropathic Pain Effectively and Sustainably without Severe Adverse Effect: A Retrospective Study on 99 Cases

Introduction

Medical cannabis may provide a treatment option for chronic neuropathic pain. However, empirical disease-specific data are scarce.

Methods

This is a retrospective observational study including 99 patients with chronic neuropathic pain. These patients received medical cannabis by means of inhaling dried flowers with tetrahydrocannabinol content of <12-22% at a maximal daily dose of 0.15-1 g. Up to six follow-ups were carried out at intervals of 4-6 weeks. Pain severity, sleep disturbance, general improvement, side effects, and therapy tolerance at the follow-up consultations were assessed in interviews and compared with the baseline data using non-parametric Wilcoxon signed-rank test.

Results

Within 6 weeks on the therapy, median of the pain scores decreased significantly from 7.5 to 4.0 (p < 0.001). The proportion of patients with severe pain (score >6) decreased from 96% to 16% (p < 0.001). Sleep disturbance was significantly improved with the median of the scores decreased from 8.0 to 2.0 (p < 0.001). These improvements were sustained over a period of up to 6 months. There were no severe adverse events reported. Mild side effects reported were dryness in mucous tissue (5.4%), fatigue (4.8%), and increased appetite (2.7%). Therapy tolerance was reported in 91% of the interviews.

Conclusion

Medical cannabis is safe and highly effective for treating neuropathic pain and concomitant sleep disturbance.

Opinions towards Medical Students' Self-Care and Substance Use Dilemmas-A Future Concern despite a Positive Generational Effect?

This study examines demographic factors which may influence opinions concerning medical students' self-care and substance use behaviors as a means of providing insights into how future doctors view these issues compared to Australian doctors and members of the public. We conducted national, multicenter, prospective, on-line cross-sectional surveys using hypothetical scenarios to three cohorts- Australian medical students, medical doctors, and the public. Participants' responses were compared for the different contextual variables within the scenarios and the participants' demographic characteristics. In total 2602 medical students, 809 doctors and 503 members of the public participated. Compared with doctors and the public, medical students were least tolerant of alcohol intoxication, and most tolerant of using stimulants to assist with study, and cannabis for anxiety. Doctor respondents more often aligned with the public's opinions on the acceptability of the medical students' behaviors. Although opinions are not equivalent to behaviour, Australian students' views on the acceptability for cannabis to help manage anxiety, and inappropriate use of prescription-only drugs are concerning; these future doctors will be responsible for prescribing drugs and managing patients with substance abuse problems. However, if current Australian medical student's opinions on alcohol misuse persist, one of the commonest substance addictions amongst doctors may decrease in future.

Pharmacologic Management of Persistent Pain in Cancer Survivors

Improvements in screening, diagnosis and treatment of cancer has seen cancer mortality substantially diminish in the past three decades. It is estimated there are almost 20 million cancer survivors in the USA alone, but some 40% live with chronic pain after completing treatment. While a broad definition of survivorship that includes all people living with, through and beyond a cancer diagnosis—including those with active cancer—is often used, this narrative review primarily focuses on the management of pain in people who are disease-free after completing primary cancer treatment as adults. Chronic pain in this population needs a different approach to that used for people with a limited prognosis. After describing the common chronic pain syndromes caused by cancer treatment, and the pathophysiologic mechanisms involved, the pharmacologic management of entities such as post-surgical pain, chemotherapy-induced neuropathy, aromatase inhibitor musculoskeletal syndrome and checkpoint inhibitor-related pain are described. The challenges  associated with opioid prescribing in this population are given special attention. Expert guidelines on pain management in cancer survivors now recommend a combination of pharmacologic and non-pharmacologic modalities, and these are also briefly covered.

Cannabis-Based Medicines and Medical Cannabis for Chronic Neuropathic Pain

Neuropathic pain represents a broad category of pain syndromes that include a wide variety of peripheral and central disorders. The overall prevalence of neuropathic pain in the general population is reported to be between 7 and 10%. Management of neuropathic pain presents an unmet clinical need, with less than 50% of patients achieving substantial pain relief with medications currently recommended such as pregabalin, gabapentin, duloxetine and various tricyclic antidepressants. It has been suggested that cannabis-based medicines (CbMs) and medical cannabis (MC) may be a treatment option for those with chronic neuropathic pain. CbMs/MC are available in different forms: licensed medications or medical products (plant-derived and/or synthetic products such as tetrahydrocannabinol or cannabidiol); magistral preparations of cannabis plant derivatives with defined molecular content such as dronabinol (tetrahydrocannabinol); and herbal cannabis with a defined content of tetrahydrocannabinol and/or cannabidiol, together with other active ingredients (phytocannabinoids other than cannabidiol/tetrahydrocannabinol, terpenes and flavonoids). The availability of different types of CbMs/MC varies between countries worldwide. Systematic reviews of available randomised controlled trials have stated low-quality evidence for CbMs and MC for chronic neuropathic pain. Depending on the studies included in the various quantitative syntheses, authors have reached divergent conclusions on the efficacy of CbMs/MC for chronic neuropathic pain (from not effective to a clinically meaningful benefit). Clinically relevant side effects of CbMs/MC, especially for central nervous system and psychiatric disorders, have been reported by some systematic reviews. Recommendations for the use of CbMs/MC for chronic neuropathic pain by various medical associations also differ, from negative recommendations, no recommendation possible, recommended as third-line therapy, or recommended as an alternative in selected cases failing standard therapies within a multimodal concept. After reading this paper, readers are invited to formulate their own conclusions regarding the potential benefits and harms of CbMs/MC for the treatment of chronic neuropathic pain.

Possible opioid-saving effect of cannabis-based medicine using individual-based data from the Norwegian Prescription Database

Some ecological studies have shown that areas with higher use of cannabis may have lower opioid use and fewer opioid-related problems. Newer studies are questioning this finding. Few individually based studies have been performed. Using data from the Norwegian Prescription Database, this study investigated the individual level effect of prescribed cannabis extract (Sativex®) in prescription opioid users on their opioid use in the following year. Looking at all those filling a prescription for Sativex®, opioid use was only marginally lowered in the follow-up period. Some Sativex® users, however, filled more prescriptions for Sativex® and were able to reduce their opioid use substantially. Further studies are needed to elucidate more details on these patients, so as to know who can benefit from such cannabis-based extracts in reducing their opioid use.

International Association for the Study of Pain Presidential Task Force on Cannabis and Cannabinoid Analgesia: research agenda on the use of cannabinoids, cannabis, and cannabis-based medicines for pain management

ABSTRACT

The President of the International Association for the Study of Pain established a task force on cannabis and cannabinoid analgesia to systematically examine the evidence on (1) analgesic pharmacology of cannabinoids and preclinical evidence on their efficacy in animal models of injury-related or pathological persistent pain; (2) the clinical efficacy of cannabis, cannabinoids, and cannabis-based medicines for pain; (3) harms related to long-term use of cannabinoids; as well as (4) societal issues and policy implications related to the use of these compounds for pain management. Here, we summarize key knowledge gaps identified in the task force outputs and propose a research agenda for generating high-quality evidence on the topic. The systematic assessment of preclinical and clinical literature identified gaps in rigor of study design and reporting across the translational spectrum. We provide recommendations to improve the quality, rigor, transparency, and reproducibility of preclinical and clinical research on cannabis and cannabinoids for pain, as well as for the conduct of systematic reviews on the topic. Gaps related to comprehensive understanding of the endocannabinoid system and cannabinoid pharmacology, including pharmacokinetics and drug formulation aspects, are discussed. We outline key areas where high-quality clinical trials with cannabinoids are needed. Remaining important questions about long-term and short-term safety of cannabis and cannabinoids are emphasized. Finally, regulatory, societal, and policy challenges associated with medicinal and nonmedicinal use of cannabis are highlighted, with recommendations for improving patient safety and reducing societal harms in the context of pain management.

A Multicriteria Decision Analysis Comparing Pharmacotherapy for Chronic Neuropathic Pain, Including Cannabinoids and Cannabis-Based Medical Products

Background:

Pharmacological management of chronic neuropathic pain (CNP) still represents a major clinical challenge. Collective harnessing of both the scientific evidence base and clinical experience (of clinicians and patients) can play a key role in informing treatment pathways and contribute to the debate on specific treatments (e.g., cannabinoids). A group of expert clinicians (pain specialists and psychiatrists), scientists, and patient representatives convened to assess the relative benefit–safety balance of 12 pharmacological treatments, including orally administered cannabinoids/cannabis-based medicinal products, for the treatment of CNP in adults.

Methods:

A decision conference provided the process of creating a multicriteria decision analysis (MCDA) model, in which the group collectively scored the drugs on 17 effect criteria relevant to benefits and safety and then weighted the criteria for their clinical relevance.

Findings:

Cannabis-based medicinal products consisting of tetrahydrocannabinol/cannabidiol (THC/CBD), in a 1:1 ratio, achieved the highest overall score, 79 (out of 100), followed by CBD dominant at 75, then THC dominant at 72. Duloxetine and the gabapentinoids scored in the 60s, amitriptyline, tramadol, and ibuprofen in the 50s, methadone and oxycodone in the 40s, and morphine and fentanyl in the 30s. Sensitivity analyses showed that even if the pain reduction and quality-of-life scores for THC/CBD and THC are halved, their benefit–safety balances remain better than those of the noncannabinoid drugs.

Interpretation:

The benefit–safety profiles for cannabinoids were higher than for other commonly used medications for CNP largely because they contribute more to quality of life and have a more favorable side effect profile. The results also reflect the shortcomings of alternative pharmacological treatments with respect to safety and mitigation of neuropathic pain symptoms. Further high-quality clinical trials and systematic comprehensive capture of clinical experience with cannabinoids is warranted. These results demonstrate once again the complexity and multimodal mechanisms underlying the clinical experience and impact of chronic pain.