Test-retest reliability of the underlying latent factor structure of alcohol subjective response

RATIONALE

Alcohol subjective experiences are multi-dimensional and demonstrate wide inter-individual variability. Recent efforts have sought to establish a clearer understanding of subjective alcohol responses by identifying core constructs derived from multiple measurement instruments.

OBJECTIVE

The aim of this study was to evaluate the temporal stability of this approach to conceptualizing alcohol subjective experiences across successive alcohol administrations in the same individuals.

METHODS

Healthy moderate alcohol drinkers (n = 104) completed six experimental sessions each, three with alcohol (0.8 g/kg), and three with a non-alcoholic control beverage. Participants reported subjective mood and drug effects using standardized questionnaires before and at repeated times after beverage consumption. We explored the underlying latent structure of subjective responses for all alcohol administrations using exploratory factor analysis and then tested measurement invariance over the three successive administrations using multi-group confirmatory factor analyses.

RESULTS

Exploratory factor analyses on responses to alcohol across all administrations yielded four factors representing "Positive mood," "Sedation," "Stimulation/Euphoria," and "Drug effects and Urges." A confirmatory factor analysis on the separate administrations indicated acceptable configural and metric invariance and moderate scalar invariance.

CONCLUSIONS

In this study, we demonstrate temporal stability of the underlying constructs of subjective alcohol responses derived from factor analysis. These findings strengthen the utility of this approach to conceptualizing subjective alcohol responses especially for use in prospective and longitudinal alcohol challenge studies relating subjective response to alcohol use disorder risk.

[Therapy in heroin addiction]

Heroin addiction is one of the most devastating and expensive of public health problems. The most effective treatment is opioid replacement therapy. Replacement of heroin, a short-acting euphoriant with methadone or other opioids that have significantly longer duration of action provides a number of therapeutic benefits. Opioid detoxification has a role in both preventing acute withdrawal and maintaining long-term abstinence. Opioid-based detoxification is based on the principle of cross-tolerance, in which one opioid is replaced with another one that is slowly tapered. For the treatment of heroin addicts a wide range of psychosocial and pharmacotherapeutic treatments are available; of these, methadone maintenance therapy has the most evidence of benefit. Methadone maintenance reduces and/or eliminates the use of heroin, reduces the death rate and criminality associated with heroin use, and allows patients to improve their health and social productivity. In addition, enrollment in methadone maintenance has the potential to reduce the transmission of infectious diseases associated with heroin injection, such as hepatitis and HIV. The principal effects of methadone maintenance are to relieve narcotic craving, suppress the abstinence syndrome, and block the euphoric effects associated with heroin. There is growing interest in expanding treatment into primary care, allowing opioid addiction to be managed like other chronic illnesses. Buprenorphine which is a long-acting partial agonist was also approved as pharmacotherapy for opioid dependence. Opioid antagonists can reduce heroin self-administration and opioid craving in detoxified addicts. Naltrexone, which is a long-acting competitive antagonist at the opioid receptors, blocks the subjective and objective responses produced by intravenous opioids. Naltrexone is employed to accelerate opioid detoxification by displacing heroin and as a maintenance agent for detoxified formerly heroin-dependent patients who want to remain opioid-free.

Neuronal oscillations and functional interactions between resting state networks

Functional magnetic imaging (fMRI) studies showed that resting state activity in the healthy brain is organized into multiple large-scale networks encompassing distant regions. A key finding of resting state fMRI studies is the anti-correlation typically observed between the dorsal attention network (DAN) and the default mode network (DMN), which - during task performance - are activated and deactivated, respectively. Previous studies have suggested that alcohol administration modulates the balance of activation/deactivation in brain networks, as well as it induces significant changes in oscillatory activity measured by electroencephalography (EEG). However, our knowledge of alcohol-induced changes in band-limited EEG power and their potential link with the functional interactions between DAN and DMN is still very limited. Here we address this issue, examining the neuronal effects of alcohol administration during resting state by using simultaneous EEG-fMRI. Our findings show increased EEG power in the theta frequency band (4-8 Hz) after administration of alcohol compared to placebo, which was prominent over the frontal cortex. More interestingly, increased frontal tonic EEG activity in this band was associated with greater anti-correlation between the DAN and the frontal component of the DMN. Furthermore, EEG theta power and DAN-DMN anti-correlation were relatively greater in subjects who reported a feeling of euphoria after alcohol administration, which may result from a diminished inhibition exerted by the prefrontal cortex. Overall, our findings suggest that slow brain rhythms are responsible for dynamic functional interactions between brain networks. They also confirm the applicability and potential usefulness of EEG-fMRI for central nervous system drug research.

Opioid abusers' ability to differentiate an opioid from placebo in laboratory challenge testing

BACKGROUND

Abuse liability assessments influence drug development, federal regulation, and clinical care. One suggested procedure to reduce variability of assessments is a qualification phase, which assesses whether study applicants adequately distinguish active drug from placebo; applicants failing to make this distinction are disqualified. The present analyses assessed differences between qualification phase qualifiers and non-qualifiers.

METHODS

Data were collected from 23 completers of the qualification phase of an abuse liability study. Opioid abusing participants received 30 mg oxycodone and placebo orally on separate days, and were characterized as qualifiers (vs. non-qualifiers) if their peak visual analog scale liking rating for oxycodone was at least 20 points higher than placebo's peak rating. Groups were compared on demographic characteristics, drug history, and physiologic, subject and observer ratings.

RESULTS

61% of participants were qualifiers and 39% were non-qualifiers. Groups had similar demographic characteristics, drug use histories, and pupillary constriction responses. However, unlike qualifiers, non-qualifiers had an exaggerated placebo response for the liking score (p=0.03) and an attenuated oxycodone response for the liking score (p<0.0001). Non-qualifiers' failure to differentiate oxycodone versus placebo was evident for subject and observer ratings.

CONCLUSION

Different subjective responses to identical stimuli support the use of a qualification phase in abuse liability assessments. Further research should explore objective measures that may better account for these differences, determine optimal qualification criteria, and explore the developmental course of drug use. This study also documents certain opioid abusers fail to differentiate 30 mg of oxycodone from placebo, a phenomenon deserving further study.

Mephenesin: abuse and dependence

Mephenesin is a muscle relaxant with poorly documented clinical value. Its sedative properties have been known since its introduction on the French market. Cases of abuse and dependence have been reported, particularly since the early 2010s. Some adults were reported to be taking up to 12 g of mephenesin per day, the equivalent of an entire box. Most of them had a history of dependence on various other psychotropic drugs. Withdrawal symptoms, including tremor, anxiety, and aggression, have been reported in 3 patients. A woman who was taking no other drugs died of bronchial aspiration following mephenesin overdose. Painful muscle spasm is sometimes relieved by a short rest period, or paracetamol. Repeated requests for mephenesin should alert health professionals to the possibility of abuse. It is best to avoid mephenesin altogether, especially when the patient has a history of abuse or dependence.

Amphetamine induced dopamine release increases anxiety in individuals recovered from anorexia nervosa

OBJECTIVE

Genetic, pharmacologic, and physiological data suggest that individuals with anorexia nervosa (AN) have altered striatal dopamine (DA) function.

METHOD

We used an amphetamine challenge and positron emission tomography [(11) C]raclopride paradigm to explore DA striatal transmission in 10 recovered (REC) AN compared with 9 control women (CW).

RESULTS

REC AN and CW were similar for baseline, postamphetamine [(11) C]raclopride binding potential (BP(ND) ) and change (Δ) in BP(ND) for all regions. In CW, ventral striatum Δ BP(ND) was associated with euphoria (r = -0.76; p = 0.03), which was not found for REC AN. Instead, REC AN showed a significant relationship between anxiety and Δ BP(ND) in the precommissural dorsal caudate (r = -0.62, p = 0.05).

DISCUSSION

REC AN have a positive association between endogenous DA release and anxiety in the dorsal caudate. This finding could explain why food-related DA release produces anxiety in AN, whereas feeding is pleasurable in healthy participants.

Effect of d-amphetamine on post-error slowing in healthy volunteers

RATIONALE

Post-error slowing has long been considered a sign of healthy error detection and an important component of cognitive function. However, the neuropharmacological processes underlying post-error slowing are poorly understood.

OBJECTIVES

This study investigated the effect of the dopamine agonist d-amphetamine on post-error slowing and secondarily, the potential mediator of drug-induced euphoria and potential moderators of personality and baseline task performance.

METHODS

Healthy male and female participants (N = 110) completed four study sessions, at which d-amphetamine (placebo 5, 10, 20 mg) was administered under double-blind, counter-balanced conditions. At each session, participants completed subjective drug effect assessments and a working memory task (N-back) to measure post-error slowing. They completed the Multidimensional Personality Questionnaire (MPQ) during screening.

RESULTS

Amphetamine (20 mg) reduced post-error slowing, consistent with a dampened behavioral reactivity to errors. This was not related to drug-induced euphoria. Although higher scores on MPQ constraint were related to less post-error slowing under placebo conditions, neither personality nor baseline cognitive performance moderated the effects of amphetamine on post-error slowing.

CONCLUSIONS

The finding that amphetamine reduced post-error slowing supports the idea that dopamine plays a role in error stimulus processing. The finding is discussed in relation to an existing literature on the mechanisms and function of behavioral and electrophysiological indices of error sensitivity.

Weakening of negative relative to positive associations with cocaine-paired cues contributes to cue-induced responding after drug removal

Cocaine has been shown to have initial positive (euphoric) and delayed negative (anxiogenic) effects in both humans and animals. Cocaine-paired cues are consequently imbued with mixed positive and negative associations. The current study examines the relative roles of these dual associations in the enhanced drug-seeking observed upon presentation of cocaine-paired cues. Rats ran a straight alley once/day for a single i.v. injection of cocaine (1.0 mg/kg/inj) in the presence of a distinctive olfactory cue (scented cotton swabs placed under the apparatus). An alternate scent was presented in a separate cage 2-h prior to runway testing. After 15 trials/days, the scents and cocaine reinforcer were removed and a series of extinction trials (lasting for 1 or 3 weeks) was initiated. Immediately following extinction, runway responding was tested during a single trial in the presence of the cocaine-paired or non-paired cue. As previously reported, while subjects initiated responding faster over trials (reduced latencies to leave the start box), they exhibited a progressive increase in approach-avoidance conflict behavior ("retreats") regarding goal-box entry, reflecting cocaine's dual positive+negative effects. Once established, retreat behaviors persisted over the course of 1 or 3 weeks days of extinction. However, both run times and retreats decreased in response to presentation of the cocaine-paired but not the non-paired scent. These data suggest that, after reinforcer removal, cue-induced cocaine-seeking stems in part from a reduction in approach-avoidance conflict; i.e., a greater weakening of the negative relative to the positive associations that animals form with cocaine-paired stimuli.

Positive and negative subjective effects of extended-release oxymorphone versus controlled-release oxycodone in recreational opioid users

OBJECTIVE

To compare the subjective effects of oxymorphone extended release (OM-ER) versus oxycodone controlled release (OC-CR).

DESIGN

Randomized, double-blind, crossover study.

SETTING

Inpatient unit.

SUBJECTS

Healthy, nondependent recreational opioid users.

INTERVENTIONS

Single intact oral tablets that were placebo or contained OM-ER (15 and 30 mg) or OC-CR (30 and 60 mg). Doses were representative of mid-range doses for chronic pain and were calculated using an established opioid conversion table.

MAIN OUTCOME MEASURES

Visual Analog Scales, Subjective Drug Value (SDV), and Addiction Research Center Inventory (ARCI) measured positive, negative, and balance effects and pupillometry. Equianalgesic comparisons were between OM-ER 15 mg versus OC-CR 30 mg (low doses) and OM-ER 30 mg versus OC-CR 60 mg (high doses).

RESULTS

Thirty-five subjects received all five treatments. Positive subjective effects were lower for OM-ER 15 mg versus OC-CR 30 mg and for OM-ER 30 mg versus OC-CR 60 mg in ARCI Morphine Benzedrine Group (< or = 0.01 for both), Good Effects (p < 0.001 for both), Rush (p < 0.001 for both), and High VAS (p < 0.001 for both). Nausea was higher with OC-CR (p < or = 0.02), and Bad Effects were higher for OC-CR 60 mg versus OM-ER 30 mg (p < 0.001). Balance effects were lower for OM-ER versus OC-CR (Drug Liking, p < 0.001; Overall Drug Liking, p < or = 0.006; SDV, p < or = 0.008), except for Take Drug Again (p < 0.001 for OC-CR 30 mg versus OM-ER 15 mg; p = 0.18 for high-dose group). Euphoric mood, nausea, somnolence, vomiting, and dizziness were more common with OC-CR than OM-ER.

LIMITATIONS

Single-dose design; use of healthy, recreational opioid users.

CONCLUSIONS

At equianalgesic doses, single oral intact OM-ER produced lower positive, negative, and balance subjective effects than OC-CR, indicating that analgesic potency may not necessarily be reflected in subjective/objective effects.

[Heroin addiction]

Heroin is an illicit, highly addictive drug. It is either the most abused or the most rapidly acting member of opioids. Abusers describe a feeling of a surge of pleasurable sensation, named as "rush" or "high". Repeated administration of high doses of heroin results in the induction of physical dependence. Physical dependence refers to an altered physiological state produced by chronic administration of heroin which necessitates the continued administration of the drug to prevent the appearance of a characteristic syndrome, the opioid withdrawal or abstinence syndrome. Withdrawal symptoms may occur within a few hours after the last administration of heroin. Symptoms of the withdrawal include restlessness, insomnia, drug craving, diarrhea, muscle and bone pain, cold flashes with goose bumps, and leg movements. Major withdrawal symptoms peak between 48 and 72 hours after the last dose of heroin and subside after about a week. At this time, weakness and depression are pronounced and nausea and vomiting are common. Nevertheless, some chronic addicts have shown persistent withdrawal signs for many months or even years. Heroin addiction is considered as a behavioural state of compulsive drug use and a high tendency to relapse after periods of abstinence. It is generally accepted that compulsive use and relapse are typically associated with the status of heroin craving or heroin hunger that are difficult to define but appear to be powerful motivational significance in the addiction process. The route of administering heroin varies largely and may indicate the degree of seriousness of the individual's addiction. Intravenous administration seems to be the predominant method of heroin use, but recently a shift in heroin use pattern has been found, i.e. from injection to sniffing and smoking. Frequent injections coupled with widespread sharing of syringes increase the risk of contracting HIV, hepatitis B, C and other blood-borne infectious diseases. Long-term use of heroin has also severe medical consequences such as scarred veins, bacterial infections of blood vessels, liver and kidney diseases, and lung complications.

Phenomenology of adolescent inhalant intoxication

Although volatile substance inhalation is prevalent in many contexts and presents a serious threat to public health, this pernicious form of substance misuse remains poorly understood. The question of why people seek and misuse inhalants may be addressed by examining phenomenological accounts of inhalant intoxication, yet few investigations of inhalant intoxication experiences are reported in the literature. This investigation employed a structured interview to assess inhalant intoxication experiences of 267 low-, moderate-, and high-frequency inhalant users. Low-frequency inhalant users reported predominately hedonic experiences during inhalant intoxication, whereas high-frequency users reported a mixture of hedonic and aversive experiences. Aversive experiences such as depressed mood, suicidal ideation, and chest pain were commonly reported by high-frequency users but were relatively rare among low-frequency users. High-frequency users also experienced significantly more euphoria, talkativeness, and grandiosity during inhalant intoxication than low-frequency users. Hedonic and aversive experiences during episodes of inhalant intoxication are relatively common among high-frequency adolescent inhalant users.

Behavioral evidence for the significance of serotoninergic (5-HT) receptors in cocaine addiction

Cocaine addiction has somatic, psychological, psychiatric, socio-economic and legal implications in the developed world. Presently, there is no medication approved for the treatment of cocaine addiction. In recent years, data from the literature (pre-clinical studies and clinical trials) have provided several lines of evidence that serotonin (5-HT) and 5-HT receptors play a modulatory role in the mechanisms of action of cocaine. Here we review the contribution of 5-HT receptor subtypes to cocaine sensitization, discrimination, conditioned place preference, self-administration, reinstatement of seeking behavior and withdrawal symptoms in laboratory animals. Additionally, the consequences of chronic cocaine exposure on particular 5-HT receptor-assigned functions in pre-clinical studies are presented.

[Successful quetiapine therapy in psychotic patients with mood elevation]

Antipsychotics have been used in the therapy of schizophrenia and bipolar disorder and several second generation antipsychotics (SGA) are already available in Hungary. The clinical trials' results are confusing in regarding the differences in the efficacy of the SGA's, but the differences in their side-effects are clear. Considering its most important side-effects, such as extrapyramidal symptoms, weight gain, metabolic syndrome and prolactin level elevation, quetiapine has a fairly good side effect profile, and can therefore be recommended especially in case of bipolar patients who are highly sensitive towards side effects.. In our case-report, we present four patients who were successfully treated with quetiapine for their psychotic mood elevation.

The relative abuse liability of oral oxycodone, hydrocodone and hydromorphone assessed in prescription opioid abusers

Abuse of prescription opioids has risen precipitously in the United States. Few controlled comparisons of the abuse liability of the most commonly abused opioids have been conducted. This outpatient study employed a double-blind, randomized, within-subject, placebo-controlled design to examine the relative abuse potential and potency of oral oxycodone (10, 20 and 40 mg), hydrocodone (15, 30 and 45 mg), hydromorphone (10, 17.5 and 25mg) and placebo. Healthy adult volunteers (n=9) with sporadic prescription opioid abuse participated in 11 experimental sessions (6.5h in duration) conducted in a hospital setting. All three opioids produced a typical mu opioid agonist profile of subjective (increased ratings of liking, good effects, high and opiate symptoms), observer-rated, and physiological effects (miosis, modest respiratory depression, exophoria and decrements in visual threshold discrimination) that were generally dose-related. Valid relative potency assays revealed that oxycodone was roughly equipotent to or slightly more potent than hydrocodone. Hydromorphone was only modestly more potent (less than two-fold) than either hydrocodone or oxycodone, which is inconsistent with prior estimates arising from analgesic studies. These data suggest that the abuse liability profile and relative potency of these three commonly used opioids do not differ substantially from one another and suggest that analgesic potencies may not accurately reflect relative differences in abuse liability of prescription opioids.

Tolerability and effects of oral Delta9-tetrahydrocannabinol in older adolescents with marijuana use disorders

OBJECTIVE

The tolerability and effects of oral Delta9-tetrahydrocannabinol (THC) have been previously investigated in adult marijuana abusers. However, no studies have included adolescent participants. This double-blind laboratory study investigated the tolerability and effects of oral THC in a group of older adolescents with marijuana use disorders.

METHODS

Eight participants (ages 16-21 years), smoking an average of 5.2 days/week and 2.5 "joints"/day, completed this four-session study, during which they received one of four oral THC doses (0, 2.5, 5, 10 mg) each session. Administration of oral THC doses was counterbalanced across participants. During each session, participants completed the Digit-Symbol Substitution Task (DSST) and subjective-effect ratings at baseline and 1, 2, and 3 h after oral THC administration.

RESULTS

Oral THC (5 mg and 10 mg) increased several "positive" subjective-effect ratings (e.g., "Good Drug Effect"), while producing no significant effects on cardiovascular measures, DSST performance, or "negative" subjective-effect ratings.

CONCLUSIONS

These results indicate that oral THC was well tolerated and suggest further study of this medication in adolescent marijuana abusers.

Beta-endorphin and drug-induced reward and reinforcement

Although drugs of abuse have different acute mechanisms of action, their brain pathways of reward exhibit common functional effects upon both acute and chronic administration. Long known for its analgesic effect, the opioid beta-endorphin is now shown to induce euphoria, and to have rewarding and reinforcing properties. In this review, we will summarize the present neurobiological and behavioral evidences that support involvement of beta-endorphin in drug-induced reward and reinforcement. Currently, evidence supports a prominent role for beta-endorphin in the reward pathways of cocaine and alcohol. The existing information indicating the importance of beta-endorphin neurotransmission in mediating the reward pathways of nicotine and THC, is thus far circumstantial. The studies described herein employed diverse techniques, such as biochemical measurements of beta-endorphin in various brain sites and plasma, and behavioral measurements, conducted following elimination (via administration of anti-beta-endorphin antibodies or using mutant mice) or augmentation (by intracerebral administration) of beta-endorphin. We suggest that the reward pathways for different addictive drugs converge to a common pathway in which beta-endorphin is a modulating element. Beta-endorphin is involved also with distress. However, reviewing the data collected so far implies a discrete role, beyond that of a stress response, for beta-endorphin in mediating the substance of abuse reward pathway. This may occur via interacting with the mesolimbic dopaminergic system and also by its interesting effects on learning and memory. The functional meaning of beta-endorphin in the process of drug-seeking behavior is discussed.

Assessment of differential doses of buprenorphine for long term pharmacotherapy among opiate dependent subjects

The aim of the present study was to evaluate, two different doses of sublingual buprenorphine (2 mg and 4 mg) among patients on maintenance treatment and to assess the relationship of steady state plasma level with craving. Twenty three male opioid dependent (ICD-10 DCR) subjects, were assigned to double blind randomized controlled trial of 2 and 4 mg/day doses of buprenorphine in an inpatient setting. They were evaluated thrice (2nd, 7th and 14th day) in 2 weeks for withdrawal symptoms (acute and protracted), sedation, euphoria, craving, side effects, global rating of well being and for measurement of plasma levels of buprenorphine. The data showed that there were no significant difference in scores of euphoria and sedation, protracted withdrawal symptoms and side effects, craving and overall well being and plasma level of buprenorphine among the subjects. However, both the groups had significant difference in score on almost all the measurements on final observation in comparison to initial observation. Both 2 mg/day and 4 mg/day dose of buprenorphine were effective in long term pharmacotherapy of opioid dependence without significant difference as compared by different measures used in the study.

Effects of environmental enrichment and paradoxical sleep deprivation on open-field behavior of amphetamine-treated mice

BACKGROUND

Environmental enrichment or paradoxical sleep deprivation (PSD) has been shown to modify some responses elicited by drugs of abuse. The aims of the present study were to examine the effects of environmental enrichment and PSD, conducted separately or in association, on open-field behavior elicited by amphetamine (AMP) in mice.

METHODS

Male C57BL/6 mice were randomly assigned to live in either an enriched environmental condition (EC) or a standard environmental condition (SC) for 12 months since weaning. Some of the EC and SC mice were sleep deprived for 48 h, while others were maintained in their home-cages. Immediately after PSD or home-cage stay, the animals received an ip injection of saline, 2.5 mg/kg AMP or 5.0 mg/kg AMP. Fifteen minutes later, their open-field behavior was quantified.

RESULTS

Whereas PSD enhanced total and peripheral locomotor activity of acutely AMP-treated mice, environmental enrichment presented only a trend toward enhancement. When PSD and environmental enrichment were combined, an increase in the total and peripheral locomotion frequencies of AMP-treated animals, similar to that observed after PSD, was revealed. In addition, PSD, environmental enrichment or their combination did not modify the effects of AMP on the other open-field behavioral parameters that were analyzed.

CONCLUSION

The present findings demonstrate that some (but not all) of the behavioral effects caused by AMP acute administration can be similarly and specifically enhanced by both environmental enrichment and PSD in C57BL/6 mice.

Pharmacological treatment of acute mania in psychiatric in-patients between 1994 and 2004

BACKGROUND

In a cross-section approach we investigated prescription practice in acute mania in 63 German, Swiss and Austrian hospitals between 1994 and 2004.

METHODS

Our data were gathered from a large drug safety program (AMSP) within which on two reference days each year all administered drugs are recorded. For the present study, all cases with a primary diagnosis of acute euphoric mania (n=1291) or mixed-state mania (n=143) were identified. Prescription rates from two periods, 1994 to 1999 and 2000 to 2004, were compared.

RESULTS

In euphoric mania, prescription of lithium decreased by about one-fifth (43.3% to 34.5%, p<0.01), while prescription of anticonvulsants increased by one-half (from 40.0% to 60.7%, p<0.001). Administration of atypical antipsychotics more than doubled (18.5% to 43.9%, p<0.001), while use of typical antipsychotics decreased significantly (56.9% to 27.8%, p<0.001). Overall prescription rates of antipsychotics (79.6% vs. 81.6%) and antidepressants (14.0% vs. 15.5%) remained stable, while administration of tranquilizers increased significantly (26.3% to 34.3%, p<0.01). In mixed-state mania, similar trends over time to those seen in euphoric mania were observed for lithium (43.2% to 33.3%), anticonvulsants (50.0% to 69.7%, p<0.05) and tranquilizers (22.7% to 40.4%). Prescription rates of antipsychotics slightly increased (63.6% to 72.7%), while prescription of antidepressants slightly decreased (54.5% to 46.5%). Polypharmacy was a common phenomenon: patients with euphoric mania were treated with a mean number of 2.9+/-1.2 psychotropic agents, and patients with mixed-state mania with 3.3+/-1.5 psychotropic agents. Both groups showed a significant increase over time. Second-generation atypical antipsychotics were adopted quite rapidly for the treatment of acute mania considering the availability of the scientific evidence at that time. Off-label use was a common phenomenon. Deviations from recommended guidelines were found mainly in the use of antidepressant and antipsychotic drugs both in mixed-state and euphoric mania.

CONCLUSIONS

Naturalistic prescription studies like this may encourage a critical scrutiny of clinical treatment habits and may also drive further research thus moderating potential differences between evidence-based knowledge and everyday clinical practice.

Euphoriant effects of nicotine in smokers: fact or artifact?

RATIONALE

The claim that nicotine in cigarettes is euphoriant to smokers is largely based on two studies (Pomerleau and Pomerleau, Psychopharmacology, 108:460-465, 1992; Tobacco Control, 3:374, 1994) in which smokers were instructed to respond to sensations of rush, buzz, or high while smoking low-nicotine or regular cigarettes. However, the assumption that these sensations are pleasurable was not tested and may have biased the results.

OBJECTIVES

The aim of this study was to re-examine the claim that smoked nicotine is euphoriant to smokers.

METHODS

Study 1 surveyed the frequency and pleasantness of the smoking-related sensations of rush, buzz, and high in a sample of smokers. Study 2 replicated Pomerleau and Pomerleau (Psychopharmacology, 108:460-465, 1992) with two sets of instruction. One set, as in the original study, defined these sensations as pleasurable, whereas the other defined them as unpleasant.

RESULTS

Study 1 found that whereas rush and high were perceived as pleasant, buzz was unpleasant to most smokers. Study 2 found that under both sets of instructions, smokers reported more sensations when smoking the regular, as compared to the low-nicotine cigarette. Additionally, the sensations of rush, buzz, and high were rated as more pleasant under the pleasant instructions as compared to the unpleasant instructions. Finally, in the pleasant instructions condition, many participants reported having pressed the button to indicate a pleasurable sensation despite having actually experienced that sensation as unpleasant.

CONCLUSIONS

Our results suggest that the findings of Pomerleau and Pomerleau (Psychopharmacology, 108:460-465, 1992; Tobacco Control, 3:374, 1994) may have been biased by the experimental instructions and cannot be taken as evidence that smoked nicotine is euphoriant to smokers.

Gabapentin does not reduce smoked cocaine self-administration: employment of a novel self-administration procedure

Previously, we reported that gabapentin, a nonselective gamma-aminobutyric acid agonist, reduced 'positive' subjective effects of cocaine without reducing cocaine self-administration. We speculated that the self-administration procedure used in that study was not sensitive to subtle shifts in the reinforcing effects of cocaine. Thus, this study examined the effects of gabapentin maintenance on cocaine self-administration using a purchase-cocaine choice procedure. During this 48-day inpatient/outpatient study, nontreatment-seeking cocaine abusers (n = 12) were maintained on gabapentin (0, 600, 1200 mg/day); four doses of cocaine (0, 12, 25, 50 mg) were each tested twice under each gabapentin condition. All cocaine testing was conducted while participants were inpatients. Before the start of each session, participants were provided with 25 dollars (five 5 dollar bills, one for each choice opportunity) and smoked the 'sample' cocaine dose once. Subsequently, participants were given five opportunities to purchase the sampled dose of cocaine (at 5 dollars per dose) or to keep 5 dollars for that choice trial. Choice to self-administer cocaine increased significantly with escalating cocaine doses; gabapentin maintenance did not alter choice to self-administer cocaine. These results concur with findings from our previous investigations of gabapentin and with those from a clinical trial examining the effects of larger gabapentin doses on cocaine use by treatment-seeking cocaine-dependent individuals. Together, the data indicate that gabapentin does not show promise as a treatment medication for cocaine dependence.

Does stress reactivity or response to amphetamine predict smoking progression in young adults? A preliminary study

Recent studies with laboratory animals indicate that a constellation of behavioral factors predict progression to self-administer drugs. Relatively little is known about behavioral or biological factors that predict the progression in drug use from initial experimentation to regular use in human drug users. The present exploratory study examined reactivity to an acute stressor and reactivity to a single dose of a dopaminergic drug as predictors in progression to heavier smoking in young cigarette smokers over a 6-month period. Forty-four college students who were light to moderate smokers participated in three laboratory sessions, followed by a follow-up interview 6 months later to determine smoking level. On one of the laboratory sessions subjects underwent the Trier Social Stress Test, and on the others they ingested capsules containing placebo or 20 mg D-amphetamine. Outcome measures included subjective ratings of mood and measures of heart rate and salivary cortisol. We found modest positive relationships between stress reactivity and certain responses to amphetamine. Further, stress-induced increases in cortisol were positively related to increases in cigarette smoking in the 31 subjects who we were able to contact at 6 months. Although these results are highly preliminary, they resemble the relationships previously reported in laboratory animals, suggesting that some of the same factors that predict drug-self-administration in rodents predict progression in drug use among young adults.

Buprenorphine misuse among heroin and amphetamine users in Malmo, Sweden: purpose of misuse and route of administration

Buprenorphine misuse by injecting drug users was assessed in a survey of 350 needle exchangers, either amphetamine (57%) or heroin users (42%). 89% of heroin users and 24% of amphetamine users reported using buprenorphine at some time during the previous year. Most users reported illicit acquisition. Among illicit users, 87% of heroin users reported intake for withdrawal treatment or self-detoxification, and 11% for euphoria. Euphoria seeking was more common among amphetamine users (62%, p < 0.001). Intravenous misuse was reported by 43% of illicit users, and snorting by 29%. Sole sublingual intake was more common among heroin users than among amphetamine users (46 vs. 20%, p < 0.05), and less common among patients reporting euphoria seeking (20 vs. 46%, p < 0.05).

Benztropine pretreatment does not affect responses to acute cocaine administration in human volunteers

Benztropine (Cogentin ) was evaluated for its ability to block cocaine's physiological and subjective effects in humans. In healthy, recreational users of cocaine, placebo, or benztropine (1, 2, and 4 mg orally) was given 2 hr before subjects self-administered 0.9 mg/kg of cocaine intranasally. Measurements were made for 2 hr following cocaine administration, and plasma cocaine and cocaine metabolites were assayed. Cocaine produced typical increases in heart rate and alterations in self-reports measured by visual analog scales (VAS). Benztropine alone did not produce changes on any of these measures. Responses to cocaine with and without benztropine pretreatment were similar: benztropine did not change cocaine's effects. This study of one of the tropane-ring analogs that is approved for human use suggests this compound does not alter cocaine-induced effects, but just as importantly, does not produce any adverse behavioral or physiological effects. The exact therapeutic application of benztropine as a possible adjunct treatment for cocaine abuse in humans require further exploration.

Enhanced sensitivity to the euphoric effects of alcohol in schizophrenia

The purpose of this study was to determine whether schizophrenia was associated with alterations in alcohol response that might explain the elevated risk for AUDs in this population. In a randomized, double-blind, placebo-controlled, counter-balanced 3 test day laboratory study, the effects of alcohol were compared in 23 subjects with schizophrenia (without any previous alcohol use disorder (AUD) but with some alcohol exposure) and in 14 healthy subjects matched for age, gender, education, and lifetime exposure to alcohol. Standard alcohol drinks in a scheduled design were administered to produce blood alcohol levels of 0, 0.02-0.04 mg%, or 0.06-0.08 mg%. Schizophrenia symptoms, perceptual alterations, stimulant and depressant subjective effects of alcohol, and 'high' were measured before alcohol administration and at several post-drug time points. Verbal learning and recall, vigilance and distractibility, and motor function were assessed once per test day. Relative to healthy subjects, subjects with schizophrenia reported greater euphoria and stimulatory effects in response to alcohol. Alcohol produced small transient increases in positive psychotic symptoms and perceptual alterations without affecting negative symptoms. Alcohol also impaired several aspects of immediate and delayed recall, and vigilance, and distractibility. Schizophrenia patients showed increased euphoric and stimulatory responses to alcohol. These exaggerated positive responses to alcohol doses may contribute to the increased risk for AUDs associated with schizophrenia. The absence of 'beneficial' effects of alcohol does not support a self-medication hypothesis of alcohol use in schizophrenia.

Pattern of use and subjective effects of Salvia divinorum among recreational users

BACKGROUND

Salvia divinorum is a member of the Lamiaceae family and contains the psychotropic diterpene and kappa-opioid receptor agonist salvinorin-A. Originally a shamanic inebriant used by the Mexican Mazatec Indians, the plant and its preparations are becoming increasingly popular among non-traditional users.

METHODS

Demographic data and information on pattern of use and subjective effects were obtained by means of self-report questionnaires from a sample of 32 recreational users of salvia and other psychedelics.

RESULTS

Involvement with salvia appeared to be a recent phenomenon. Smoking the extract was the preferred form of administration. Subjective effects were described as intense but short-lived, appearing in less than 1 min and lasting 15 min or less. They included psychedelic-like changes in visual perception, mood and somatic sensations, and importantly, a highly modified perception of external reality and the self, leading to a decreased ability to interact with oneself or with one's surroundings.

CONCLUSIONS

Although some aspects of the subjective effects reported were similar to high doses of classical psychedelics with serotonin-2A receptor agonist activity, the intense derealization and impairment reported appear to be a characteristic of salvia. The observed simultaneous high scores on the LSD and PCAG subscales of the Addiction Research Center Inventory (ARCI) have been previously reported for other kappa-opioid agonists, and support kappa receptor activation as the probable pharmacologic mechanism underlying the modified state of awareness induced by salvia.

Oral hydration, parotid salivation and the perceived pleasantness of small water volumes

Previous studies have suggested that the preference for drinking cold water is increased when the drinker has a dry mouth. In a first experiment, we investigated whether a positive shift in preference would occur for small water volumes (0.75 ml and 1.5 ml) at 8, 16 or 25 degrees C, delivered into a mouth that had been dried using a warmed airflow, versus a normally hydrated mouth. Subjects rated the perceived wetness (or dryness) of their mouth, and the perceived pleasantness (or unpleasantness) of the water samples, using a labeled magnitude scale. Cooler water samples were preferred, and consistent with previous research, this preference was slightly enhanced when the subject's mouth was dried. The coldest water sample led to significantly wetter mouthfeel than the other two less cold samples, consistent with the possibility that the coldest water increased the rate of salivation. However, a second experiment found that although the rate of parotid salivation was increased if the mouth had been dried using a warm airflow, the different water temperatures did not induce different rates of parotid salivation. This indicates that enhanced preference for cold water when the mouth is dry is not invariably based in the reward gained from mouth rewetting via increased parotid saliva flow.

Evaluation of the abuse potential of pagoclone, a partial GABAA agonist

This study assessed the abuse potential of pagoclone, a partial agonist at the gamma-aminobutyric acid type A (GABAA) benzodiazepine receptor site, in healthy recreational drug users. Twenty-three young adults, who reported past recreational use of sedative drugs or alcohol, participated in 4 sessions during which capsules containing pagoclone (doses: 1.2 mg, the higher end of the proposed therapeutic dose range, and 4.8 mg, a 4-fold higher dose), diazepam (dose, 30 mg), or placebo were randomly administered under double-blind conditions. Subjective ratings of mood, drug effects, and psychomotor tests were completed at regular intervals after ingesting the capsules. On most of the standardized measures of abuse potential, pagoclone (dose, 4.8 mg) was rated as being similar to diazepam. Both drugs increased the ratings of good effects and drug liking. However, pagoclone also produced some adverse mood effects that might limit its potential to be used recreationally, and it produced fewer sedativelike effects on some measures. In general, the results with these doses indicate that the abuse potential of pagoclone is similar to that of diazepam, although its profile as a partial agonist suggests that differences between the drugs may emerge at higher doses.

[Investigations concerning the threshold value between endogenous and exogenous GHB (liquid ecstasy)]

The article describes critical investigations concerning the threshold value between endogenous and exogenous concentrations of gamma-hydroxybutyric acid (GHB/"liquid ecstasy") in human blood. The values of GHB in the blood samples of 50 blood donors and 50 postmortem cases were measured with a validated gas-chromatographic/mass-spectrometric procedure according to the guidelines of the GTFCh (Society of Toxicological and Forensic Chemistry). GHB-concentrations were found to range between 0.11 and 1.56 mg/L (mean value 0.54 mg/L/standard deviation 0.37 mg/L/coefficient of variation 68.4 %) in the donors' blood, and between 2.2 and 116 mg/L (mean value 32.4 mg/L/standard deviation 25.6 mg/L/coefficient of variation 79 %) in the postmortem samples, respectively.

Increased frontal and paralimbic activation following ayahuasca, the pan-Amazonian inebriant

RATIONALE

Ayahuasca is a South American psychoactive plant tea which contains the serotonergic psychedelic N,N-dimethyltryptamine (DMT) and monoamine-oxidase inhibitors that render DMT orally active. Previous investigations with ayahuasca have highlighted a psychotropic effect profile characterized by enhanced introspective attention, with individuals reporting altered somatic perceptions and intense emotional modifications, frequently accompanied by visual imagery. Despite recent advances in the study of ayahuasca pharmacology, the neural correlates of acute ayahuasca intoxication remain largely unknown.

OBJECTIVES

To investigate the effects of ayahuasca administration on regional cerebral blood flow.

METHODS

Fifteen male volunteers with prior experience in the use of psychedelics received a single oral dose of encapsulated freeze-dried ayahuasca equivalent to 1.0 mg DMT/kg body weight and a placebo in a randomized double-blind clinical trial. Regional cerebral blood flow was measured 100-110 min after drug administration by means of single photon emission tomography (SPECT).

RESULTS

Ayahuasca administration led to significant activation of frontal and paralimbic brain regions. Increased blood perfusion was observed bilaterally in the anterior insula, with greater intensity in the right hemisphere, and in the anterior cingulate/frontomedial cortex of the right hemisphere, areas previously implicated in somatic awareness, subjective feeling states, and emotional arousal. Additional increases were observed in the left amygdala/parahippocampal gyrus, a structure also involved in emotional arousal.

CONCLUSIONS

The present results suggest that ayahuasca interacts with neural systems that are central to interoception and emotional processing and point to a modulatory role of serotonergic neurotransmission in these processes.

Cocaine craving, euphoria, and self-administration: a preliminary study of the effect of catecholamine precursor depletion

The authors used the acute phenylalanine-tyrosine depletion (APTD) method to test the effect of transient catecholamine precursor depletion on cocaine craving, euphoria, and self-administration. Eight nondependent, nontreatment-seeking cocaine users self-administered 3 doses of cocaine (0.6, 1.5, 3.0 mg/kg, taken intranasally) following ingestion of (a) a nutritionally balanced amino acid mixture, (b) APTD, and (c) APTD followed by L-dopa/carbidopa (2x100 mg/25 mg). APTD decreased both cue and cocaine-induced drug craving but not euphoria or self-administration. APTD+L-dopa also decreased drug craving, possibly reflecting the ability of L-dopa to transiently decrease dopamine cell firing. Together, these preliminary results suggest that the craving elicited by cocaine and cocaine cues is related to changes in catecholamine neurotransmission. Euphoria and the self-administration of freely available drugs by regular users, in comparison, might be better accounted for by other mechanisms.

[Official guidelines for the treatment of acute mania]

There are several national and international practice guidelines on the treatment of acute mania. Their purpose is to assess the available evidence of efficacy for medication used in the treatment of bipolar mania and to grade it according to the quality of studies available. The World Federation of Societies of Biological Psychiatry (WFSBP) has developed such guidelines in 2003. They categorize the scientific quality of the studies into four levels of evidence (A-D) and provide an algorithm based on the degree of severity of the acute manic episode.

Khat (Catha edulis)-an updated review

The habit of chewing fresh leaves and twigs of khat (Catha edulis) for their stimulating amphetamine-like effects is highly prevalent in East Africa and southwest on the Arabic peninsula. There is an extensive literature on khat providing information about its history, botany, production, geographical distribution, chemistry and pharmacology, and exploring the social, economic, medical, psychological and oral aspects related to its use. Some of this literature dates as early as the 11th century; however, most of it appeared after the first scientific description of khat by Peter Forskal in 1775. This review provides a panorama of khat and the various aspects of its use. A non-technical description of the plant chemistry and pharmacology is included. The medical, psychological and oral aspects are emphasized, and the current knowledge about the microbiological effects of khat is also presented.

Effects of repeated-dose isradipine on the abuse liability of cocaine

Despite preclinical studies suggesting that isradipine may antagonize the abuse liability of cocaine, pretreatment with sustained-release isradipine did not reduce euphoric mood in cocaine-using volunteers. This double-blind, within-subject, crossover laboratory study determined whether maximal dose-loading with isradipine could antagonize effects of cocaine in 12 cocaine-dependent research volunteers administered intravenous cocaine doses (0, 0.325, and 0.65 mg/kg) on different days after 5 days of treatment with isradipine or placebo. Isradipine dose was 30 mg sustained release nightly plus 15 mg immediate release 2 hr before cocaine infusion. Cocaine produced dose-related increases in cocaine's subjective effects and a behavioral measure of reinforcement. Isradipine enhanced, rather than antagonized, subjective effects, indicating that isradipine does not antagonize cocaine's abuse liability in dependent research volunteers.

Topiramate prevents ecstasy consumption: a case report

The last decade has witnessed a development in the phenomenon 'ecstasy'. Several substances, with more or less the same effects, are grouped together by the term ecstasy, the best-known one being 3,4-methylenedioxymethamphetamine (MDMA). The psychopathological consequences of MDMA in humans are relatively poorly understood. In addition, the treatment approach is complicated by the lack of documented studies. Topiramate is an antiepileptic drug that has a broad spectrum of antiseizure effects, which appear to be the result of several neurostabilizing pharmacological mechanisms including facilitation of GABAergic neurotransmission and inhibition of glutametergic activity at AMPA/kainate receptors. As both GABAergic and glutametergic neurons appear to be important modulators of the brain reward system, it was postulated that topiramate would be an effective treatment for reducing MDMA consumption through the attenuation of MDMA-induced euphoria. The case of an ecstasy consumer, who started to discontinue ecstasy under topiramate treatment is presented here. Antiepileptics/mood stabilizers with glutamate inhibition activity like topiramate may present a promising new approach for challenging the consequence of drug abuse.

Early carbon monoxide intoxication: happy to be poisoned?

Carbon monoxide poisoning is the commonest cause of death by poisoning in the UK and chronic exposure is thought to be a frequently missed diagnosis. Early recognition of carbon monoxide poisoning is vital to institute prompt treatment and to prevent exposure to others. An incident of mass exposure to carbon monoxide is presented where euphoria, lasting several hours, was the only symptom reported in approximately one quarter of the casualties. This has not been reported previously and we believe that mild carbon monoxide intoxication should be included in the list of differential diagnoses of inappropriate euphoria.

Rollin' on E

Ecstasy use has spread beyond the rave and club scenes into other arenas of party culture, and from middle-class America to working-class and low-income neighborhoods of large cities. In order to explore ecstasy use among inner city adolescents and young adults, we conducted in-depth interviews with 23 poly-drug users who had used ecstasy, in Hartford, CT. Most users reported positive experiences while on the drug. Negative experiences were most often related to poly-drug mixing. However, heavy users (40+ times ever used) experienced negative aftereffects, which led them to decide to decrease or halt their use. Some participants discussed using ecstasy during sex, and irregular use of condoms. These findings point to the need for more in-depth research on MDMA use within inner city settings, with a particular focus on ethnic and cultural context, self-controlled drug use, poly-drug mixing, and sex risk behaviors.

[3,4-methylenedioxymethamphetamine ('ecstasy'): its long-term emotional and cognitive effects, and serotonin depletion]

AIMS

The main objective of this study is to describe the different neuropsychological deficits associated to the consumption of 3,4-methylenedioxymethamphetamine (MDMA or 'ecstasy'), as well as the growing evidence that attributes these deficits to the selective axonal damage to serotoninergic cells brought about by this substance.

DEVELOPMENT

MDMA is an amphetamine derivative that, like its precursor, has properties as a stimulant. Part of its chemical structure is similar to that of the hallucinogen mescaline with which it shares the capacity to alter perception. Nevertheless, the primary pharmacological effect of this substance, which is what usually leads to its use and abuse, is chiefly linked to an intense positive emotional state. This effect on the individual's mood is also usually accompanied by numerous feelings of empathy, sociability and closeness, which turn this drug into a powerful entactogenic agent (a term used in psychotherapy to describe a state of wellbeing, closeness and emotional self-awareness produced by certain compounds). The antidepressant and entactogenic effects induced by an acute dose of MDMA can be accounted for by the notable increase in serotonin bioavailability triggered by the drug. Repeated consumption of MDMA, however, ends up affecting many functions that have been related to the serotoninergic systems, such as sleep, appetite, attention and memory, or one's emotional state.

CONCLUSIONS

Most of the neuropsychological disorders found in individuals who take ecstasy on a regular basis can be explained by the selective neurodegeneration processes that the drug appears to produce in the serotonin terminals of the brain in the long run.

Effects of naloxone on respiratory sensation before and after a removal of severe respiratory stress

Severe respiratory stress causes dyspnea, and a sudden release of this stress frequently accompanies a euphoric sensation. We hypothesized that acute severe respiratory stress may result in an elaboration of endogenous opioids within the central nervous system, and that these opioids may play significant roles in relieving dyspnea and generating euphoric sensation after a sudden removal of the stress. To test this hypothesis, we examined the effects of naloxone (0.04 mg/kg, I.V.) and the placebo (normal saline) on changes in respiratory sensation before and after the release of severe respiratory stress in a double-blind, randomized, crossover study in 14 healthy adults. Acute severe respiratory stress was induced by loaded breathing with a combination of resistive loading and hypercapnia. The subjects rated their changes in sensation by using a bidirectional visual analogue scale. Naloxone pretreatment affected neither the ventilation nor the development of dyspneic sensation during loaded breathing. Naloxone pretreatment only slightly attentuated the euphoric sensation developed after the release of severe respiratory stress. These findings suggest a small role of opioids in relieving dyspnea and in generating euphoria before and after a sudden removal of stress.

Validation of retrospective reports of early experiences with smoking

Initial sensitivity to the pharmacological effects of a drug may affect patterns of future use and dependence for a wide variety of drugs. Retrospective reports of sensations experienced upon early experimentation, however, may be limited by recall bias based on time elapsed and subsequent experiences. To validate reports of early experiences with nicotine, we studied 34 smokers who had contributed retrospective data on early experiences with smoking. Half had reported experiencing a buzz from smoking their first cigarette (the "yes" group), the other half had not (the "no" group). To simulate initial sensitivity to nicotine, we asked participants to remain abstinent from smoking for 5 days to allow for the dissipation of tolerance. They then participated in a laboratory session in which they were reexposed to nicotine in an unfamiliar form (nicotine nasal spray) and asked to indicate pleasurable responses by depressing a foot pedal if and when they experienced a "pleasurable buzz." Smokers in the "yes" group were marginally more likely to be male. The two groups did not differ significantly on age or race. The "yes" group smoked significantly more cigarettes/day than the "no" group. When the two groups were compared for response to nasal spray following 5 days' abstinence, smokers in the "yes" group were marginally more likely to have signaled experiencing at least one pleasurable buzz and rated "pleasurable sensation from spray" on a 100-mm visual analogue scale administered 10 min after nicotine dosing significantly higher than were those in the "no" group. To the extent that several days' abstinence can serve as a model for initial sensitivity to nicotine, our findings validate retrospective reports of pleasurable sensations upon early smoking experimentation.

Effects of naltrexone on the subjective response to amphetamine in healthy volunteers

While dopaminergic mechanisms in amphetamine-taking behavior have been extensively studied, the contribution of the endogenous opioid system is less clear. We assessed the effects of an opioid antagonist, naltrexone (50 mg), on the subjective response to an oral dose of dexamphetamine (30 mg) in 12 healthy volunteers in a double-blind, placebo-controlled design. Volunteers received a total of 4 combinations of the study preparation (placebo-naltrexone, placebo-amphetamine) over 4 occasions with 1-week intervals. The primary objective of the study was to evaluate the effect of pretreatment with naltrexone on the subjective response to amphetamine. This was measured using a Visual Analog Scale, assessing the subjective effects over 7 hours. The secondary objective was to measure the effects of naltrexone on behavioral and physiologic responses to amphetamine. This was measured by blood pressure, heart rate, skin conductance, and speed of reading at the end of each session. Amphetamine produced significant effects on subjective arousal when compared to placebo after 1 hour (P < 0.001) and continued to be evident until 7 hours. Pretreatment with naltrexone significantly attenuated the subjective effects of amphetamine (P < 0.05), and this effect was time-dependent with a reduction from the 3-hour time point. Naltrexone did not influence the behavioral and physiologic effects of amphetamine in this sample. The results provide preliminary evidence that naltrexone may reduce the reinforcing effects of amphetamine via modulation of the opioid system. The potential of naltrexone as an adjunct pharmaceutical for the treatment of amphetamine dependence is promising and needs to be investigated further.