Reinforcing and subjective effects of diazepam in nondrug-abusing volunteers

Sleep and alertness disturbance and substance use disorders: A bi-directional relation

The majority of the literature describing the relation of sleep/alertness disturbance and substance use disorders (SUD) has focused on the disruptive effects of substances with abuse liability on sleep and alertness. Rarely have studies or literature reviews assessed or discussed how sleep/alertness disturbance affects substance use. This paper focuses on the sleep/alertness disturbance side of the relation. We argue that the relation is bi-directional and review evidence showing that sleep/alertness disturbance affects all phases of the addiction cycle, including the initiation, maintenance and relapse of SUD. We review a variety of substances across all phases of the addiction cycle and conclude sleep/alertness disturbance is a critical factor in both understanding and treating SUD.

Examining the Relationship Between Self-Reported Drinking and In-Laboratory Drinking and Craving: Is There Concordance?

BACKGROUND

In-laboratory drinking sessions that allow direct assessment of drinking and craving are an emerging method for testing novel pharmacotherapy compounds and behavioral interventions for alcohol use disorders. Despite wide implementation, limited evidence supports the concordance between drinking in the laboratory and in a natural setting. This study examined the relationship between self-reports of drinking prior to and drinking and craving during an alcohol drinking paradigm (ADP).

METHODS

Participants were adult heavy drinkers (N = 64) who participated in a pharmacotherapy study. Participants completed self-report alcohol assessments and a baseline ADP session prior to any medication administration. Alcohol craving was assessed during priming and ad lib ADP phases. Outcomes were the associations of total drinks consumed in-laboratory and summary drinking measures for the 30 days prior to the ADP and reports of maximum drinks (past year and lifetime). Additional outcomes were the association of self-reported drinking and alcohol craving during the ADP and the concordance between self-report and ADP World Health Organization (WHO) drinking classifications.

RESULTS

Number of drinking days, average drinks per drinking occasion, and lifetime and past-year maximum drinks were all related to drinking in the laboratory. Heavy drinking days were not related to drinking in the laboratory but were associated with ADP craving. Alcohol craving was also associated with other measures of self-reported drinking. There was also a significant association between WHO drinking risk classification and in-laboratory drinking.

CONCLUSIONS

The observed relationships between self-reported drinking and drinking in-laboratory across drinking indices suggest that in-laboratory alcohol consumption may reflect participants' real-world alcohol consumption, supporting the value of laboratory-based drinking paradigms. The demonstrated relationship with self-reported drinking and ADP alcohol craving further supports the value of such paradigms to model key drinking predictors. These results provide support for the validity of laboratory-based paradigms to accurately reflect participants' recent drinking levels.

Naltrexone moderates the relationship between cue-induced craving and subjective response to methamphetamine in individuals with methamphetamine use disorder

RATIONALE

Reductions in cue-induced craving and subjective response to drugs of abuse are commonly used as initial outcome measures when testing novel medications for the treatment of addiction. Yet neither the relationship between these two measures at the individual level nor the moderating effects of pharmacotherapies on this relationship has been examined.

OBJECTIVE

This secondary data analysis sought to examine (1) the predictive relationship between cue-induced craving and subsequent acute subjective response to methamphetamine (MA) and (2) whether the opioid-receptor antagonist naltrexone moderated this association in a sample of non-treatment-seeking individuals who met DSM-IV criteria for MA use disorder (abuse or dependence).

METHODS

Participants (n = 30) completed two 4-day medication regimens (oral naltrexone 50 mg or placebo, in a randomized, counterbalanced, and double-blind fashion). On day 4 of each medication regimen, participants completed a cue-reactivity paradigm followed by intravenous MA administration. Methamphetamine craving was assessed after the cue-reactivity paradigm, and subjective response to MA was assessed during MA infusion.

RESULTS

Cue-induced craving for MA was positively associated with post-infusion subjective MA effects, including positive (i.e., stimulation, good effects, feel drug, high), negative (i.e., anxious and depressed), and craving-related (i.e., want more, would like access to drug, crave) responses. Naltrexone, vs. placebo, significantly reduced the association between cue-induced craving and positive subjective response to MA.

CONCLUSIONS

The findings indicate that naltrexone moderates the predictive relationship between cue-induced craving and positive subjective effects of MA, thereby suggesting a behavioral mechanism by which naltrexone may be efficacious in treating MA use disorder.

Current insights into the mechanisms and development of treatments for heavy drinking cigarette smokers

There is a strong association between cigarette smoking and alcohol use at the epidemiological, behavioral, and molecular levels, and this co-use creates substantial impediments to smoking cessation among smokers who are also heavy drinkers. Compared with individuals who only smoke, those who both drink and smoke heavily experience more severe health consequences and have greater difficulty in quitting smoking. During smoking abstinence, greater alcohol use is associated with decreased odds of smoking cessation, and smokers are substantially more likely to experience a smoking lapse during drinking episodes. As heavy drinking smokers are less responsive to the currently available pharmacological treatments, this subgroup of high-risk substance users possesses a unique clinical profile and treatment needs. Thus, treatment development for heavy drinking smokers represents a significant and understudied research area within the field of smoking cessation. This review will briefly describe findings from epidemiological, behavioral, and molecular studies illustrating alcohol and tobacco co-use and identify how the behavioral and neurobiological mechanisms underlying the interaction of alcohol and nicotine may inform the development of targeted treatments for this unique population of smokers.

Ideal Affect: Cultural Causes and Behavioral Consequences

Most research focuses on actual affect, or the affective states that people actually feel. In this article, I demonstrate the importance and utility of studying ideal affect, or the affective states that people ideally want to feel. First, I define ideal affect and describe the cultural causes and behavioral consequences of ideal affect. To illustrate these points, I compare American and East Asian cultures, which differ in their valuation of high-arousal positive affective states (e.g., excitement, enthusiasm) and low-arousal positive affective states (e.g., calm, peace-fulness). I then introduce affect valuation theory, which integrates ideal affect with current models of affect and emotion and, in doing so, provides a new framework for understanding how cultural and temperamental factors may shape affect and behavior.

Cognitive effects of intramuscular ketamine and oral triazolam in healthy volunteers

RATIONALE

Several studies have documented impairments in memory processes as a result of ketamine administration; however, few studies have compared the profile of cognitive effects of ketamine to other drugs.

OBJECTIVES

The aim of this study was to compare the cognitive effects of ketamine with those of triazolam in healthy volunteers.

METHODS

Doses of ketamine (0.2, 0.4 mg/kg intramuscular (i.m.)), triazolam (0.2, 0.4 mg/70 kg p.o.), and double-dummy placebos were administered to 20 volunteers under repeated measures, counterbalanced, double-blind conditions. Peak physiological, psychomotor, subjective, and cognitive effects were examined.

RESULTS

Ketamine impaired balance when balance was assessed early in the task order, whereas triazolam impaired psychomotor coordination and divided attention irrespective of task order. Triazolam also tended to produce greater effects on working memory and episodic memory tasks than ketamine at doses that produced lower subjective effects and higher estimates of performance.

CONCLUSIONS

Ketamine produces less cognitive impairment than triazolam at doses that produced greater subjective effects. Thus ketamine does not produce the underestimation of cognitive impairment typically seen with triazolam.

Separate and combined psychopharmacological effects of alprazolam and oxycodone in healthy volunteers

BACKGROUND

There are epidemiological data indicating that medical and/or nonmedical use of prescription opioids oftentimes involves concurrent use of other substances. One of those substances is benzodiazepines. It would be of relevance to characterize the effects of an opioid and a benzodiazepine when taken together to determine if measures related to abuse liability-related effects and psychomotor performance impairment are increased compared to when the drugs are taken alone.

METHODS

Twenty volunteers participated in a crossover, randomized, double-blind study in which they received placebo, 0.5mg alprazolam, 10mg oxycodone, and 0.5mg alprazolam combined with 10 mg oxycodone, all p.o. Subjective, psychomotor, and physiological measures were assessed during each of the four sessions.

RESULTS

Oxycodone by itself increased drug liking and "take again" ratings relative to placebo, but these ratings were not increased when oxycodone was taken with alprazolam, which by itself did not increase either of these ratings. The two drugs in combination produced stronger effects (larger in magnitude or longer lasting) than when either was taken alone on a number of measures, including psychomotor performance impairment.

CONCLUSIONS

In healthy volunteers, abuse liability-related subjective effects of oxycodone were not enhanced by alprazolam. There was enhanced behavioral toxicity when the drugs were taken together, and thus, this is of significant concern from a public safety standpoint.

Characterizing the subjective and psychomotor effects of carisoprodol in healthy volunteers

Carisoprodol is a centrally acting drug used to relieve skeletal muscle spasms and associated pain in acute musculoskeletal conditions. There is evidence from different sources that this oral muscle relaxant is abused and that it is associated with impairment leading to arrests for "driving under the influence" as well as increased risk of automobile accidents. Its subjective and psychomotor effects in healthy volunteers at therapeutic and supratherapeutic doses have not been well-characterized, and form the basis of this report. Fifteen healthy volunteers (8 males, 7 females) were administered 0, 350, and 700 mg of carisoprodol in separate sessions and for 6h afterwards they completed a battery of tests at fixed time intervals so as to assess the subjective and psychomotor effects of the drug. The supratherapeutic dose, 700 mg, increased visual analog scale ratings of terms that were more reflective of sedation (e.g., "sleepy," "heavy, sluggish feeling") than those of abuse liability, and produced impaired performance on several psychomotor tests. The therapeutic dose, 350 mg, while producing few and mild subjective effects, still produced psychomotor impairment. The fact that the therapeutic dose of carisoprodol produced minimal subjective effects while adversely affecting performance is of concern in that patients prescribed this drug may feel relatively normal and engage in tasks (driving) that could put themselves and others at risk.

Amphetamine self-administration in light and moderate drinkers

BACKGROUND

Light and moderate drinkers respond differently to the effects of abused drugs, including stimulants such as amphetamine. The purpose of this study was to determine whether light and moderate drinkers differ in their sensitivity to the reinforcing and subjective effects of d-amphetamine. We hypothesized that moderate drinkers (i.e., participants that reported consuming at least seven alcohol-containing beverages per week) would be more sensitive to the reinforcing and positive subject-rated effects of d-amphetamine than light drinkers.

METHODS

Data from four studies that employed similar d-amphetamine self-administration procedures and subject-rated drug-effect measures were included in the analysis. Light (n = 17) and moderate (n = 16) drinkers sampled placebo, low (8 to 10 mg), and high (16 to 20 mg) doses of oral d-amphetamine administered in eight capsules. Following sampling sessions, participants worked for a maximum of eight capsules, each containing 12.5% of the previously sampled dose, on a modified progressive-ratio schedule of reinforcement.

RESULTS

Both active doses of d-amphetamine functioned as a reinforcer in the moderate drinkers, while only the high dose did so in the light drinkers. The moderate drinkers worked for significantly more capsules that contained the high dose of d-amphetamine than did the light drinkers. d-Amphetamine produced prototypical stimulant-like subjective effects (e.g., dose-dependent increases in ratings of Good Effects; Like Drug and Willing to Take Again). Moderate drinkers reported significantly greater subjective effects than the light drinkers.

CONCLUSION

These results are consistent with those from previous laboratory experiments and suggest that moderate alcohol consumption may increase vulnerability to the abuse-related effects of stimulants.

Psychopharmacological effects of oxycodone in healthy volunteers: roles of alcohol-drinking status and sex

BACKGROUND

Studies have shown that alcohol-drinking status modulates psychopharmacological effects of several drugs. We sought to determine if drinking status modulates the effects of a prescription opioid, oxycodone, in healthy volunteers. We included sex of the volunteer in the statistical analyses since this is a factor that is known to alter several pharmacodynamic effects of opioids in nonhumans and humans.

METHODS

Fifteen light drinkers (eight males) and 14 moderate drinkers (eight males) participated in a crossover, randomized, double-blind study in which they received 0, 10, and 20mg of oxycodone (p.o.). Dependent measures were subjective, psychomotor/cognitive, reinforcing, and physiological effects.

RESULTS

Self-reported alcohol-drinking status did not modulate the effects of oxycodone. However, there were a number of Sex x Dose interactions with females reporting more and larger unpleasant effects than males (e.g., visual analog scale ratings of "nauseated" greater in females than in males).

CONCLUSIONS

Studies have established that moderate drinkers report a greater degree of abuse liability-related effects than do light drinkers with several different drugs, including diazepam, amphetamine, and nitrous oxide, but we were unable to establish this with the prescription opioid, oxycodone. However, we did observe sex differences in several subjective effects of oxycodone, a finding that is consistent with the extant literature showing sex differences in pharmacodynamic effects of opioids.

Are attention lapses related to d-amphetamine liking?

RATIONALE

A rich literature suggests that both impulsiveness and drug-induced euphoria are risk factors for drug abuse. However, few studies have examined whether sensitivity to the euphoric effects of stimulants is related to attention lapses, a behavioral measure of inattention sometimes associated with impulsivity.

OBJECTIVE

The aim of the study was to examine ratings of d-amphetamine drug liking among individuals with high, moderate, and low attention lapses.

METHODS

Ninety-nine healthy volunteers were divided into three equal-sized groups based on their performance on a measure of lapses of attention. The groups, who exhibited low, medium, and high attention lapses (i.e., long reaction times) on a simple reaction time task, were compared on their subjective responses (i.e., ratings of liking and wanting more drug) after acute doses of d-amphetamine (0, 5, 10, and 20 mg).

RESULTS

Subjects who exhibited high lapses liked 20 mg d-amphetamine less than subjects who exhibited low lapses. These subjects also tended to report smaller increases in "wanting more drug" after d-amphetamine.

CONCLUSION

The findings suggest that participants who exhibit impaired attention may be less sensitive to stimulant-induced euphoria.

Within-subject comparison of the psychopharmacological profiles of oral hydrocodone and oxycodone combination products in non-drug-abusing volunteers

BACKGROUND

Non-medical use and abuse of prescription opioids is a significant problem in the United States. Little attention has been paid to assessing the relative psychopharmacological profile (including abuse liability-related effects) of specific prescription opioids. The purpose of this study was to directly compare the psychopharmacological profile of two widely prescribed and abused oral opioid combination products within the same subject.

METHODS

Twenty non-drug-abusing volunteers participated in a crossover, randomized, double-blind study in which they received, all p.o.: placebo; 975 mg acetaminophen (ACET); 10mg oxycodone (OXY)/487 mg ACET; 20mg OXY/975 mg ACET; 15 mg hydrocodone (HYD)/487 mg ACET; and 30mg HYD/975 mg ACET. OXY and HYD doses were chosen to equate the drugs on an objective measure of opiate effects: miosis. Dependent measures were subjective, psychomotor/cognitive, reinforcing, and physiological effects, and relative potency estimates.

RESULTS

In general, the two opioid combination products at equi-miotic doses produced similar prototypic opiate-like effects and psychomotor impairment, and of similar magnitude. The higher dose of OXY/ACET produced slightly more abuse liability-related subjective effects than the higher dose of HYD/OXY, but also produced slightly more negative effects. Neither drug at either dose functioned as a reinforcer, as measured by the Multiple Choice Procedure. Relative potency ratios indicated that OXY/ACET was approximately 1.5 times more potent than HYD/ACET.

CONCLUSIONS

Consistent with a recent study published in this journal using identical doses of HYD and OXY (without ACET) in prescription opioid abusers (Walsh, S.L., Nuzzo, P.A., Lofwall, M.R., Holtman Jr., J.R., 2008. The relative abuse liability of oral oxycodone, hydrocodone and hydromorphone assessed in prescription drug abusers. Drug Alcohol Depend. 198, 191-202), we found little difference in the pharmacodynamic effects of HYD/ACET and OXY/ACET in non-drug-abusing volunteers.

Choice of nitrous oxide and its subjective effects in light and moderate drinkers

BACKGROUND

Alcohol-drinking status has been shown to modulate the reinforcing and subjective effects of a number of drugs. We have previously published two studies on the modulating effects of alcohol-drinking status on choice for, and subjective effects of, nitrous oxide, but the results were equivocal. Using a methodology different from our previous studies, we sought to determine in a more definitive fashion the degree to which the choice of nitrous oxide and its subjective effects were modulated by drinking status.

METHODS

Four concentrations of nitrous oxide (0, 20, 30, and 40%) were administered to 16 moderate drinkers (MDs) and 16 light drinkers (LDs) across four 3.5-h sessions. During experimental sessions, subjects first completed two 10-min sampling trials in which one of the nitrous oxide concentrations and placebo (100% oxygen) were inhaled. Subjective and psychomotor tests were given 5min into each sampling trial. During the subsequent choice period, subjects were allowed to choose what they wanted to inhale (drug, placebo, or "drug-free air") on nine contiguous 5-min choice trials.

RESULTS

Choice of nitrous oxide was modulated by drinking status: MDs but not LDs chose nitrous oxide significantly more times than placebo, and MDs also chose nitrous oxide significantly more times than did LDs. At each active nitrous oxide concentration, MDs reported more abuse liability-related subjective effects, especially at the 20% and 30% concentrations.

CONCLUSIONS

The results of the present study provide more conclusive evidence that choice as well as subjective effects of nitrous oxide is modulated by alcohol-drinking status.

Choice of sevoflurane and its subjective and psychomotor effects in light and moderate drinkers

BACKGROUND

Sevoflurane, an inhalant of the volatile anesthetic class, has neurobiological and behavioral effects in common with abused inhalants and ethanol. We sought to determine if choice for subanesthetic doses of sevoflurane, and its subjective and psychomotor effects, would differ as a function of alcohol-drinking status in healthy volunteers.

METHODS

The effects of four concentrations of sevoflurane (0, 0.2, 0.4, 0.8% sevoflurane in oxygen) were studied in 16 light drinkers and 16 moderate drinkers. During each of four sessions, subjects sampled a concentration of sevoflurane and 100% O(2) (placebo) for 10 min each. Subjective and psychomotor testing commenced 5 min into each sampling trial. Later, within the session, subjects chose nine times, once every 5 min, among sevoflurane (e.g., "Agent A"), placebo (e.g., "Agent B," 100% O(2)), or neither (and were administered 100% O(2), identified as "drug-free air").

RESULTS

Choice for sevoflurane at the 0.4% concentration was significantly higher in the moderate drinkers than in the light drinkers. A number of subjective effects reported during inhalation of sevoflurane were markedly lower in the moderate-drinking group than in the light-drinking group. However, psychomotor impairment induced by sevoflurane was similar in magnitude in both groups.

CONCLUSIONS

Alcohol-drinking status affected sevoflurane choice. The results are consistent with several studies comparing light and heavier drinkers, using other drugs. Although both drinking groups were similarly impaired by sevoflurane, the moderate drinkers reported less of a subjective response than light drinkers, suggestive of cross-tolerance.

Predictors of long-term benzodiazepine abstinence in participants of a randomized controlled benzodiazepine withdrawal program

OBJECTIVE

To identify predictors of resumed benzodiazepine use after participation in a benzodiazepine discontinuation trial.

METHOD

We performed multiple Cox regression analyses to predict the long-term outcome of a 3-condition, randomized, controlled benzodiazepine discontinuation trial in general practice.

RESULTS

Of 180 patients, we completed follow-up for 170 (94%). Of these, 50 (29%) achieved long-term success, defined as no use of benzodiazepines during follow-up. Independent predictors of success were as follows: offering a taper-off program with group therapy (hazard ratio [HR] 2.4; 95% confidence interval [CI], 1.5 to 3.9) or without group therapy (HR 2.9; 95% CI, 1.8 to 4.8); a lower daily benzodiazepine dosage at the start of tapering off (HR 1.5; 95% CI, 1.2 to 1.9); a substantial dosage reduction by patients themselves just before the start of tapering off (HR 2.1; 95% CI, 1.4 to 3.3); less severe benzodiazepine dependence, as measured by the Benzodiazepine Dependence Self-Report Questionnaire Lack of Compliance subscale (HR 2.4; 95%CI, 1.1 to 5.2); and no use of alcohol (HR 1.7; 95% CI, 1.2 to 2.5). Patients who used over 10 mg of diazepam equivalent, who had a score of 3 or more on the Lack of Compliance subscale, or who drank more than 2 units of alcohol daily failed to achieve long-term abstinence.

CONCLUSIONS

Benzodiazepine dependence severity affects long-term taper outcome independent of treatment modality, benzodiazepine dosage, psychopathology, and personality characteristics. An identifiable subgroup needs referral to specialized care.

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.

Critical assessment of how to study addiction and its treatment: human and non-human animal models

Laboratory models, both animal and human, have made enormous contributions to our understanding of addiction. For addictive disorders, animal models have the great advantage of possessing both face validity and a significant degree of predictive validity, already demonstrated. Another important advantage to this field is the ability of reciprocal interplay between preclinical and clinical experiments. These models have made important contributions to the development of medications to treat addictive disorders and will likely result in even more advances in the future. Human laboratory models have gone beyond data obtained from patient histories and enabled investigators to make direct observations of human drug self-administration and test the effects of putative medications on this behavior. This review examines in detail some animal and human models that have led not only to important theories of addiction mechanisms but also to medications shown to be effective in the clinic.

Reinforcing effects of diazepam under anxiogenic conditions in individuals with social anxiety

Diazepam (DZ) reinforcement was tested under anxiogenic (public speaking) and neutral (computer task) conditions. Individuals with social anxiety disorder (n = 11) and healthy controls (n = 11) participated in two 5-session phases. Each phase used a standard choice procedure (2 sample, 3 choice sessions) comparing 10-mg DZ and placebo. During the public speaking condition, DZ preference was greater among the participants with social anxiety compared with controls (81.8% vs. 36.4%; p < .05). Participants with social anxiety also gave DZ significantly higher crossover values on the multiple choice procedure under the speech condition compared with the computer condition. Subjective effects indicated that DZ reduced anxiety when levels were elevated during the speech in socially anxious participants. These results suggest that DZ reinforcement may occur under conditions of heightened anxiety by bestowing therapeutic efficacy.

Reinforcing and subjective effects of the volatile anesthetic, sevoflurane

Sevoflurane is a volatile anesthetic that is chemically similar to volatile substances of abuse and can be safely administered to humans in laboratory research. In this study, the reinforcing and subjective effects of five concentrations of sevoflurane (0, 0.2, 0.4, 0.6, 0.8% sevoflurane in O2) were studied in 20 non-drug-abusers. During each of five sessions, subjects sampled a concentration of sevoflurane and 100% O2 (placebo) for 10 min each. Later, within the session, they chose nine times, once every 5 min, among sevoflurane (e.g. "Agent A"), placebo (e.g. "Agent B"), or neither (and were administered 100% O2, identified as "drug-free air"). Although "neither" was selected most frequently, mean preference ratios (sevoflurane choices/[sevoflurane choices+placebo choices]) and total sevoflurane choice peaked at the 0.4% concentration. Choice patterns varied across subjects, with some subjects never choosing sevoflurane and other subjects showing monotonic increasing or bitonic concentration-choice functions. Concentration-related increases in subjective effects were observed, including effects that are putatively associated with abuse liability. Ratings of drug liking and of wanting to inhale the drug again were positively correlated with sevoflurane choice. This study shows that sevoflurane can function as a reinforcer and produce abuse liability-related subjective effects in some healthy volunteers.

Principles of initial experimental drug abuse liability assessment in humans

This paper describes the rationale and procedures for conducting what is considered by many to be the current "gold standard" for initial abuse liability testing of a novel compound: the classic acute dose-effect comparison study in volunteers with histories of drug abuse. Such a trial is most appropriate for predicting the likelihood of abuse by drug abusers and, in turn, the extent of drug diversion and illicit street sales if the novel compound became available in the community. The dose-effect abuse liability trial typically involves a double-blind complete crossover design in 10-14 subjects with histories of polydrug abuse in a controlled clinical pharmacology laboratory setting. Drug conditions usually involve placebo, three doses of the novel compound and three doses of an appropriate reference compound of known abuse liability. In each session, the time-course of effects of a single drug dose are evaluated. Intervals between experimental sessions are typically 1 to several days. The importance of testing high supra-therapeutic doses of the novel drug for the validity of the trial is emphasized, and the use of a dose run-up pilot study for selecting maximal doses and matching doses between the novel and comparison compound is explained. The rationale and description of outcome measures is discussed, including measures that reflect likelihood of abuse (e.g. drug vs. money choice and subject ratings of liking, good effects, estimated monetary street value), secondary measures that should be considered in interpreting likelihood of abuse (e.g. drug identification, subject-rated side effects and mood changes), and additional concurrent measures to establish equivalence of the novel and comparison compound (e.g. behavioral performance, observer-rated assessments, physiological measures).

The effects of alprazolam and buspirone in light and moderate female social drinkers

Individuals who are moderate/heavy drinkers are at increased risk to abuse benzodiazepines and this risk is increased in women compared to men. However, no studies have determined whether female moderate drinkers (MD) show a differential response to the subjective and performance effects of benzodiazepines compared to female light drinkers (LD). Fourteen female MD who consumed an average of 36 drinks/month were compared to 14 female LD who consumed an average of 4.2 drinks/month. None of the participants had either a first- or second-degree family history of alcoholism. The acute effects of placebo, alprazolam (0.25, 0.50, 0.75 mg) and buspirone (5, 10, 15 mg) were evaluated using a double-blind, placebo-controlled outpatient design. Drug effects were assessed using a full range of performance measures and subjective-effects questionnaires. Alprazolam impaired performance in a dose-related manner on all performance tasks for both groups of females, whereas buspirone had minimal effects on performance. There were few differences between LD and MD with respect to subjective response or performance impairment following either alprazolam or buspirone. Although MD reported greater ratings of Good Drug Effect and Drug Liking than LD, this was neither dose-related, nor specific to alprazolam. The results of the present study suggest that female MD without a family history of alcoholism experience the same level of performance impairment as female LD, although they tend to report greater positive subjective effects from alprazolam.

Within- and between-subject variability in the reinforcing and subjective effects of nitrous oxide in healthy volunteers

Within- and between-subject variability in the reinforcing and subjective effects of nitrous oxide (N(2)O) was studied across five sessions. Twelve volunteers with no history of drug dependence sampled 30% N(2)O and 100% oxygen for 10 min each, then chose nine times, once every 5 min, among N(2)O (e.g. "Agent A"), oxygen (e.g. "Agent B"), or "drug-free air." Choice varied across subjects but was stable within subjects. Quantitative differences in subjective effects occurred within and across subjects. Some subjective effects were correlated with choice and/or differed between subjects who were consistent choosers of N(2)O versus those who were not. However, drug liking and euphoria, two face-valid measures of abuse liability, were unrelated to choice. Thus, the present study found individual differences (i.e. between-subject variability) in subjective and reinforcing effects of N(2)O and, in terms of within-subject variability, suggested that subjective effects fluctuate across sessions to a relatively greater extent than do reinforcing effects. The varying degrees of correlation between N(2)O choice and its subjective effects emphasize the need for obtaining multiple measures when characterizing abuse liability of this drug.

Investigation of preference for nightly triazolam versus placebo in moderate social alcohol drinkers

This study was designed to examine whether the widely prescribed benzodiazepine hypnotic triazolam has reinforcing effects in moderate social alcohol drinkers, without histories of drug abuse or insomnia, in the context of its use as a hypnotic. Eleven healthy adult volunteers who met criteria for 'good sleepers' participated in a 60-session double-blind choice study which was conducted on an outpatient basis with participants sleeping at home. Twenty three-session sampling/choice tests were conducted sequentially to provide 20 evaluations of the reinforcing effects of 0.25 mg/70 kg triazolam versus placebo, ingested orally 30 min before bedtime. Each three-session test consisted of two sampling sessions, in which participants received exposure to each of the two drug conditions in different colored capsules, followed by one choice session, in which participants were asked to choose one of the two colour-coded capsules for self-administration. Four participants exhibited a significant choice of triazolam, three, a significant choice of placebo (i.e. triazolam avoidance), and four, a random (i.e. non-significant) choice between triazolam and placebo. The reasons provided by participants were consistent with their choices and with the expected effects of triazolam versus placebo. Analyses of post-sleep questionnaires indicated that triazolam did not produce a clinically meaningful improvement in sleep. The finding that triazolam functioned as a reinforcer in participants without insomnia suggests that triazolam has reinforcing effects in some individuals for which hypnotic treatment is not clinically indicated, and that health care professionals must continue to assess the risk/benefit ratio of benzodiazepine hypnotic prescription.

Abuse liability of flunitrazepam

Flunitrazepam is among the most frequently prescribed hypnotics in many countries. Although it was never marketed in the United States, flunitrazepam, in recent years, has been smuggled into the country, and reports of abuse--including alleged use of the drug to facilitate "date rape"--have attracted a great deal of scrutiny. It has been suggested that flunitrazepam may have greater liability for abuse than other benzodiazepines; such suggestions are supported by surveys of opioid abusers, many of whom report a distinct preference for flunitrazepam over other benzodiazepines. Experimental studies of animals and normal human subjects indicate that, although flunitrazepam has high efficacy and is very potent, it is pharmacologically similar to most other benzodiazepines. Although the studies are limited in number and scope, the data show no apparent differences between flunitrazepam and other benzodiazepines in ability to produce drug-taking or drug-seeking behavior, in capacity to produce physiologic dependence, nor in the characteristics of withdrawal after administration of an antagonist or discontinuation of treatment. Similar to other benzodiazepines, flunitrazepam produces dose-dependent effects on psychomotor performance and recall. Flunitrazepam does not seem to be involved in medical emergencies more often than other benzodiazepines, and there is no indication that flunitrazepam is more toxic than other benzodiazepines when taken in overdose by drug abusers or other individuals. Survey research among typical patient populations suggests that flunitrazepam is characteristic of benzodiazepines in that it is used appropriately and conservatively, with low liability for abuse. Thus the reported preference for flunitrazepam among opioid abusers seems to be the only way in which flunitrazepam is distinguished from other benzodiazepines; it is unclear what characteristics of the drug may be responsible for this reported preference. The evidence considered in this review indicates that abuse of flunitrazepam in this special population is not associated with any distinctive threats to the health of the general public.

Alprazolam-reinforced medication use in outpatients with anxiety

The reinforcing effects of alprazolam were investigated in 14 patients who had generalized anxiety or panic disorder, but were not current users/abusers of other psychoactive substances. Using a double-blind outpatient choice procedure, color-coded alprazolam (0.5 mg) and placebo capsules were provided to patients for use 'as needed' in the treatment of anxiety symptoms. Comparisons of alprazolam and placebo during a 2 week sampling period in which placebo and alprazolam were available sequentially revealed no significant differences on measures of medication usage or anxiety levels, although alprazolam did increase subjective ratings of drug effects side effects. During a 4 week choice period, alprazolam was strongly preferred over placebo in 11 out of 14 patients indicating that alprazolam functioned as a reinforcer. Medication usage ranged from zero to 4.0 mg alprazolam in a day. Variations in daily medication-use were positively correlated with anxiety level fluctuations for a majority of patients. For a majority of patients, the results indicate that alprazolam functioned as a reinforcer without accompanying signs of abuse or addiction.

The effects of alcohol history on the reinforcing, subjective and psychomotor effects of nitrous oxide in healthy volunteers

The purpose of this study was to characterize the reinforcing, subjective and psychomotor effects of nitrous oxide in healthy volunteers with different alcohol histories. Subjects were divided into two groups: light drinkers (n = 9) and moderate drinkers (n = 10). A choice procedure was used in which subjects first sampled placebo and a given concentration of nitrous oxide, and then chose between the two. Nitrous oxide concentration varied across the four-session experiment from 10-40%. Besides choice, subjective and psychomotor effects served as dependent measures. The majority of subjective effects of nitrous oxide, and its psychomotor-impairing effects, did not vary as a function of drinking group. However, a Wilcoxon rank sum test showed that the median number of times moderate drinkers chose nitrous oxide (three) was significantly higher than the median number of times light drinkers chose nitrous oxide (one). This study provides suggestive evidence that the reinforcing effects of nitrous oxide are modulated by alcohol history.

The reinforcing effects of brief exposures to nitrous oxide in healthy volunteers

The reinforcing and subjective effects of brief (about 1.5 min) exposures to nitrous oxide, ranging from inspired concentrations of 20-80% in oxygen, were examined in 11 healthy volunteers. A choice procedure was used in which during each of four sessions, subjects first sampled a given concentration of nitrous oxide and placebo oxygen, and then chose between the two. 20, 40, 60 and 80% nitrous oxide were chosen by five, four, three, and three subjects, respectively--these choice levels did not exceed that of chance. All concentrations had psychoactive effects, and in general, concentration-related subjective effects were found. We conclude that in a medical setting, nitrous oxide inhaled in a manner similar to that when used recreationally in a naturalistic setting, does not function as a reinforcer across a wide range of concentrations, in subjects with a modest lifetime history of psychoactive drug use.

Influence of training dose on nicotine discrimination in humans

Non-human research indicates that drug discrimination results may depend largely on the specific training conditions, including initial training dose. It has recently been shown that humans can discriminate among different doses of nicotine delivered by nasal spray. In this study, we examined the influence of training dose on subsequent behavioral discrimination of a range of nicotine doses. Male (n = 17) and female smokers (n = 16) were randomly assigned to "low" (10 micrograms/kg) versus "high" (30 micrograms/kg) nicotine training dose groups and trained reliably to discriminate this dose from placebo (0) on day 1 (> or = 80% correct identification). All but six subjects (four in low, two in high) learned this discrimination and continued on to day 2, in which both groups received 0, 5, 10, 20, and 30 micrograms/kg in ascending order (30 min between dosings) and were tested for generalization with their training dose using quantal and quantitative behavioral discrimination tasks. Subjective responses via traditional self-report measures were also assessed. Nicotine-appropriate responding on day 2 was significantly greater in low- versus high-dose groups, especially at 5 micrograms/kg. However, this difference due to training dose was seen more in women than in men. Discrimination behavior was associated with subjective effects of head rush in males, and with head rush and decline in urge to smoke in females. These results show that discriminative stimulus effects of nicotine are not fixed properties of the drug, but can be influenced by training conditions, and that effects associated with this discrimination may differ between men and women.

Zolpidem, triazolam, and temazepam: behavioral and subject-rated effects in normal volunteers

Zolpidem is an imidazopyridine hypnotic that is biochemically distinct from classic benzodiazepine agonists in that it may be selective for the BZ1 receptor subtype and shows a different pattern of distribution of binding sites. The present study compared the learning, recall, performance, subject-rated and observer-rated effects of zolpidem, triazolam, and temazepam in 11 healthy humans. Placebo, zolpidem (5, 10, and 20 mg/70 kg), triazolam (0.125, 0.25, and 0.50 mg/70 kg), and temazepam (15, 30, and 60 mg/70 kg) were administered orally in a randomized, double-blind, cross-over design. Zolpidem, triazolam, and temazepam produced orderly dose- and time-related impairment of learning, recall, and performance, and increased subject- and observer-rated estimates of strength of drug effect. The absolute magnitude of these effects at peak effect were comparable across the three compounds. The time to maximal drug effect was faster with zolpidem (0.5-1.0 hours) than with triazolam (1.5-2.0 hours) or temazepam (2-3 hours). These results suggest that despite the somewhat unique benzodiazepine receptor-binding profile of zolpidem, its behavioral and subject-rated effects are similar to those of benzodiazepine hypnotics (i.e., triazolam and temazepam).

Preference for diazepam, but not buspirone, in moderate drinkers

The purpose of the present study was to determine the preference for buspirone, an anxiolytic predicted to have minimal abuse potential, in comparison with diazepam in moderate drinkers. Preference for diazepam and buspirone was assessed in 55 moderate drinkers using a seven-session procedure consisting of four sampling sessions followed by three choice sessions. On each sampling session subjects ingested five capsules, one every 30 min. Color-coded capsules contained placebo on two sessions and drug on two sessions. Each drug capsule contained diazepam (4 mg) for 30 subjects and buspirone (5 mg) for 25 subjects. On choice sessions subjects chose whichever of the two color-coded capsules, i.e., drug or placebo, they wished to take. After ingesting one capsule, every 30 min they had the option of ingesting another capsule of the same color and content, for a maximum of seven capsules over the session (maximum of 28 mg diazepam or 35 mg buspirone). In the diazepam group 70% of subjects chose diazepam over placebo on at least two of the three choice sessions, whereas in the buspirone group only 24% of subjects chose buspirone over placebo on at least two sessions. Both diazepam and buspirone increased measures of sedation. Only diazepam increased ratings of liking and impaired performance, whereas only buspirone decreased ratings of feeling Friendly. These results replicate previous findings indicating that diazepam has reinforcing effects in moderate drinkers. Further, these results demonstrate the pharmacological specificity of this effect by showing that buspirone did not function as a reinforcer under these same conditions.

Effects of several benzodiazepines, alone and in combination with flumazenil, in rhesus monkeys trained to discriminate pentobarbital from saline

The purpose of the present study was to further investigate the relationship between the DS effects of PB and those of benzodiazepines (BZs) and to begin to collect pharmacological information concerning receptor mechanisms involved in this behavioral effect of BZs. Rhesus monkeys (n = 3), trained to discriminate pentobarbital (PB; 10 mg/kg, IG) from saline under a discrete-trials shock avoidance procedure, were given IG diazepam (0.3-10 mg/kg), chlordiazepoxide (1.0-30 mg/kg), or etizolam (0.3-10 mg/kg) alone and in combination with flumazenil (0.01-1.7 mg/kg, IM). Flumazenil was administered 10 min prior to the administration of saline, PB or the BZs. All three BZs fully substituted for PB in all monkeys. Diazepam was the most potent with a mean ED50 of 0.81 mg/kg (SEM = 0.04) while chlordiazepoxide was the least potent (mean ED50 = 5.78 mg/kg, SEM = 1.22 mg/kg). The ED50 for etizolam was 1.22 mg/kg (SEM = 0.37 mg/kg). Pretreatment with flumazenil (0.01-1.0 mg/kg) resulted in a dose-related parallel shift to the right in the dose-response function for PB-appropriate responding in all monkeys for all three BZs. The mean (n = 3) pKB value with 0.1 mg/kg flumazenil was 6.51 (SEM = 0.42) for diazepam and 6.57 (SEM = 0.17) for chlordiazepoxide. This value could not be calculated for etizolam because only one monkey was tested with 0.1 mg/kg flumazenil. However, the mean pKB for etizolam considering all monkeys and all doses of flumazenil was 6.58 (SEM = 0.47). Apparent pA2 values for flumazenil with diazepam were 6.02 for one monkey and 7.11 for another. All three BZs tended to increase average latency to respond. Apparent pKB and pA2 analysis may prove useful for elucidating receptor mechanisms involved in the behavioral effects of BZs.

Preferences for ethanol and diazepam in anxious individuals: an evaluation of the self-medication hypothesis

The self-medication hypothesis of addictive disorders postulates that individuals with psychiatric symptoms use drugs to alleviate their symptoms. Although commonly cited to explain the etiology of substance abuse, self-medication has not been experimentally validated. This study evaluated one version of the self-medication hypothesis by formulating it into a testable hypothesis: are highly anxious volunteers more likely to self-administer anxiolytic drugs than non-anxious controls. Anxious (ANX, n = 22) and control (CTL, n = 23) subjects participated in two double-blind placebo-controlled experiments, one testing ethanol (0.8 g/kg) and the other testing diazepam (20 mg). Subjects sampled and then chose between ethanol and placebo in one experiment, and diazepam and placebo in the other. The main dependent measures were choice of drug over placebo and subjective responses to the drugs. Ethanol decreased self-reported anxiety in ANX subjects, but ANX subjects did not choose ethanol more often than CTL subjects. Diazepam did not measurably reduce anxiety, but ANX subjects nevertheless chose diazepam more often than did CTL subjects. Thus, there were some differences in drug responses between the ANX and CTL subjects, and the study provided limited support for the self-medication hypothesis. However, drug choice was not directly related to anxiolytic drug effects with either ethanol or diazepam. The procedure may be used to test other formulations of the self-medication hypothesis (e.g., examining other psychiatric risk factors).

Acute tolerance to nicotine in smokers: lack of dissipation within 2 hours

Greater understanding of development and dissipation of acute tolerance to nicotine may help explain temporal patterns of nicotine self-administration in smokers. The time course of dissipation of acute tolerance to nicotine was examined in 16 smokers (8M, 8F) participating in four sessions differing on pretreatment exposure or time interval prior to nicotine (20 micrograms/kg) challenge: placebo 30 min before, or nicotine (20 micrograms/kg) 30, 60, or 120 min before challenge. Nicotine and placebo were administered by measured-dose nasal spray. The measurement battery consisted of subjective, cardiovascular, thermal pain detection, and behavioral performance measures. Results demonstrated significant acute tolerance (i.e. smaller responses to nicotine challenge following nicotine versus placebo pretreatment) for most subjective measures and for heart rate. Acute tolerance dissipated with lengthening inter-dose interval for two subjective measures, dose strength and arousal, but there was no tolerance dissipation for other measures. In contrast, nicotine pretreatment resulted in acute sensitization of finger temperature (vasoconstriction) response, which dissipated with lengthening interval. No acute tolerance was observed for thermal pain detection or performance measures. These findings demonstrate that acute tolerance develops quickly to some subjective and cardiovascular effects of nicotine. However, acute tolerance to most effects did not dissipate over 2 h, suggesting that, following acute tolerance development during initial exposure, most smokers generally obtain similar magnitude of effects from each subsequent nicotine exposure (i.e. cigarettes smoked later in the day).

Current benzodiazepine issues

This article deals with some of the recent evidence bearing on the issues of the liability of benzodiazepines to lead to abuse, dependence, and adverse behavioral effects. Reviews of epidemiological, clinical and experimental literature indicated that the previous conclusion about abuse of these drugs still holds: the vast majority of the use of benzodiazepines is appropriate. Problems of nonmedical use arise nearly exclusively among people who abuse other drugs. Nevertheless, there are reasons for concern about patients who take benzodiazepines regularly for long periods of time. These drugs can produce physiological dependence when taken chronically, and although this does not appear to result in dose escalation or other evidence of "psychological dependence," physiological dependence can result in patient discomfort if drug use is abruptly discontinued. Also, physicians are currently prescribing shorter-acting benzodiazepines in preference to longer-acting benzodiazepines. The shorter-acting drugs can produce a more intense withdrawal syndrome following chronic administration. Furthermore, rates of use of benzodiazepines increase with age, and elderly patients are more likely than younger ones to take the drug chronically. The clearest adverse effect of benzodiazepines is impairment of memory. This, too, may be particular concern in older patients whose recall in the absence of drug is typically impaired relative to younger individuals, and who are more compromised following drug administration.

Personality and drug preferences in normal volunteers

This study examined the relationship between drug preferences as measured in a laboratory-based choice procedure and measures of personality and attitudes toward drugs. Healthy volunteers participated in laboratory-based double-blind studies measuring preference for ethanol or diazepam vs placebo. Frequency of drug choice was examined in relation to subjects' scores on personality questionnaires. Drug choice was not related to any of the personality measures examined. Personality scores were, however, related to both gender and habitual drug use. These data suggest that personality does not strongly influence responses to single doses of drugs as assessed under controlled conditions. Personality may, nevertheless, affect drug use in natural settings via other mechanisms (e.g., interacting with psychosocial variables).

Preference for ethanol and diazepam in light and moderate social drinkers: a within-subjects study

Preference for ethanol (versus placebo) and diazepam (versus placebo) was assessed in light and moderate social drinkers. The study was designed to investigate the relationship of habitual alcohol use to the subjective and behavioral effects of the two drugs. A secondary purpose of the study was to investigate relationships within subjects in their responses to ethanol and diazepam. Light drinkers (n = 13) who consumed one to five drinks per week and moderate drinkers (n = 14) who consumed seven or more drinks per week participated in two seven-session choice experiments, one assessing preference for 0.5 g/kg ethanol versus placebo and the other assessing preference for 20 mg diazepam versus placebo. Drugs were administered double-blind and double-dummy, and the order of participation in the two experiments was counterbalanced. Sessions were conducted during the evenings in a comfortable laboratory environment. The primary dependent measure was the number of times each subject chose the drug (i.e., ethanol or diazepam) over placebo. Subjective and objective measures of the drugs' effects were obtained using standardized self-report questionnaires and psychomotor tests. Whereas both groups preferred the ethanol over placebo (i.e., 63% and 83% ethanol choice for light and moderate drinkers, respectively), only the moderate drinkers preferred the diazepam over placebo (i.e., 40% and 73% diazepam choice for light and moderate drinkers, respectively). Subjective responses to the drugs were generally similar across the groups, although on some measures the light drinkers reported more marked drug effects. The number of times each subject chose ethanol was positively correlated with the number of times he or she chose diazepam (r = 0.57), and on subjective measures, responses to ethanol and diazepam were positively correlated. Thus, subjective and behavioral responses to diazepam and ethanol were related to habitual alcohol consumption, and most notably, moderate drinkers were more likely than light drinkers to prefer diazepam over a placebo.

Systemic absorption and abuse liability of snorted flunitrazepam

Benzodiazepine hypnotics are widely abused as part of a polydrug misuse culture. This study set out to investigate some pharmacokinetic and pharmacodynamic characteristics of a novel method of abuse, snorting, of flunitrazepam. Twenty healthy volunteers took part: three took 0.5 mg, three took 1 mg, three took 1.5 mg, six took 2 mg and five took placebo. Blood was sampled and ratings of mood, bodily symptoms, strength and liking of drug effect were completed pre- and at 5, 15, 30, 60, 90, 120 and 240 minutes and at 24 hours post-drug. It was found that flunitrazepam could be detected in venous blood 5 minutes after intake. As the dose increased, the peak plasma concentration was higher but also occurred progressively later, the levels reached being comparable to oral or intramuscular administration at 110 minutes. Subjects reported sedation but complained of few side-effects. They liked the drug effects and subjective ratings of strength were correlated with liking and with plasma drug levels.

Relationship between subjective effects and drug preferences: ethanol and diazepam

The relationship between subjective effects and drug preferences in normal volunteers was explored in a meta-analysis of several previously published studies. Subjective effects of, and preference for, ethanol and diazepam vs. placebo were measured using a choice procedure. Subjects were grouped according to their drug choices: 'non-choosers' never chose drug, whereas 'choosers' always chose drug. The two groups were compared on their subjective responses to drug and on demographic variables. Ethanol decreased Arousal, Elation, Positive Mood and Vigor, and increased Anxiety, Depression and Fatigue in the non-choosers, whereas it increased Arousal and Vigor in the choosers. Ethanol choosers were also more likely to be males and/or full-time students than non-choosers. Diazepam produced sedative-like effects in both choosers and non-choosers, but markedly decreased Anxiety and increased Friendliness in choosers only. Diazepam choice was also associated with more frequent recreational use of marijuana and stimulants. Thus, both demographic variables and subjective drug effects were related to drug preference.

Subjective and cardiovascular responses to nicotine combined with caffeine during rest and casual activity

Although nicotine and caffeine have separately been shown to acutely increase subjective arousal, their combined effects are unclear. Furthermore, their effects during casual physical activity, the condition under which individuals usually experience nicotine and caffeine, are unknown. Smokers who were regular coffee drinkers (n = 19, 9 males, 10 females) participated in eight morning sessions, involving nicotine/placebo, caffeine/no caffeine, and rest/physical activity (i.e. 2 x 2 x 2 within-subjects design). Nicotine (15 micrograms/kg) or placebo was given via measured-dose nasal spray intermittently after consumption of decaf coffee with or without added caffeine (5 mg/kg), followed by subjective [Profile of Mood States (POMS), Stress-Arousal Checklist, visual analog scales] and cardiovascular (heart rate, blood pressure) measures. Casual physical activity was standardized by low-intensity bicycle riding while sitting comfortably. Results indicated significant subjective and cardiovascular effects of nicotine and caffeine individually, with the combination of nicotine and caffeine generally producing additive or greater than additive effects for each measure. However, activity mediated some of the subjective effects of nicotine, as nicotine appeared to be "stimulating" during rest but not during activity. There were no differences between males and females. These findings suggest that nicotine per se and caffeine generally have additive subjective and cardiovascular effects, and that nicotine may influence subjective stimulation differentially depending on whether a smoker is resting or engaged in casual activity.

Reinforcing effects of extended inhalation of a low nitrous oxide concentration in humans

The reinforcing, subjective, and psychomotor effects of 30 min of inhalation of 20% nitrous oxide were determined in 12 healthy volunteers using a choice paradigm with 100% oxygen as placebo. Nitrous oxide was chosen on only 22% of choice occasions, indicating that, in general, this concentration did not function as a reinforcer. Nitrous oxide produced changes in mood, but had no effect on psychomotor performance. Three out of the 12 subjects chose nitrous oxide on at least two out of the three choice sessions, and during a poststudy debriefing interview, reported pleasant effects of the drug. The other nine subjects reported unpleasant acute effects of the drug (e.g., drowsiness) or residual (postsession) effects of the drug which, they said, influenced their drug choice. The present results are compared to those results obtained in a previous study in which higher concentrations of nitrous oxide (30 and 40%) also produced relatively low choice rates. The apparent lack of reinforcing effects of extended inhalation of nitrous oxide is discussed.

Chronic and acute tolerance to subjective effects of nicotine

Tolerance to subjective effects of nicotine may induce novice smokers to increase the magnitude and frequency of their nicotine self-dosing. In this study, smokers (n = 8) and nonsmokers (n = 7) participated in three sessions involving presentation of 0, 7.5, or 15 micrograms/kg nicotine 30 min for 2 h via measured-dose nasal spray, with different doses presented on separate days. Subjective responses were assessed using visual analog scales (VASs) of jittery, light-headed, relaxed, dizzy, and head rush, and the Profile of Mood States (POMS) scales of vigor, confusion, fatigue, tension, and the composite scale of arousal. Smaller responses in smokers vs. nonsmokers were viewed as evidence for chronic tolerance. In addition, on each day subjects received a fifth, challenge dose of 30 micrograms/kg 30 min after the previous dosing. Smaller responses to the challenge dose as a function of increasing prior nicotine dosing during Trials 1-4 were viewed as evidence for acute tolerance. Results showed significant changes in most measures as a function of nicotine dose, and the dose-response curves for most VAS and POMS scales tended to be shifted to the right, or dampened, in smokers relative to nonsmokers, consistent with chronic tolerance. However, smokers and nonsmokers tended to respond to nicotine in opposite directions for POMS scales of vigor and arousal, perhaps reflecting withdrawal relief in smokers. Acute tolerance on a few selected VAS and POMS scales was apparent for both smokers and nonsmokers.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessing the behavioral effects and abuse potential of propofol bolus injections in healthy volunteers

Propofol is a recently introduced intravenous anesthetic agent, commonly administered to surgical patients because it induces anesthesia smoothly (i.e., provides loss of consciousness rapidly and usually with no complications) and is associated with rapid recovery. Propofol has psychoactive effects that could be construed as pleasant, although little abuse liability testing has been done on this agent in humans. Accordingly, we examined various effects of this agent at different subanesthetic doses (0.2-0.6 mg/kg) in order to characterize this drug's abuse potential (for recreational use or potential for diversion). Using a double-blind, randomized, crossover design, healthy normal volunteers (N = 10) were injected intravenously with the drug or with placebo. Before the injection and for up to 1 h afterwards, mood (including drug liking), memory and psychomotor performance were assessed. Propofol impaired memory and psychomotor performance and produced changes in 10 of 20 VAS mood ratings. Although there was variability in self-reported drug liking, some subjects clearly liked the effects of propofol, especially at the two higher doses. At the debriefing interview held after completion of the study, five subjects said if they had to participate in one more session in which they were given a choice between being injected with the highest dose (0.6 mg/kg) or a placebo, they would choose propofol. These preliminary results suggest that this agent may have some potential for abuse/diversion and perhaps stricter accountability procedures should be established for this drug in settings where general anesthesia or conscious sedation procedures are done.

Subjective, behavioral and physiological responses to intravenous meperidine in healthy volunteers

Meperidine is a mu opiate agonist that is frequently used to treat pain. We examined in healthy volunteers (N = 10) the effects of intravenous meperidine (0, 0.25, 0.5, and 1.0 mg/kg) on mood and psychomotor performance. A randomized, placebo-controlled, crossover design was used in which subjects were injected with meperidine or saline in a double-blind fashion. Subjects completed several subjective effects questionnaires commonly used in abuse liability testing studies before drug injection and at periodic intervals for up to 5 h after drug injection. Subjects also completed several psychomotor tests. Meperidine produced a constellation of subjective effects in a dose-related fashion, including increases in ratings of "sedated," "coasting or spaced out" and "feel drug effect" ratings. Many of the drug's subjective effects persisted up to 4 or 5 h after administration of the 1.0 mg/kg dose. Drug liking ratings assessed on a visual analog scale were increased after meperidine injection in about half of the subjects (P = 0.09). Eye-hand coordination was affected slightly by meperidine but other indices of psychomotor functioning were unaffected. Miosis increased in a dose-related fashion. Other physiological parameters, such as vital signs, were not affected by meperidine. We conclude that meperidine in healthy volunteers has robust and long-lasting effects on mood, but may have weaker effects on psychomotor performance.

Subjective and behavioral effects of diazepam depend on its rate of onset

This study addressed the assumption that rate of onset affects the euphorigenic effects of drugs. Drugs with rapid onset are commonly thought to be more euphorigenic than drugs with slower onset, but this idea has rarely been studied directly. Nine healthy male social drinkers, with no history of drug- or alcohol-related problems, participated in three sessions. On each session they received oral doses of placebo (PLAC), diazepam in a rapid onset condition (FAST), or diazepam in a slow onset condition (SLOW). In the FAST condition, they received a single 20 mg dose, whereas in the SLOW condition they received six 4 mg doses administered at 30-min intervals. Plasma levels of diazepam and desmethyldiazepam, subjective effects (including measures of euphoria), psychomotor performance and vital signs were monitored throughout each session. Although the FAST and SLOW conditions led to similar peak plasma levels of drug, the peak was attained earlier in the FAST condition (61 min versus 220 min). Subjects' scores on a measure of euphoria (MBG scale of the ARCI) were significantly higher in the FAST condition compared to the SLOW and PLAC conditions. Subjects exhibited significantly more behavioral signs of intoxication and greater psychomotor impairment in the FAST condition. Sedative effects of the drug were similar in magnitude, but the effects lasted slightly longer in the FAST condition. On several measures diazepam produced similar effects in the two conditions (e.g., ratings of strength of drug effect). These data provide limited support for the notion that a faster rate of onset of drug effects is associated with greater euphoria.

Lack of effect of social context on the reinforcing effects of diazepam in humans

The reinforcing effects of diazepam (DZP) were compared under two conditions in human volunteers using a cumulative dose procedure. Under the social (SOC) condition, groups of two to four subjects participated concurrently whereas in the solitary (SOL) condition subjects participated individually. During the first four sessions of each condition, subjects received 20 mg DZP in five divided doses (4 mg) in two of the sessions and placebo (PL) in the other two sessions. Each drug (DZP or PL) was administered in a distinctively colored capsule and labeled by letter code. During the last three choice sessions, subjects chose which capsule they wished to self-administer and were allowed to choose up to a maximum of seven capsules (28 mg DZP) during each session. Subjects also filled out questionnaires that assessed momentary mood. Overall, DZP was chosen on 33% of choice sessions and there were no differences across conditions. There was a tendency for choice to be correlated with levels of weekly alcohol consumption and liking scores, and as well the latter two measures were correlated. DZP produced sedative-like subjective effects that did not appear to be related to setting, choice of drug in the study, or alcohol drinking history. These results partially confirm previous reports of a relationship between DZP preference and alcohol consumption, but differ from previously reported studies in the overall lower level of DZP choice.

Self-administration of pentobarbital in light and moderate alcohol drinkers

Preference for a moderate dose of pentobarbital was assessed in light and moderate alcohol drinkers using a double-blind, placebo-controlled laboratory choice procedure. Sixteen light drinkers (less than six alcoholic drinks per week) and 13 moderate drinkers (six or more drinks per week) participated in a seven-session study in which they first sampled capsules containing pentobarbital (150 mg) or placebo and then chose and ingested the capsule they preferred. Subjective and behavioral measures were obtained at regular intervals during each session to characterize the drug's effects. Both groups chose pentobarbital less often than placebo: Mean pentobarbital choice in light drinkers was 20.8% and in moderate drinkers was 38.5%. Pentobarbital choice and drug liking ratings were highest among male moderate drinkers but still did not exceed placebo levels. The drug did not increase scores on standardized measures of drug euphoria, even among the most frequent choosers or the heaviest alcohol consumers. The results extend previous reports showing that individuals without histories of drug abuse, even those who are moderate consumers of alcohol, do not self-administer sedative/anxiolytic drugs or experience their effects as euphorigenic.