Human hallucinogen research: guidelines for safety.

There has recently been a renewal of human research with classical hallucinogens (psychedelics). This paper first briefly discusses the unique history of human hallucinogen research, and then reviews the risks of hallucinogen administration and safeguards for minimizing these risks. Although hallucinogens are relatively safe physiologically and are not considered drugs of dependence, their administration involves unique psychological risks. The most likely risk is overwhelming distress during drug action ('bad trip'), which could lead to potentially dangerous behaviour such as leaving the study site. Less common are prolonged psychoses triggered by hallucinogens. Safeguards against these risks include the exclusion of volunteers with personal or family history of psychotic disorders or other severe psychiatric disorders, establishing trust and rapport between session monitors and volunteer before the session, careful volunteer preparation, a safe physical session environment and interpersonal support from at least two study monitors during the session. Investigators should probe for the relatively rare hallucinogen persisting perception disorder in follow-up contact. Persisting adverse reactions are rare when research is conducted along these guidelines. Incautious research may jeopardize participant safety and future research. However, carefully conducted research may inform the treatment of psychiatric disorders, and may lead to advances in basic science.

Mystical-type experiences occasioned by psilocybin mediate the attribution of personal meaning and spiritual significance 14 months later.

Psilocybin has been used for centuries for religious purposes; however, little is known scientifically about its long-term effects. We previously reported the effects of a double-blind study evaluating the psychological effects of a high psilocybin dose. This report presents the 14-month follow-up and examines the relationship of the follow-up results to data obtained at screening and on drug session days. Participants were 36 hallucinogen-naïve adults reporting regular participation in religious/ spiritual activities. Oral psilocybin (30 mg/70 kg) was administered on one of two or three sessions, with methylphenidate (40 mg/70 kg) administered on the other session(s). During sessions, volunteers were encouraged to close their eyes and direct their attention inward. At the 14-month follow-up, 58% and 67%, respectively, of volunteers rated the psilocybin-occasioned experience as being among the five most personally meaningful and among the five most spiritually significant experiences of their lives; 64% indicated that the experience increased well-being or life satisfaction; 58% met criteria for having had a 'complete' mystical experience. Correlation and regression analyses indicated a central role of the mystical experience assessed on the session day in the high ratings of personal meaning and spiritual significance at follow-up. Of the measures of personality, affect, quality of life and spirituality assessed across the study, only a scale measuring mystical experience showed a difference from screening. When administered under supportive conditions, psilocybin occasioned experiences similar to spontaneously occurring mystical experiences that, at 14-month follow-up, were considered by volunteers to be among the most personally meaningful and spiritually significant of their lives.

Intravenous self-injection of four novel phenethylamines in baboons.

The present study evaluated the intravenous self-administration of four substituted phenethylamines, using a substitution procedure in baboons. Baboons were trained to self-inject 0.32mg/kg/injection cocaine under a fixed-ration (FR) schedule, with a 3h timeout following each injection. Doses of (+/-)-N-ethyl-3, 4-methylenedioxyamphetamine HCI (MDE), (+/-)-N-hydroxy-3, 4-methylendioxyamphetamine HCI (N-OH-MDA), (+)-N-N-dimethylamphetamine HCI (NNDMA), and 4-bromo-2,5-dimethyoxy-beta-phenethylamine (BDMPEA) and their vehicles were substituted for cocaine for 15 or more successive days. High doses of MDE and N-OH-MDA maintained self-injection; however, NNDMA and BDMPEA self-injection was less consistent. NNDMA did not reliably maintain self-injection, whereas one or more doses of BDMPEA maintained self-injection in each of three baboons. Intermediate to high doses of all four compounds decreased food pellet intake maintained under a FR schedule of reinforcement on a different lever. In some baboons, high doses of N-OH-MDA, NNDMA and BDMPEA produced signs of behavioral toxicity (e.g. cyclic pattern of self-injection, behavioral agitation, stereotypical movements) that were similar to those previously observed after administration of high doses of classic psychomotor stimulants such as d-amphetamine; however, the severity and profile of this behavioral toxicity differed between compounds. Thus, the present study documents both similarities and differences in the behavioral profiles of these four phenethylamines.

Caffeine reinforcement demonstrated in a majority of moderate caffeine users.

A mutually exclusive choice procedure was used to evaluate the reinforcing effects of caffeine in eleven normal subjects with histories of regular caffeine consumption (mean 256mg/day). Subjects participated for 24 weeks; each week consisted of three consecutive daily sessions (two sampling days followed by a choice day) during which subjects were required to abstain from dietary sources of caffeine. On each sampling day subjects ingested four capsules, one every 2h. Capsules contained placebo on one sampling day and caffeine (50 or 100mg/capsule) on the other sampling day. Placebo and caffeine were associated with different color-coded capsules. At the beginning of the choice day subjects chose one of the two color-coded capsules they wished to take on that day; they were required to ingest one capsule and, thereafter, they could ingest up to six additional capsules of the same color throughout the day. Across subjects and dose, caffeine was chosen over placebo on 80% of choice occasions; nine of 11 subjects (82%) chose caffeine on more than 70% of choice occasions and caffeine choice was replicable despite changes in capsule colors across blocks. This is the first study in a relatively uncontrolled outpatient context to demonstrate significant caffeine reinforcement in the majority of normal subjects.

Discriminative-stimulus effects of azaspirodecanedione anxiolytics in baboons trained to discriminate beta-carboline-3-carboxylic acid ethyl ester or pentylenetetrazole.

Baboons were trained to discriminate either pentylenetetrazole (PTZ) or beta-carboline-3-carboxylic acid ethyl ester (beta-CCE) from the no-drug condition. Both drugs specifically bind sites in the gamma-aminobutyric acid A (GABA(A)) receptor complex and decrease GABAergic transmission. beta-CCE occasioned drug-lever responding in baboons trained to discriminate PTZ and vice versa. Flumazenil, the benzodiazephine receptor antagonist, blocked beta-CCE, consistent with beta-CCE's receptor binding activity. The azaspirodecanedione anxiolytics buspirone and ipsapirone produced full generalization in all baboons; gepirone and tandospirone yielded full generalization in some baboons and partial in others. These anxiolytics are inactive in the GABA(A) complex and potently bind 5-HT(1A) sites. A specific 5-HT(1A) ligand, 8-hydroxy-2-(di-n-propylamino)tetralin, produced generalization similar to gepirone and tandospirone, which show the most specific 5-HT(1A) binding. The major azaspirodecanedione metabolite, 1-(2-pyrimidinyl)piperazine (an alpha(2)-adrenergic antagonist), occasioned the least drug-appropriate responding. Full generalization to buspirone and ipsapirone may have resulted from dopaminergic or alpha(1)-adrenergic activity combined with 5-HT(1A) activity. The molecular mechanism of the generalization profile for PTZ and beta-CCE shown by the present results is unclear. The data may reflect altered relationships between GABAergic and serotonergic transmission, and altered stimulus effects of the training drugs, in the context of chronically decreased GABAergic transmission.

Buspirone and lorazepam abuse liability in humans: behavioral effects, subjective effects and choice.

This study compared behavioral and subjective effects of two anxiolytics, the benzodiazepine lorazepam and the azaspirodecanedione buspirone, in healthy male volunteers with histories of sedative drug abuse. Placebo, lorazepam (1, 2, 4, 8mg/70kg) and buspirone (15, 30, 60, 120mg/70kg) were administered p.o. in a mixed sequence in a double-blind, cross-over design. Lorazepam, but not buspirone, decreased psychomotor/cognitive performance. Both drugs produced similar increases in ratings of drug strength, however the onset and offset times for lorazepam were later than for buspirone. Lorazepam increased ratings of liking in contrast to buspirone which produced negative mood-related subjective effects (e.g. increases in ratings of disliking, bad/unpleasant effects, and tension-anxiety). Lorazepam was categorized by subjects as producing effects similar to barbiturates or benzodiazepines in contrast to buspirone which was not. When subjects were given a choice between self-administering an intermediate dose of lorazepam (4mg/70kg) or buspirone (60mg/70kg), which produced similar ratings of drug strength, eight out of nine subjects chose lorazepam. This study provides the clearest human experimental evidence to date that the abuse liability of buspirone is lower than that of a prototypic benzodiazepine, even at supratherapeutic doses.

Tolerance to the discriminative stimulus effects of midazolam: evidence for environmental modification and dose fading.

The ability of behavioral variables to modify the development of tolerance to the discriminative stimulus effects of midazolam was evaluated. Rats were trained to discriminate 0.32mg/kg s.c. or 1.0mg/kg i.p. midazolam from no-drug, under a two-lever procedure, in daily experimental sessions consisting of multiple discrete 20-min trials: 15-min time-out, followed by 5-min under a fixed-ratio 15 schedule of food pellet delivery. Generalization testing was accomplished by administering progressively increasing doses of midazolam before each time-out period. During the chronic phases, twice daily injections of 10mg/kg midazolam or saline were given while discrimination training was either suspended or continued; generalization gradients for midazolam were determined weekly for 4 weeks. Chronic saline given when training was continued or suspended produced slight fluctuations in the midazolam minimal discriminable dose (MDD) (the first dose of midazolam in an individual generalization gradient to produce >/=90% drug-lever responding). Tolerance developed to the discriminative stimulus effects of midazolam when chronic midazolam was given while training was suspended: at Week 4, chronic midazolam produced 3-to 57-fold rightward shifts in the midazolam generalization gradient. In contrast, continued training during chronic midazolam produced no tolerance to the discriminative stimulus effects of midazolam: at Week 4 of chronic midazolam the MDD of midazolam was not different from pre-chronic and not different from either saline condition. The effects of chronic midazolam on stimulus effects and response rates were differentiated: despite tolerance to the stimulus effects of midazolam, there were no consistent changes in response rates during chronic midazolam administration.

Multiple-choice procedure: an efficient approach for investigating drug reinforcement in humans.

Two experiments demonstrated the efficiency of assessing drug reinforcement in humans by using a novel multiple-choice procedure. The distinguishing characteristic of the procedure is that it arranges intermittent reinforcement for choices between pairs of potential reinforcers. The procedure has three key operations: (1) a subject is exposed to the potential reinforcers; (2) a subject then makes two or more choices on a questionnaire; for each choice, the subject is required to choose one of two potential reinforcers (e.g. drug vs. drug choices and/or drug vs. money choices); and (3) subsequently only one of the choices, randomly selected, is reinforced. In the present experiments, two variations of the multiple-choice procedure were evaluated in twelve male drug abusers. Both experiments assessed the reinforcing effects of three drug conditions (200 and 400) mg/70kg pentobarbital and placebo) which were presented no more often than every to other day. The experiments demonstrated dose-related choice of pentobarbital over money as well as choice of a higher dose of pentobarbital over a lower dose or placebo. Orderly data were generated with a single-session exposure to each drug condition. Multiple-choice procedures should have applicability, not only to the investigation of drug reinforcement, but also to the study of non-drug reinforcement in humans.

Behavioral pharmacology of abecarnil in baboons: self-injection, drug discrimination and physical dependence.

The behavioral effects of abecarnil, a beta-carboline which has been suggested to function as a partial and/or selective agonist at the benzodiazepine receptor, were assessed in baboons. In a chronic administration study, 100mg/kg/day abecarnil for 6-8 weeks produced few signs of sedation: lip droop and intention tremor were observed in two of the four baboons. Flumazenil administration (5mg/kg, i.m.) on day 8 of chronic abecarnil produced only a mild precipitated benzodiazepine withdrawal syndrome. Vehicle substitution after 6-8 weeks of chronic abecarnil produced transient signs of a mild withdrawal syndrome, including decreased food intake, but did not produce vomiting, twitches/jerks or seizures. In a self-injection study, abecarnil (0.032-1.0mg/kg/injection) did not maintain rates of self-injection above vehicle control levels; higher rates of self-injection were maintained in the same animals by cocaine (0.32mg/kg/injection) and triazolam (0.01mg/kg/injection). The highest i.v. abecarnil dose (1.0mg/kg/injection) produced sedation and ataxia in two of the three baboons. In a drug discrimination study, generalization from lorazepam training conditions (1.8mg/kg, p.o.) to abecarnil was an increasing function of dose, and maximal drug lever responding occurred reliably in all baboons 5h after 10-32mg/kg, p.o. abecarnil administration. Flumazenil (0.32mg/kg, i.m.), given 4h after abecarnil, completely antagonized the abecarnil stimulus in test sessions 1h later. The present experiments show that the behavioral profile of abecarnil is clearly distinguisable from that of benzodiazepines.

Control of cigarette smoking topography: smoke filtration and draw resistance.

Systematic changes occur in the topography of puff and inhalation behavious as a cigarette is smoked. The role of various physical properties of the cigarette in controlling puff and inhalation behaviors was investigated in two experiments. The first experiment manipulated presmoking cigarette length while the second manipulated smoke filtration and cigarette draw resistance in an independent fashion. The characteristic progressive decrease in puff volume observed with each succeeding puff of a cigarette was not due to smoke satiation, fatigue, or visual cues. Although draw resistance can be a major determinant of puff volume, it did not appear to be a central mechanism accounting for the progressive decrease within normally smoked cigarettes. Rather, this decrease in puff volume appeared to be a response to the increasingly less filtered, more concentrated smoke. Although inhalation and exhalation volumes appeared weakly responsive to smoke satiation and/or fatigue, the subjective qualities of smoke "taste" and "satisfaction" also appeared to control these respiratory parameters. The present study provides some evidence suggesting that inhalation parameters may play a role in determining smoke exposure.

Dose-related caffeine discrimination in normal volunteers: individual differences in subjective effects and self-reported cues.

A within subject design was used to study a caffeine versus placebo drug discrimination in five volunteers who were not explicitly instructed that the drug conditions involved caffeine and placebo. The caffeine (200 or 300mg) versus placebo discrimination was acquired by all subjects and remained stable (78-90% accuracy) throughout the study which spanned 5 to 8.7 months across the subjects. A full caffeine dose-response function (50 to 400 or 600mg) was determined repeatedly under test conditions in each subject; caffeine produced orderly dose-related increases in caffeine identification in all subjects. The present study evaluated individual subject data to examine the correspondence between the subjective effects of caffeine versus placebo and the cues subjects reported as being important to making the discrimination. Although the subjective effects and self-reported cues differed across subjects, there was a correspondence within subjects. Prominent self-reported cues for caffeine included jittery/nervous/anxious (four subjects) and alert/active (one subject); self-reported cues for placebo included tired and/or headache (three subjects) and absence of drug effect (two subjects). The reporting of tired and headache as cues for the placebo condition suggests that caffeine withdrawal may produce stimulus effects relevant to the caffeine versus placebo discrimination.

Methocarbamol: evaluation of reinforcing and discriminative stimulus effects.

The behavioural effects of methocarbamol, a centrally acting muscle relaxant, were assessed using self-injection procedures in baboons and drug discrimination procedures in baboons and rats. The ability of methocarbamol to maintain self-injection was examined using a drug substitution procedure. Responding was maintained initially by cocaine delivery (0.32mg/kg/injection, i.v.). Each drug injection was followed by a 3-h timeout allowing a maximum of eight injections per day. Methocarbamol doses or vehicle were substituted for cocaine for a period of 15 or more days each, with re-establishment of responding under cocaine after each substitution. Evaluation of a wide range of methocarbamol doses (1.0-32mg/kg/injection) showed that this compound maintained rates of self-injection at vehicle control levels, which were below those maintained by cocaine. The discriminative stimulus effects of methocarbamol were studied in baboons trained to discriminate either lorazepam (1.8mg/kg, p.o.) or pentobarbital (10.0mg/kg, p.o.) from the no-drug condition and in rats trained to discriminate lorazepam (1.0mg/kg, i.p.), diazepam (1.0mg/kg, i.p.), or pentobarbital (10.0mg/kg, i.p.) from the no-drug condition using a two-lever, food-maintained drug discrimination procedure. Evaluation of a range of doses in baboons (10-180mg/kg, p.o.) and rats (32-180mg/kg, i.p.) showed that methocarbamol did not occasion drug-lever responding at any dose. Methocarbamol did not produce changes in response rates in baboons, but higher doses severely suppressed response rates in rats. The present experiments show that the behavioral profile of methocarbamol is clearly distinguishable from that of barbiturates and benzodiazepines. Taken together with analogous studies with other sedative-anxiolytic drugs, these results suggest that methocarbamol has a relatively low likelihood of abuse.