Flunitrazepam: a review of its pharmacological properties and therapeutic use

A comparison of five commercial immunoassays for the detection of flunitrazepam and other benzodiazepines in urine

Five commercially available immunoassay test kits (SYVA EMIT(R) d.a.u(TM), SYVA EMIT(R) II assay, Abbott FPIA, Cozart Auto-Lyte(R) and Roche Abuscreen(R) Online(TM), all used for the benzodiazepine group of drugs) were evaluated for their ability to detect flunitrazepam, its major urinary metabolite, 7-aminoflunitrazepam, and several other benzodiazepines at serial dilutions (final concentration 25-1000 ng/ml) in drug-free urine and in urines following oral administration of flunitrazepam (1-3 mg). For comparison, gas chromatography/mass spectrometry was used to measure urinary levels of 7-aminoflunitrazepam. Levels of drug detected in the study were compared with the cross-reactivities presented by the manufacturers for each individual kit. One to three mg doses of flunitrazepam were taken by volunteers and levels excreted in urine analysed over several hours. A positive response was obtained in several samples from volunteers who had taken 2 mg or 3 mg doses, but not a 1 mg dose. Thirty-five clinical samples from the individuals suspected of benzodiazepine abuse were also examined. The results were not consistent among the kits evaluated.We conclude that the test kits evaluated in this study do not detect flunitrazepam reliably, due primarily to their poor sensitivities.

Flunitrazepam and triazolam: a comparison of behavioral effects and abuse liability

The performance, observer-rated, and participant-rated effects of orally administered placebo, and two benzodiazepines, flunitrazepam (2, 4 and 8 mg/70 kg) and triazolam (0.25, 0.5 and 1 mg/70 kg), were compared in 14 sedative drug abusers using a double-blind crossover design. Both flunitrazepam and triazolam produced dose-related decrements in memory and psychomotor/cognitive performance, and increases in many participant- and observer-rated measures. Effects of flunitrazepam had an earlier onset and a longer duration than those of triazolam. Although there was evidence that the flunitrazepam doses selected for study were somewhat higher overall relative to the selected triazolam doses, analysis of the participant-rated measures collected 24 h after drug administration (next-day) suggests that flunitrazepam may have a greater abuse liability than triazolam when abuse liability is assessed 24 h after drug administration. The highest flunitrazepam dose produced effects that were significantly greater than those of the highest triazolam dose on next-day ratings of good effects, take again, and worth; all tested flunitrazepam doses produced effects greater than any triazolam dose on next-day ratings of liking and take again. The highest flunitrazepam dose, but no triazolam dose, significantly increased the maximum dollar value at which participants chose drug over money in a Drug versus Money Choice Procedure.

Quantification of flunitrazepam's oxidative metabolites, 3-hydroxyflunitrazepam and desmethylflunitrazepam, in hepatic microsomal incubations by high-performance liquid chromatography

A high-performance liquid chromatographic assay for the quantification of the oxidative metabolites of flunitrazepam, 3-hydroxyflunitrazepam and desmethylflunitrazepam, in human liver microsomal incubations was developed. Both metabolites were quantifiable in a single assay following a solvent extraction and reversed-phase high-performance liquid chromatography with UV detection. Standard curve concentrations for both metabolites ranged from 0.2 to 10 microM. Assay performance was determined using quality control samples and the intra- and inter-day accuracy and precision as determined by the coefficient of variations which were less than 15% (0.5-6 microM) for both metabolites. This method provides good precision and accuracy for use in kinetic studies of the oxidative metabolism of flunitrazepam in human liver microsomes.

An approach for dose finding of drugs in infants: sedation by midazolam studied using the continual reassessment method

AIMS

No drug has been demonstrated to provide simultaneously appropriate sedation, safety and lack of disturbance of the measured parameters during cardiac catheterization in infants. The objective of this study was to estimate the dose of midazolam, administered rectally, that would provide a 90% probability of adequate sedation in infants during cardiac catheterization. A sedation score > or =4 (six-point scale) 30 to 60 min after dosing was rated as a success.

METHODS

A double-blind, continual reassessment method using a Bayesian approach has been used. Sixteen infants were administered a single midazolam dose, within a 0.1 to 0.6 mg kg(-1) dose range.

RESULTS

Consecutive failures led to allocation of the highest dose to 15 out of 16 patients. The final estimated probability of failure of the 0.6 mg kg(-1) dose was 81% (95% CI: 78.5 to 84%). The time to reach a score > or =4 was longer than expected and the median duration-time at score > or =4 was shorter (15 min) than expected.

CONCLUSIONS

Delayed absorption and low rectal bioavailability may explain these data. Higher doses or different routes of administration may lead to the expected sedation, but the safety of doses higher than 0.6 mg kg(-1) administered rectally has not been evaluated. The therapeutic strategy for sedation of this category of infants in the hospital has now been changed based on the present results in that rectal midazolam has been abandoned in this indication.

Use and abuse of flunitrazepam

Flunitrazepam is not available in the US, and it is presently illegal to import it. Flunitrazepam has no therapeutic advantage over benzodiazepines presently marketed in the US. Its quick onset of sedation, amnesic properties, and additive effects with alcohol have led to its reputation as a party drug, club drug, or date rape drug. Several measures have been undertaken to curb its illicit use. It is unclear whether flunitrazepam poses a greater public health risk than other benzodiazepines.

Flunitrazepam and its involvement in date or acquaintance rape

An estimated 1 in 4 women in the United States will be raped in their lifetimes. Approximately 75% of all rapes are date or acquaintance rapes. Recently the illegal use of flunitrazepam (Rohypnol), a benzodiazepine, as a prelude to the assault has been reported. Flunitrazepam readily dissolves, and once in solution, is colorless, odorless, and tasteless. The predominant clinical manifestations are drowsiness, impaired motor skills, and anterograde amnesia. Due to the amnestic effects of flunitrazepam, historical clues of the rape event are difficult to obtain. Patients with a complaint of sexual assault who appear intoxicated or have anterograde amnesia should be suspected of unknowingly ingesting flunitrazepam. In addition to adhering to standard rape protocols, a urine specimen should be analyzed for flunitrazepam metabolites using gas chromatography/mass spectrometry. If the hospital, local, or forensic laboratory is unable to analyze for flunitrazepam, Hoffmann-La Roche Inc., the manufacturer of Rohypnol, should be contacted. Hoffmann-La Roche has a mechanism for definitive testing for flunitrazepam, at no cost, for health care providers, rape treatment centers, and law enforcement agencies. A network of organizations is attempting to reduce the abuse of flunitrazepam in association with date rape.

A comparison of the acute behavioral effects of flunitrazepam and triazolam in healthy volunteers

Flunitrazepam is an hypnotic benzodiazepine marketed in different European countries. Epidemiological studies have shown that it is frequently abused by opioid addicts. In a survey, "liking" scores for flunitrazepam in methadone maintenance patients were higher than ratings for other benzodiazepines. A double-blind, placebo controlled, crossover clinical trial was conducted to assess the acute behavioral effects of flunitrazepam (0.50 and 2 mg) and triazolam (0.25 and 0.50 mg) in healthy male volunteers. Drug effects on physiological measures, psychomotor performance, and subjective rating scales, including specific questionnaires to evaluate abuse liability (e.g., ARCI or "liking" scores), were assessed before and 6 h after drug administration. Flunitrazepam 2 mg produced the most intense disruptive effects on all the performance tasks, triazolam 0.50 impaired performance except balance. All study drugs at all doses produced sedation symptoms in all or part of the subjective effects questionnaires. Only flunitrazepam 2 mg induced significative increases in some of the scales ("liking", "good effects", "high") that could be related to a possible abuse potential. The results seem to indicate that flunitrazepam, when administered to healthy subjects, produces some pleasurable subjective feelings, that could indicate a higher abuse liability of this drug as compared with other benzodiazepines.

Interaction between erythromycin and the benzodiazepines diazepam and flunitrazepam

The effect of erythromycin on the pharmacokinetics and pharmacodynamics of diazepam and flunitrazepam was investigated in two randomized, double-blind, cross-over studies. Healthy volunteers ingested erythromycin for one week 500 mg t.i.d. On the 4th day they ingested a single 5 mg dose of diazepam (6 subject, Study 1) or 1 mg dose of flunitrazepam (5 subjects, Study 2), respectively. Plasma drug concentrations and psychomotor effects were measured during 42 hr after the ingestion of diazepam or flunitrazepam. In Study 1 erythromycin increased the area under the diazepam plasma concentration-time curve [AUC (0-42 hr)] by 15% (P < 0.05) and the concentration of diazepam in plasma at 42 hr by 63% (P < 0.05). The median peak concentration (Cmax) and the half-life (t1/2) of diazepam were increased but they did not change significantly (P = 0.17 and 0.12, respectively). Plasma N-desmethyldiazepam concentrations were slightly reduced during erythromycin treatment up to 8 hr (P < 0.05). In Study 2 the AUC (0-42 hr) of flunitrazepam was increased by 25% (P < 0.05) during the erythromycin treatment. The t1/2 of flunitrazepam increased significantly (P < 0.05), but the Cmax remained unchanged. The psychomotor effects of diazepam or flunitrazepam were not changed significantly by erythromycin. These pharmacokinetic interactions can be explained by the reduced metabolic elimination of diazepam and flunitrazepam. The interactions of erythromycin with diazepam and flunitrazepam seem to be slight and of limited clinical significance only.

High-performance liquid chromatographic procedure for the measurement of nitrobenzodiazepines and their 7-amino metabolites in blood

A simple and sensitive HPLC method is described for the determination of the nitrobenzodiazepines, nitrazepam, flunitrazepam and clonazepam and their respective 7-amino metabolites in post-mortem blood. Using a single-step extraction the nitrobenzodiazepines were recovered from 0.5 ml of blood using butyl chloride. The solvent was evaporated to dryness and the reconstituted residue injected onto an HPLC system. Separation was achieved using a phenyl-bonded reversed-phase column with an acetonitrile-phosphate buffer mobile phase. Ultraviolet detection (240 nm) was used for quantitation. A linear response was observed between 0.01 and 0.60 mg/l. Assay precision between and within assays was less than 20% for all analytes. The limits of detection ranged from 0.001 to 0.008 mg/l with a limit of quantitation of 0.01 mg/l for all analytes.

The influence of triazolam and flunitrazepam on isokinetic and isometric muscle performance

The influences of two benzodiazepines (triazolam 0.25 mg and flunitrazepam 2 mg) on isokinetic and isometric muscle performance and on cardiovascular parameters were examined after a standard period of sleep. A randomized and double-blind test procedure was used (n = 15). Triazolam had no significant (p < 0.05) influence on either of the test conditions. Administration of flunitrazepam significantly lowered values for maximal isometric force and for the cardiovascular parameters. It was concluded that triazolam does not influence performance. On the other hand, flunitrazepam does influence a number of strength characteristics and cardiovascular parameters in effort situations.

Amnesic effects and subjective ratings during repeated dosing of flunitrazepam to healthy volunteers

Flunitrazepam (1 mg) or placebo was administered once daily over a treatment period of 8 days to healthy, male volunteers to study the time course of the effects on memory functions and on subjective ratings of alertness and tension. The plasma level of flunitrazepam increased by approximately 40% (P < 0.05) during the treatment period. The mean pre-dose level of flunitrazepam on day 4 and day 8 was approximately 0.005 microM, and no residual effects on memory functions were observed. Intake of flunitrazepam decreased the number of freely recalled words by about 85% (P < 0.05) and significantly affected the subjects' rating of attention when tested during the first few hours after drug intake on day 1 of treatment. However, no significant effect on the subjects' rating of relaxation was observed. When tested similarly after 8 days treatment, flunitrazepam significantly affected the subjects' rating of relaxation (P < 0.01). Furthermore, no tolerance developed for the effect of flunitrazepam on free recall (P > 0.3) and the subjects' rating of attention (P > 0.7), and these effects had nearly equal time courses during the treatment period. This may indicate that the amnesic effect of benzodiazepines is at least partially mediated through the effects on attention or general arousal. Two of the subjects in the active drug group reported adverse reactions or incidents of discomfort during the 1st week following the treatment period, whereas none in the placebo group reported such reactions.

Simultaneous high-performance liquid chromatographic assay of droperidol and flunitrazepam in human plasma. Application to haemodilution blood samples collected during clinical anaesthesia

A simultaneous assay for droperidol and flunitrazepam by high-performance liquid chromatography has been developed and applied to blood samples collected during an acute normovolemic haemodilution under general anaesthesia. Haemodilution blood samples were stored at +4 degrees C to be transfused, if required, to a patient during the post-surgical phase. A C18 Supelclean cartridge was used for solid-phase extraction, and the recoveries were 74% and 89%, respectively, for droperidol and flunitrazepam. Compounds were chromatographed on a C18 Novapak column at 250 nm, with a mobile phase of acetonitrile-10 mM ammonium acetate buffer (pH 6.7) (45:55, v/v). Nitrazepam was used as the internal standard. For both drugs, the assay was linear up to 500 micrograms/l, and the detection limits were 20 and 10 micrograms/l for droperidol and flunitrazepam, respectively, and their observed levels in haemodilution samples were 93 +/- 82 micrograms/l and 76 +/- 107 micrograms/l, respectively. Some of the values for flunitrazepam were higher than the minimal efficient concentration, defined as the plasma level observed at the time of the patient wakening from anaesthesia (12 +/- 4 micrograms/l). According to our results, haemodilution sampling can be performed before induction of anaesthesia. When the blood is collected after the anaesthetic induction, it seems necessary to determine levels of the two drugs in haemodilution samples to avoid side-effects.

High-dose flunitrazepam anesthesia

Benzodiazepines have receptors in the nervous system as well as in the kidney, liver, skeletal and ileal muscle, lungs and the heart. Flunitrazepam is a benzodiazepine with pronounced hypnotic effects in the usual dosage. High dose flunitrazepam anesthesia is suggested for prolonged surgical procedures as an alternative to the well known high-dose opiate anesthesia. Its reversal using flumazenil can shorten the post-operative anesthetic effect.

A comparison of the physical dependence inducing properties of flunitrazepam and diazepam

Dogs dosed chronically (4-7 weeks) with oral flunitrazepam (7.6 mg/kg/day) or diazepam (24-36 mg/kg/day) administered in 4 equally divided doses had dose-related flumazenil precipitated benzodiazepine abstinence scale scores (BPAS) of comparable intensities despite the fact that plasma levels of flunitrazepam and its metabolites were much lower than nordiazepam levels in the diazepam-dependent dog. Both groups of dependent dogs had clonic and tonic-clonic seizures after oral and IV flumazenil. Precipitated abstinence signs persisted longer in the diazepam than in the flunitrazepam-dependent dogs. Differences in the pharmacokinetics of the drugs of dependence, their metabolites, and their interactions at receptor sites offer a partial explanation for the high level of dependence seen in the flunitrazepam dog. The finding that the estimated plasma free concentration of flunitrazepam and its metabolites is equal to or greater than that of diazepam and its metabolites together with the fact that flunitrazepam has a higher affinity for the benzodiazepine receptor than either diazepam, nordiazepam or oxazepam can explain why the intensity of the precipitated abstinence syndrome is comparable in flunitrazepam- and diazepam-dependent dogs. Although the flumazenil-induced precipitated abstinence syndromes observed in flunitrazepam- and diazepam-dependent dogs differed qualitatively they did not differ quantitatively. It is therefore concluded from these data that the doses of flunitrazepam and diazepam, chosen for producing comparable degrees of weight loss during dose escalation, did not differ in the degree of physical dependence that they produced in the dog.

Inter- and intraindividual variability in the concentration-effect (sedation) relationship of flunitrazepam

1. The relationship between plasma flunitrazepam concentrations and the degree of sedation was evaluated in 20 healthy subjects receiving two single oral doses of 1 mg flunitrazepam on two different occasions (1 week apart). The degree of sedation was rated blindly during the two treatment sessions in parallel with blood sampling (48 h). 2. A strong correlation between the concentrations of flunitrazepam in plasma and the degree of sedation was found according to the sigmoid Emax model. The plasma drug concentration producing 50% of maximal effect (EC50) was found to be 7.0 and 6.5 ng ml-1 on the two occasions, respectively. The variability in EC50 between subjects was larger (C.V. 39%) than the variability within subjects (C.V. 27%). 3. The steepness of the concentration-response curve as reflected in the slope factor(s) showed a virtual 'all or none' response to flunitrazepam with s values ranging from 3 to 30 with a mean of about 14. 4. The results in young healthy subjects suggest that the present dosage recommendations for temporary insomnia (1-2 mg) may be inappropriate; the dose can probably be reduced to 0.5 mg in some patients to achieve moderate sedation.

Pharmacokinetics of flunitrazepam following single dose oral administration in liver disease patients compared with healthy volunteers

The pharmacokinetic behaviour of flunitrazepam and its main active metabolite, N-desmethyl flunitrazepam, was investigated in 12 patients with liver disease (cirrhosis or hepatitis) compared to 6 healthy volunteers. A gas-liquid chromatographic method allowing for simultaneous determination of flunitrazepam and N-desmethyl flunitrazepam in plasma samples was developed. The accuracy and the precision near the quantification limit of ca. 1 ng/ml were better than 5%. Plasma levels of flunitrazepam were not significantly altered by hepatic failure, whereas plasma levels of N-desmethyl flunitrazepam were lower in patients than in healthy subjects. Pharmacokinetic parameters did not differ significantly between healthy subjects and liver disease patients: the oral clearance was 3.5 +/- 0.8, 3.5 +/- 1.9 and 4.0 +/- 1.2 ml/min/kg, respectively in healthy subjects, patients with hepatitis and patients with cirrhosis. The apparent elimination half-life was 22 +/- 5 h in healthy subjects, 25 +/- 10 h in patients with hepatitis and 20 +/- 6 h in patients with cirrhosis. However, the expected increase of the drug free fraction during liver disease could decrease the therapeutic and toxic ranges of flunitrazepam in these patients.

Antagonism of flunitrazepam-induced sedative effects by flumazenil in patients after surgery under general anaesthesia. A double-blind placebo-controlled investigation of efficacy and safety

This study aimed to assess the efficacy and safety of flumazenil and a placebo in reversing the residual effects of flunitrazepam used to induce anaesthesia for elective laparoscopy in 49 female patients aged 16 to 52 years. In contrast to the placebo, flumazenil gave reductions in amnesia, sedation score, mood rating for mental sedation and physical sedation, and time taken to complete a psychomotor performance test which lasted throughout the study. There were no significant changes in pulse rate, respiration rate or blood pressure, and no unwanted effects were attributed to flumazenil.

Cutaneous and subcutaneous blood flow during general anaesthesia

The vasodilator effect of anaesthetic agents on cutaneous vessels has often been investigated. In contrast, although subcutaneous tissue is concerned with metabolism and thermoregulation, the effects of anaesthesia on subcutaneous blood flow have not been well documented. The purpose of this study was to determine the magnitude of changes in cutaneous and subcutaneous blood flow during general anaesthesia in Man. Anaesthesia was induced with flunitrazepam in 15 patients before facial plastic surgery. Blood flow was estimated using heat thermal clearance (HC). Two HC sensors in different areas allowed the measurement of superficial and deep HC. Systolic (SABP), diastolic (DABP) and mean arterial blood pressure (MABP), heart rate (HR), and rectal and mean skin temperature were also recorded. After induction of anaesthesia, HR increased significantly (p less than 0.05) whereas SABP, DABP and MABP remained unchanged. The rectal-toe temperature gradient fell from 6.3 +/- 4.1 degrees C to 3.4 +/- 1.1 degrees C (p less than 0.01) suggesting a reduction in vasomotor tone. Superficial HC increased from 0.37 +/- 0.06 to 0.42 +/- 0.08 W.m-1.degrees C-1 (p less than 0.05) whereas deep HC decreased from 0.33 +/- 0.07 to 0.31 +/- 0.09 W.m-1.degrees C-1 (NS) and returned to the control value thereafter. Rectal temperature and mean skin temperature were unchanged. The changes in deep HC are similar to those previously observed in muscle during induction of anaesthesia. Our results show that anaesthesia mainly affects cutaneous blood flow, without any significant change in subcutaneous blood flow during the early phase of anaesthesia in human beings.

Pharmacokinetics of flunitrazepam in rats studied by a radioreceptor assay

In rat the kinetics of flunitrazepam (FNZ) was evaluated by a radioreceptor assay (RRA) after i.v. administration of 1 mg/kg and after oral administration of 1 and 3 mg/kg. The i.v. kinetics is biexponential and the g.i. absorption is very rapid (with a plasma peak at 0.25 hour) with a good bioavailability (69%); the apparent distribution volume is high, 4.8 L/kg; the half-life is equal to 3.5 hours; the elimination constant is equal to 0.8 h-1; the urinary excretion of FNZ-equivalent is negligible; the plasma total clearance is equal to 3.9 (L/kg)h-1. The concentrations of FNZ-equivalents after oral administration of 1 mg/kg show a peak at the 2-nd hour with a very high concentration in the following organs (in decreasing order): brain, kidneys, heart, liver; after 8 hours no FNZ-equivalents are present in these organs except in the brain, which shows detectable concentrations at the 32-nd hour. The peak concentrations of FNZ-equivalent in brain, kidneys and heart are higher than the corresponding peak concentration in plasma.

Oral flunitrazepam in the prevention of local anaesthetic-induced convulsions in mice

The present study determined whether oral flunitrazepam was effective reducing CNS toxicity of lidocaine and bupivacaine. Pretreatment of mice with flunitrazepam, 0.065-0.25 mg X kg-1, significantly reduced or prevented convulsions and mortality induced by lidocaine 106 and 209 mg X kg-1 or bupivacaine 58 and 90 mg X kg-1 injected intraperitoneally. The doses of flunitrazepam used did not cause measurable sedation in mice. The efficacy of oral flunitrazepam in preventing local anaesthetic-induced convulsions is similar to that previously reported by intraperitoneal or intramuscular injections in mice. Flunitrazepam could be useful for oral premedication of patients before regional anaesthesia.

The comparative effects of benzodiazepines, progabide and PK 9084 on acquisition of passive avoidance in mice

Acquisition of passive avoidance following aversive conditioning to a dark compartment was measured in mice under the influence of one of seven benzodiazepines, the GABA-mimetic drug progabide or PK 9084, a nonbenzodiazepine ligand on benzodiazepine receptors. The drugs were administered prior to the training trial and retention was measured in the absence of the drug 24 h later. Oral administration (dose in mg/kg in parentheses) of flunitrazepam (0.1), lorazepam (1.0), nitrazepam (3.0), diazepam (10), flurazepam (10) and chlordiazepoxide (30), all prevented retention whereas progabide (100-800) and PPK 9084 (10-100) were ineffective. In comparison to effects on motor capacity none of the benzodiazepines was outstanding in its acquisition interfering effects.

A placebo-controlled, dose-ranging study comparing 0.5 mg, 1 mg and 2 mg flunitrazepam in out-patients

A placebo-controlled, dose-ranging study was carried out in 18 patients, aged under 65 years, with sleep disturbance to compare the hypnotic effects of 0.5 mg, 1 mg and 2 mg flunitrazepam and placebo. Patients received each treatment in random order for 7 days. Assessments by both doctor and patients were made on entry and at the end of each treatment period. The results showed that the 1 mg flunitrazepam dose was optimal with respect to speed of action, duration of action, quality of sleep and lack of residual clinical sequelae.

Flunitrazepam increases and diazepam decreases the lower oesophageal sphincter tone when administered intravenously

Increasing the resting lower oesophageal sphincter tone is an accepted method of reducing the risk of gastro-oesophageal reflux. The effect of intravenously administered flunitrazepam and diazepam on the lower oesophageal sphincter tone were studied in 16 healthy subjects. Flunitrazepam increased this tone significantly (p < 0.05) while diazepam decreased the tone, also significantly (p < 0.005). Intravenous flunitrazepam may be a valuable sedative or premedicant, especially in patients who may develop gastro-oesophageal reflux.

Residual effects of repeated doses of 0.5 and 1 mg flunitrazepam

9 normal subjects were tested on a large battery of tests the morning after a hypnotic dose of flunitrazepam (0.5 mg and 1 mg) and a placebo. Each drug was given for 8 nights and assessments were made 10 and 13 h later on days 1, 4 and 8. Self-ratings of sleep were made every morning. The tests comprised mood and bodily symptom self-ratings, taping rate, visual reaction time, symbol copying and substitution tests, critical flicker fusion threshold, digit span and cancellation test. The EEG was recorded under eyes open and eyes closed conditions and analysed using broad waveband filters. Subjectively, the 0.5 mg dose was associated with increased alertness, contentment and calmness, the 1 mg dose with minimal decrease in alertness and contentment. Sleep onset was accelerated by flunitrazepam initially but effects on quality of sleep were not major due to subject selection. The 1 mg dose occasionally impaired performance on tapping, symbol copying and substitution and critical flicker fusion. The 0.5 mg dose marginally impaired symbol substitution and improved symbol copying. The EEG showed definite dose-related effects which tended to increase over the 8 nights of ingestion of the drug. It is concluded that whereas the 1 mg dose may sometimes be associated with definite residual effects the next day, the 0.5 mg dose possesses positive qualities in producing useful subjective effects the next day without appreciable impairment of psychological performance.