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Major Studies of Drugs and Drug Policy
Marihuana, A Signal of Misunderstanding - Table of Contents

The Report of the National Commission on Marihuana and Drug Abuse

Effects of Short-Term or Subacute Use



Studies have only begun in this area in the last 10 years. Subacute toxicity studies in rats involving 30 daily intraperitoneal injections of up to 30 mg/kg THC were recently reported by Phillips et al. (1971). No fatalities were observed. Total body and organ weight (rains were significantly retarded over the period. However, no significant differences in organ histology were detected although in a few animals there were suggestions of change in liver and testicular cells. An interesting phenomena also observed was a suggestion of increased sensitivity to effects of Delta 9 THC occurring after two weeks of daily treatment.

Thompson et al. (1971) under contract to NIMH studied the toxicity in rats treated daily for seven, 28, 91 and then 119 days with oral Delta 9 THC, A" THC and crude marihuana extract at doses from 50 to 500 mg/kg. The findings were generally similar for all three preparations although A" effect was greater than All THC which in turn was greater than CME.

A bimodal pattern of behavorial toxicity was exhibited by the cannabinoids for all time periods of dosing ranging from five to 119 days. Initially, a dose-related generalized central nervous system depression was noted. This was characterized by huddled posture, inactivity, drowsiness, slow movements, unkempt appearance, loss of appetite, wide stance, constipation, weight loss, depressed respiration and heart rate and fall in body temperature. Tolerance gradually developed to the initial depressant effects starting after two to five doses and continued at different rates for different parameters.

Concomitant to the development of tolerance, rats exhibited progressively more hyperactivity, manifesting increased exploratory behavior, grooming and motor activity. The daily duration of the altered behavior progressively shortened. Tolerance to the hyperactivity was not seen in the rats. Later, in the experimental period, the rats became hyper-irritable and exhibited fighting behavior, especially at lower doses. Additionally, tremors and later chronic convulsions occurred in significant numbers of rats.

The onset and frequency of chronic convulsions were dose-related and the severity increased as the duration of dosage was extended. Cumulative toxicity, as evidenced by increased mortality, was observed in the rats but most deaths and maximal toxicity (central depression) occurred 36 to 72 hours following first treatment. Drug dose-related histopathological changes in all treated rats (in addition to decreased body and organ weight gains) were hypocellularity of the spleen and bone marrow, vacuolization of the adrenal gland and degeneration of the testes (seminiferous tubules) or ovarian stronia. Extended doses from five to119 days were not significantly more toxic except to the adrenals. No evidence of abstinence syndromes were noted upon abrupt cessation of these doses.

Similar behavorial and clinical findings were observed in monkeys given 50-500 mg oral Delta 9 THC, All THC and equivalent CME for up to 91 days. Cumulative toxicity was less severe and all monkeys survived the initial moderately severe central nervous system depression. Tolerance to the depression occurred and the monkeys returned to their undrugged behavior. Mild hyperactivity was noted only in several of the median dosed animals.

Three of 28 monkeys studied became moribund on days 10, 14 and 16 respectively. These were sacrificed and the only histopathology seen was severe hemorrhagic and probably drug-related enterocolitis. The bone marrow and kidney changes seen probably were due to severe electrolyte imbalance resulting from the intestinal lesion. The thymus lesion is consistent with stress due to this electrolyte imbalance. Pancreatic atrophy was due to weight changes. Eight additional monkeys were sacrificed at 28 days in fair-to-good condition and no histopathology was demonstrable. Several other monkeys had bloody diarrhea, but recovered spontaneously without demonstrable histopathology.

The remaining 17 monkeys were all in fair-to good condition at 28 days and hyperactivity was no longer observed. They were treated at the same dose for an additional 63 days. Tolerance to the central depression continued to develop so that the effects lasted only one to two hours at 91 days. No additional monkey fatalities were recorded -and the remaining 17 monkeys were normal histopathological at autopsy. Urine and ophthalmological examinations were all within normal limits. Hematological and blood chemical changes after 28 and 91 days were minor and little affected in the surviving monkeys.

Thus, a. minimal toxicity in monkeys, either physical or behavorial, is evident after 91 daily doses orally of enormous amounts of Delta 9 THC. However, significant cumulative toxicity, primarily a generalized central nervous system depression, is evident in the first few days but tolerance rapidly develops to these effects. A dose-related hemorrhagic enterocolitis occurred which may lead to electrolyte imbalance and death in a few monkeys. This probably is a direct irritative phenomena.

Again, the enormous daily doses of THC that were administered to these animals cannot, be compared to the daily doses used in man even by the heaviest users.

The effects were observed of 28 daily administrations to monkeys of intravenous Delta 9 THC in sesame oil-Tween 80-saline vehicle at doses of 5, 15 and 45 mg/kg. Behavioral, clinical, hematological and hemochemical changes were similar for monkeys given single or repeated injections. However, the duration was extended in the 28-day groups and tolerance gradually developed. Delayed death indicative of cumulative toxicity occured on days eight and 19 in two of four animals given the largest dose.

Histopathological changes, noted in the two animals which succumbed and in one of the highdose monkeys, were acute hemorrhagic pneumonia resembling the finding in the single-intravenous studies at doses of 128 mg/kg or greater. Additionally in the repeated dose study, edema, ulceration and fibrosis at the injection sites probably contributed to minor hematological and hemachemical alterations.

In summary, the 1972 Marihuana and Health Report to the Congress from the Secretary of HEW noted that these doses were employed in rodents and mammals to test the limits of toxicity. The doses are much higher than those used by man and the routes of administration substantially dif ferent. These studies have shown that the margin of safety between the lethal dose and the pharmacologically active doses of Delta 8 and All THC and crude marihuana extract is large. Consequently, it has been determined that these compounds could be safely administered to man for Phase I and early Phase II clinical studies (Secretary of HEW, Feb. 11, 1972, p. 158-160).


Only a few investigators have studied the subacute administration of marihuana to man. Marihuana cigarettes of unknown potency were made available to 34 military prisoners in Panama by Siler et al. (1933). The mean daily consumption was five cigarettes (range one to 20). The usual behavior effects associated with marihuana use were noted. No ill effects were observed nor abstinence syndrome seen.

Williams et al. (1946) made available marihuana cigarettes of unknown potency to six prisoner addicts who were experienced marihuana users in the Public Health Service Lexington Hospital. The subjects were permitted to freely consume the drug in any quantity desired. The number of cigarettes consumed increased only slightly over a 39-day period. The daily range was from nine to 26 per day with a mean of 17. Only minimal evidence of tolerance was seen. There was no evidence of physical dependence; that is, no observable abstinence, syndrome was observed after abrupt termination of the drug.

In general, the following observations were made on these subjects: daily rectal temperature increased slightly; pulse, rate increased for three weeks, then returned to normal; no change was noted in respiratory rate, coordination, or rote memory ; increase was noted in sleep and body weight while caloric intake initially increased then progressively decreased; mild confusion was observed; general intelligence tests were slightly impaired while psychomotor tests were performed faster but less accurately; EEG showed inconsistent changes but returned to normal five days after cessation; and mood was euphoric for several days followed by general lassisitude and indifference.

In a recent uncontrolled preliminary study (Personal Communication, 1970), marihuana extract was administered daily to eight terminal cancer patients from four to 13 days (mean 8.5 days). Daily doses were purposefully raised by the investigator from 7.5 mg (mean daily dose 19.8 mg THC). The total dose per individual patient averaged 168 mg with a range from 75-210 mgs.

Euphoria was experienced by all eight subjects and one had a transient anxiety episode at a high dose. Three subjects demonstrated decreased-opiate analgesic needs indicating an analgesic-effect of the drug. Five subjects reported improved appetite and five, of six tested, demonstrated objective improvement in depression on Back scale. No new changes were seen in physiological parameters, neurological status, blood cell and chemistry values or urine examination. During the period of drug effect, drowsiness was common but not lethargy, lassitude or indifference. In fact, all became more active on the ward. No evidence of abstinence symptoms were seen after abrupt discontinuation of the drug.

Volavka et a]. (1971) in preliminary experiments administered two marihuana cigarettes daily (13 mg Delta 9 THC) to four detoxified heroin addicts. Pleasant effects peaked during the second week and then leveled off. Prominent dysphoric effects and depressive reactions with paranoid thoughts appeared during the third to sixth days and persisted causing cessation of the study by one subject after 10 days and after 17 days by another. The other two subjects completed the entire planned 22 days.

Again no abstinence syndrome was seen and the dysphoric symptoms disappeared within five days after the last dose. Consistent electroencephalogram changes developed in three of four subjects indicating increased synchronization. Their EEG changes first appeared immediately after smoking.

In two of the f our subjects they were detectable, in the presmoking records after days 12 and eight, and did not begin to subside until 48 hours after the last dose in two subjects and persisted for the entire 72 hours follow-up in a third subject.

Fink et al. (1971) subsequently studied five medical and graduate students who had been almost daily marihuana smokers in college and were currently weekend smokers. Each subject smoked under laboratory conditions one marihuana cigarette containing 14 mg of THC each morning daily for 21 days.

No subject reported any adverse effects from smoking. The subjects were generally able to conduct their usual daily activities including jobs. However, they reported they did not function completely up to par during the several hour duration of the acute drug effect. There were no effects which persisted for more than three to five hours and cumulative effects were not noted day to day. No persistent decrements were seen in behavior, mental status, EEG, heart, rate, short-term memory, or psychomotor function tests. In sum, daily marihuana smoking for 21 days was well tolerated by well-adjusted graduate students.

Mendelson et al. (1972) performed a Commission-sponsored study of the biological and behavioral concomitants of 21 days repeated doses of marihuana. Subjects were individuals whose life style, activities, values and attributes were more characteristic of the unconventional youthful subculture than most of their peers in the general population. Their mean age was 23. Based on I.Q. testing they were superior intellectually although they had completed, on the average, two-and-a half years of college. Their job histories were rather erratic and characteristic of a pattern of itinerant living. Their family background was a middle or lower-middle socioeconomic status. In addition alcohol use was infrequent while use of drugs, especially hallucinogens and amphetamines, was significant.

Two groups of 10 subjects each were investigated over separate 31-day periods of confinement on a comfortably furnished research ward equipped with an array of recreational materials. A large, open yard was available for outdoor recreational activities. The research period was divided into three periods: a pre-drug period of five days during which the subjects were drug free; a, subsequent 21-day period when marihuana, could be earned by performing a, work-contingent operant task, then purchased and smoked on a free-choice basis; and a five-day post-drug period without access to marihuana.

All attempts were made to not interfere in any way with performance of the operant task or free choice marihuana smoking although the subjects were under constant observation. A vast array of behavioral and biological assessments were made during the experimental period to determine any effect of repeat doses of marihuana over this time.

Two groups of subjects, studied separately, differed primarily in the frequency of marihuana smoking over the past year. Both groups had averaged about five years of marihuana use (range two to 17 years). The first group studied, referred to as the "casual" users by the authors, reported an average frequency of marihuana use, of 7.7 occasions per month (range three to 15 occasions). The second group studied, referred to as the "heavy" users by the authors, reported almost daily use of marihuana (average 33 sessions per month; range 20+ to 75, including one substitute subject to fill the group who only smoked about 10 times a month).

During the first 20 days of the smoking period, the casual group's consumption averaged three cigarettes daily (individual average was one-half to six) while that of the heavy users averaged six-and-a-half cigarettes daily (individual average three to eight-and-a-half). Both groups demonstrated a, progressive trend toward increased daily consumption during the experiment. Close examination of the consumption patterns for individual subjects showed that the trend toward increased use occurred in the subjects who were initially the heaviest users. Several subjects who were initially the least frequent users did not increase their use of marihuana over the course of the study.

Subjects in both groups tended to smoke practically all of each cigarette including the butt. Each cigarette contained about 20 mg- Delta 9 THC. Therefore, the heavy users average daily intake was 130 mg of THC or a total of almost, Joni- -grams of THC over the 21-day period. The casual users average intake was slightly less than half this amount.

No abstinence syndrome or physical dependence was observed after abrupt termination of smoking. Signs of mild to moderate psychological dependence. were possibly seen in the heavy group but no evidence of psychological dependence was seen in the casual users.

No consistent clinically significant physiological or biochemical changes were demonstrated during or after the period of repeated use of marihuana.

Urinalysis, complete blood counts, cell morphologies and differentials, and blood chemistry determinations (calcium, phosphorous, glucose, blood urea nitrogen, uric acid, cholesterol, total protein, albumen, total bilirubin, alkaline phosphatase, lactic dehydrogenase, and serum glutamic oxalacetic transaminase) were unaffected.

Weight gain occurred in all but one subject. Maximal gain was seen during the marihuana smoking period. The subjects were not judged to be clinically malnourished prior to the experiment.

Normal body temperature was not altered. No significant change, in pulmonary function (decreased. vital capacity or acute broncho spasm) was observed during the marihuana smoking period.

Variable inconsistent changes in upright blood pressure were noted. Effects on pulse rate were related only to acute drug administration and were more pronounced during the initial smoking phases. This suggests that tolerance developed to drug-induced tachycardia. No significant electrocardiographic changes were observed. Marihuana smoking had no apparent effect on exercise related cardiac vascular function.

Physical examinations revealed only the development of persistent conjunctival injection, lateral gaze nystagmus and fine, finger tremors. These findings were believed to be acute drug effects and of no clinical significance. No signs of neurological abnormality were observed. No cumulative effect of marihuana to cause, impairment of cognitive function was noted on a battery of tests sensitive to organic brain function.

An increased amount of sleep in both shorter and longer blocks of consecutive hours was observed. Also an increase in the number of discrete episodes of sleep, especially one to three hour episodes also occurred during the marihuana use period. Reappearance of pre-drug pattern was seen during the post-drug period. This reversion appeared to begin toward the end of the drug period which may be indicative of tolerance, to the acute depressant-like effects of marihuana.

Generally, performances on short-term memory, psychomotor skills and time estimation suggests that repeated marihuana smoking had no discernible effect on the ability to improve performance with practice on these measures. Tolerance appeared to develop to the acute decrement in performance on these measures. On the time estimation task, a tendency appeared for the subjects to increasingly overcompensate for the acute drug effect with repeated testing in the nonintoxicated state.

Both casual and heavy users had a marked decrement in total social interaction during the first portion of the marihuana smoking period. Total interaction of the casual subjects continued to diminish subsequently. Heavy users subsequently tended to exceed presmoking levels of interaction indicating they accommodated to the depressant effects of repeat doses of marihuana.

Both groups became progressively more convivial and less task-oriented in group discussions. They offered less suggestions in problem-solving tasks but continued to efficiently solve the problem.

Casual users reported general relative increases in negative daily moods and decreases in positive daily moods during the course of the study. The trend began with the onset of smoking and persisted through the post-smoking period. This trend could be a sequelae of repeated marihuana use or related to non-drug variables (set and setting).

The heavy users did not evidence this trend toward relative increases in dysphoric mood until the post-smoking period. Again this may be related to repeated marihuana use, reflect psychological dependence or be related to set and setting variables, such as boredom and tension associated with the prolonged study period.

Finally, repeated use of marihuana over the 21day period did not decrease motivation to engage in a variety of social and goal-directed behaviors. Almost without exception, every subject earned the maximum number of points every day throughout all non-drug and drug periods. No consistent alteration in pattern of work could be related to repeated marihuana use. Subjects often performed very high work output while they were smoking marihuana and experiencing the maximum drug effects.

Repeated marihuana use, did not decrease subject's motivation to complete the study. Nor was any noticeable effect observed on interest and participation in a variety of personal activities, such as, writing, reading literature, keeping up with current national and world events, and participation in both athletic and esthetic endeavors.


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