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Effects of Long-Term Cannabis Use

 

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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


DEPENDENCE AND TOLERANCE

Neither severe physical dependence, nor prominent withdrawal symptoms after abrupt
termination of very heavy usage is suggested by some overseas experience (Charen and
Perelman, 1946; Fraser, 1949; Ludlow, 1857, Marcovitz and Myers, 1944; Siler et al., 1933;
Walton, 1938). Other studies, however, suggest marked psychological dependence from heavy
use producing compulsive drug taking in very heavy users (Indian Hemp, 1893; Chopra and
Chopra, 1957; Bouquet, 1944; Lambo, 1965).

Psychosomatic abstinence syndromes often reported were physical weakness, intellectual
apathy, loss of appetite, flatulence, constipation, insomnia, fatigue, abdominal cramps
and nervousness, restlessness, and headache. For most heavy users the syndrome of anxiety
and restlessness seem to be comparable to that observed when a, heavy tobacco smoking
American attempts to quit smoking.

However, the psychological dependence appears to be severe as evidenced by the f act
that one group of subjects were unable to cease their habitual use although the frequency
of use, was only eight to 12 times per month (Soueif, 1967). This psychological dependence
may have made some users claim physical dependence so that the government did not
terminate dispensing them their drug. Studies in the United States using must lower doses
for shorter periods of time have revealed little if any evidence of psychological
dependence (Bromberg, 1934 Mayors Committee, 1944; Williams et al., 1946).

Tolerance to the subjective and depressant effects of the drug (discussed in an earlier
section) does probably occur in man, with heavy use. Thus, increasingly larger and more
frequent doses become necessary to experience the desired effects.

Several investigators have recently studied the question of physiological and
psychological dependence to Delta 9 THC in monkeys using intravenous self-injection
techniques.

Deneau and Kaymakcalan (1971) demonstrated that no monkey initiated self-administration
over a three-week period when given the opportunity to self-inject a behaviorly effective
dose of 100 micrograms per kilogram of Delta 9 THC in a Tween solution. The researchers
subsequently administered to these monkeys this dose every six hours. Tolerance developed
to the behavioral effects within a few days. Dose administered was progressively increased
up to 400 micrograms per kilogram over the course of a month. When the injections were
abruptly discontinued, all six monkeys showed after twelve hours, behavioral and
physiological changes described by the researchers as mild abstinence signs. Two of the
six monkeys then initiated and maintained for several weeks the self-administration of
THC.

The investigators believe these findings are evidence for mild psychological and
physiological dependence on THC. However, vehicle controls were not included in the
research design. Thus, the abstinence signs and subsequent behavior may possibly be
accounted for by the biological effects in of the Tween vehicle.

Harris et al. (1972) utilized several procedures to maximize the possible conditions
necessary for developing self-injection in monkeys. These procedures included: spontaneous
Delta 9 THC self administration with no previous training to the technique;
self-administration of A‘ THC after training, with cocaine alone and a mixture of cocaine
and Delta 9 THC. Doses utilized ranged from 20 to 500 micrograms per kilogram suspended in
polyvinylpyrrolidone. In all cases, monkeys failed to self -administer Delta 9 THC.

The researchers conclude that A‘ THC lacks the reinforcing effects of psychomotor
stimulants and depressants which monkeys readily self infuse with no auxiliary incentives.
Also Delta 9 THC lacks a reinforcing function even for monkeys that are well-trained with
cocaine and have experienced several days of rather large quantities of Delta 9 THC during
the early pleases of extinction of the cocaine reinforced response.

Finally, the results demonstrate that a two week period of exposure to Al THC (in a
mixed solution with cocaine) does not result in the degree of homeostatic imbalance which
occurs with morphine, ethanol, barbiturates and sometimes the amphetamines which accounts
for the continued self-administration of these drugs.


 

 














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