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Major Studies of Drugs and Drug Policy | ||||
Canadian Senate Special Committee on Illegal Drugs | ||||
Volume I - General Orientation |
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Chapter 7 - Cannabis: Effects and ConsequencesAcute effects of cannabis
In
toxicology, acute effects are those that are produced immediately after use and
while the psychoactive effects are being experienced. These effects also
correspond to what has been called cannabis intoxication ever since Moreau de
Tours in 1845.[1][17] The “real”
effects – on biological systems – and the effects experienced by users can vary
based on a set of factors, such as the user’s experience with cannabis and
other drugs (including tobacco), the user’s expectations and the context of
use. In fact, [translation] “the
psychoactive effects of cannabis, more than any other substance, vary from one
subject to another and, for the same subject, from one experience to another.”[2][18]
Additionally, with no reliable method to measure THC content in plasma, it is
difficult to link the duration and strength of effects to the various cannabis
preparations, in particular because of variations in the composition of the
substance and in the bioavailability of THC. It is even more difficult to
attribute relatively rare effects (for example, the appearance of psychotic
symptoms) insofar as it is hard to decide if the co-occurrence is coincidental,
if these effects stem from other substances often associated with cannabis use
or from very high doses of cannabis, or from interactions between these various
factors.[3][19] The
acute effects of cannabis are relatively well documented. Research sometimes
distinguishes between central and peripheral effects[4][20], sometimes
between somatic effects and psychological or psychomotor effects[5][21], and
sometimes is simply content to list the effects of one type or another.[6][22] Cannabis
intoxication is generally considered to consist of two main phases:
More
specifically, depending on their type of action, a distinction is made between
truly somatic effects and more psychological ones.
Somatic,
cognitive and psychomotor effects are related to the amount of cannabis
inhaled and the concentration of THC. Thus, according to INSERM: A quantity that corresponds to 25 puffs impairs
psychomotor skills and cognitive performance, and more markedly than
consumption of 10 puffs or 4 puffs. Maximum plasma levels then rise from 57
ng/ml (for 4 puffs from a cigarette containing 1.75% D9THC) to 268
ng/ml (for 25 puffs from a cigarette containing 3.55% D9THC). Heishman et al. (1997) established
an approximate equivalence between 16 puffs at 3.55 % D9THC and
approximately 70g of alcohol. At these levels, memory, cognitive and
psychomotor performance and mood are impaired. [9][25]
[translation] The
cognitive and psychomotor effects may continue for more than five hours, and
some cognitive impairment may extend for 24 hours. At high doses, or with inexperienced users, cannabis
may cause a certain number of negative reactions that can even include a
genuine paranoid, hallucinatory, manic or hypomanic psychotic experience.
However these experiences are brief. Some disorders documented with high doses
include:
These
phenomena are relatively rare (less than 1 in a thousand psychiatric
admissions). Primarily, it is difficult to establish that cannabis was the
cause. In fact, in most cases, the most likely hypothesis is that these
subjects were already predisposed, or had even already had psychotic or
schizophrenic experiences. Use of other substances, alcohol, other illicit
drugs, or medications, could also play an important role. The link between cannabis use and psychosis is a
very controversial issue. At the moment, we lack a corpus of comparable,
methodologically sound studies repeatedly yielding similar conclusions. The
results of existing studies are often complex or ambiguous and the personal
opinions of the researchers often interfere with the interpretations. Further
deepening our scientific knowledge is still necessary. However, there is
extensive, albeit incomplete, consensus on the ability of heavy cannabis
consumption or intoxication to induce an acute transitory psychotic state in
healthy subjects. The frequency of this condition is unknown and the mechanisms
are hypothetical. [10][26] In
accordance with the collective expertise of INSERM, we can establish the
following: The psychotic disorders caused by cannabis use are
brief psychotic episodes that last less than two months, even four months[sic],
sometimes a week. The premorbid personality does not present a pathological
aspect. Regular users are at greater risk than occasional users. Onset is
abrupt, in two or three days, with or without a recent increase in the use of
toxic agents, sometimes with a psychological or somatic precipitating factor.
Some symptoms appear more specific: behavioural problems, aggression, visual
hallucinations, polymorphic nature of the delirium along various themes,
psychomotor disinhibition. (…) Compared to a schizophrenic disorder, subjects
are younger, 20 to 30 years of age rather than 25 to 30, with a greater
proportion of poorly socialized males. [11][27]
[translation] However,
here too, the data are relatively contradictory and, according to professor
Roques, there is support for the belief that usage is more widespread among
people with previous mental disorders.[12][28] [1][17] Moreau de Tours, J., Du haschich ou de l’aliénation mentale, étude psychologique. Paris: Masson. [2][18] INSERM, op. cit., page 118. [3][19] See WHO, 1997, op. cit., 3. [4][20] For example, this is the case with the
classification proposed by Ben Amar (at press). [5][21] This is the case with the collective expertise
of INSERM (2001). [6][22] This is the case with most works: WHO, 1997;
Swiss Federal Commission for Drug Issues (1999) Rapport sur le cannabis. Berne: Swiss Federal Office of Public
Health; and the report by Wheelock (2002). [7][23]
Fant, R.V. et al. (1998) “Acute and residual effects of marijuana
in humans.” Pharmacology, Biochemistry
and Behavior, 60: 777-784. [8][24] Roques, B. (1999) La dangerosité des drogues. Paris: Odile Jacob, page: 184. [9][25]
INSERM, op. cit., page: 203. [10][26] Hanak,
C. et al. (2002) “Cannabis, mental health and dependence.” in Pelc, I.
(ed.), International Scientific
Conference on Cannabis, Brussels. [11][27] INSERM, op.
cit., page 124. [12][28] Roques, B., op. cit., page 186. |