It is now generally accepted that "...except for the
harms associated with smoking, the adverse effects of marijuana
use are within the range of effects tolerated for other medications"
(Institute of Medicine Report of 1999). This opinion is supported
by recent clinical research. Besides abuse and dependency,
the main side effects of concern are those on the cardiovascular,
immune, and hormonal systems, and on cognitive functions.
Research has shown that cannabis produces acute side effects
that are within the range of side effects tolerated for other
medicinal drugs. Acute side effects relate mainly to psychological
effects (cognitive impairment, altered perception) and circulation
(decrease of blood pressure). New research adds to the evidence
of cannabis’s interaction with other medicinal drugs,
effects on cognitive function, and increased risk of heart
In an anonymous survey of 128 patients in Germany, Switzerland,
and Austria on the medical use of dronabinol and natural cannabis
products, 71% reported no side effects (Schnelle et al. 1999).
26% reported moderate and 3% severe effects. The overall judgment
of "no side effects" was also given in some cases
where certain side effects (e.g. dry mouth or anxiety) were
experienced but apparently regarded as minor by the subjects.
The first U.S. study using marijuana for people with HIV
has found that smoking the plant does not disrupt the effect
of antiretroviral drugs that keep the virus in check (Ksel
et al. 2002). Kosel and colleagues of San Francisco General
Hospital were limited to focusing on marijuana's safety rather
than its effectiveness. The 67 people who participated in
the study were kept in the hospital during the 21-day study
period. Researchers were especially interested in studying
people on drug regimes that contain protease inhibitors, because
THC is metabolised by the same system in the liver as those
drugs. Subjects on stable regimens involving taking Indinavir
800 mg every 8 h (n = 28) or Nelfinavir 750 mg three time
a day (n = 34) were randomized to one of three treatment arms:
3.95% THC marijuana cigarettes, dronabinol 2.5 mg capsules,
or placebo capsules administered three times daily. Serial
blood sampling was performed at baseline and on day 14 of
treatment. In all groups the level of virus in the blood dropped
or remained undetectable by current tests. There was no statistically
significant difference among the three groups, with those
taking THC or marijuana having slightly lower levels. With
regard to the pharmacokientic data, the authors stated:
"Despite a statistically significant decrease in C(max)
of IDV in the marijuana arm, the magnitude of changes in IDV
and NFV pharmacokinetic parameters in the marijuana arm are
likely to have no short-term clinical consequence. The use
of marijuana or dronabinol is unlikely to impact antiretroviral
efficacy" (Kosel et al. 2002)
Lead researcher Donald Abrahms concluded:
"Controlled clinical trials investigating smoked marijuana
can be safely conducted. Neither smoked nor oral cannabinoids
have an adverse effect on HIV RNA levels, immune parameters
or protease inhibitor kinetics over a 21 day treatment period
in patients with HIV infection on a stable antiretroviral
therapy regimen. Use of both smoked marijuana and dronabinol
lead to increased weight gain compared to placebo. Further
studies to investigate the therapeutic potential of smoked
marijuana and other cannabinoids are warranted.” (Abrahms
et al, 2002)
Although the ability to perform complex cognitive operations
is assumed to be impaired following acute marijuana smoking,
complex cognitive performance after acute marijuana use has
not been adequately assessed under experimental conditions.
In a study by Hart et al. (2001) an inter-participant double-blind
design was used to evaluate the effects of acute marijuana
smoking on complex cognitive performance in experienced marijuana
smokers. Acute marijuana smoking produced only minimal effects
on complex cognitive task performance:
"Eighteen healthy research volunteers (8 females, 10
males), averaging 24 marijuana cigarettes per week, completed
this three-session outpatient study; sessions were separated
by at least 72-hrs. During sessions, participants completed
baseline computerized cognitive tasks, smoked a single marijuana
cigarette (0%, 1.8%, or 3.9% Delta(9)-THC w/w), and completed
additional cognitive tasks. Blood pressure, heart rate, and
subjective effects were also assessed throughout sessions.
Marijuana cigarettes were administered in a double-blind fashion
and the sequence of Delta(9)-THC concentration order was balanced
across participants. Although marijuana significantly increased
the number of premature responses and the time participants
required to complete several tasks, it had no effect on accuracy
on measures of cognitive flexibility, mental calculation,
and reasoning. Additionally, heart rate and several subjective-effect
ratings (e.g., "Good Drug Effect," "High,"
"Mellow") were significantly increased in a Delta(9)-THC
concentration-dependent manner. These data demonstrate that
acute marijuana smoking produced minimal effects on complex
cognitive task performance in experienced marijuana users"
(Hart et al. 2001).
Moderate smoking of cannabis increases the risk of a heart
attack for middle-aged and elderly users during the first
hour after using the drug, a study published in 2001 says
(Mittleman et al. 2001). A small portion (0.2%) of patients
suffering from a heart attack had smoked cannabis shortly
before symptoms began. Cannabis has an influence on blood
pressure and heart rate. This may be of relevance for people
with coronary heart disease, as are several other drugs that
influence circulation. Of the 3882 patients suffering a heart
attack, 124 reported smoking marijuana in the previous year,
among them 9 within 1 hour of heart attack symptoms. The risk
of heart attack onset was significantly elevated 4.8 times
over baseline (95% confidence interval: 2.4-9.5) in the first
hour after cannabis use. In the second hour it was 1.7 times
greater, and returned to baseline afterwards. Murray Mittleman,
a professor at Harvard Medical School and director of cardiovascular
epidemiology at Beth Israel-Deaconess Medical Centre, and
his colleagues wrote in their publication that smoking marijuana
is "a rare trigger of acute myocardial infarction".
He noted that cannabis was about as risky as taking a walk
for an active person with heart disease, or as sex for a patient
with sedentary life style.
Much research has been conducted to address the question
of driving ability under the influence of the drug. For example,
a major recent study by the UK Transport Research Laboratory
found that one single glass of wine impairs driving ability
more than smoking a cannabis cigarette (New Scientist of 19
March 2002). The study also found that drivers on cannabis
tended to be aware of their intoxicated state, and drove more
cautiously to compensate their impairment. This is in good
agreement with earlier research of recent years (reviews:
Smiley 1999, Chesher & Longo 2002). Another study investigated
the effects of chronic exposure to cannabis on the effects
of alcohol on driving-related psychomotor skills. Chronic
cannabis use (in the absence of acute administration) did
not potentiate the effects of alcohol. In fact, the regular
users showed lower scores for dizziness and a superior tracking
accuracy compared to infrequent users after they consumed
alcohol (Wright & Terry 2002).
Abrams DI, et al. Short-Term Effects of Cannabinoids In Patients
With HIV Infection. J Cannabis Ther 2002;2(2):92-93.
Chesher G, Longo M. Cannabis and Alcohol in Motor Vehicle
Accidents. In: In: Grotenhermen F, Russo E, editors. Cannabis
and cannabinoids. Pharmacology, toxicology, and therapeutic
potential. Binghamton (NY): Haworth Press, 2002: 101-110.
Fried P, Watkinson B, James D, Gray R. Current and former
marijuana use: preliminary findings of a longitudinal study
of effects on IQ in young adults. CMAJ 2002;166(7):887-91
Hart CL, van Gorp W, Haney M, Foltin RW, Fischman MW. Effects
of acute smoked marijuana on complex cognitive performance.
Mittleman MA, Lewis RA, Maclure M, Sherwood JB, Muller JE.
Triggering myocardial infarction by marijuana. Circulation
Schnelle M, Grotenhermen F, Reif M, Gorter RW. Ergebnisse
einer standardisierten Umfrage zur medizinischen Verwendung
von Cannabisprodukten im deutschen Sprachraum, [Results of
a standardized survey on the medical use of cannabis products
in the German-speaking area]. Research in Complementary Medicine
1999;(Suppl 3) 28-36.
Smiley AM: Marijuana: on road and driving simulator studies.
In: Kalant H, Corrigal W, Hall W, Smart R, eds. The Health
Effects of Cannabis. Toronto: Addiction Research Foundation,
Wright A, Terry P. Modulation of the effects of alcohol on
driving-related psychomotor skills by chronic exposure to
cannabis. Psychopharmacology (Berl) 2002;160(2):213-9.