Adverse Health Effects of Marijuana Use

Nora D. Volkow, M.D., Ruben D. Baler, Ph.D., Wilson M. Compton, M.D., and Susan R.B.
Weiss, Ph.D.

In light of the rapidly shifting landscape regarding the legalization of marijuana for
medical and recreational purposes, patients may be more likely to ask physicians about its
potential adverse and beneficial effects on health. The popular notion seems to be that
marijuana is a harmless pleasure, access to which should not be regulated or considered
illegal. Currently, marijuana is the most commonly used “illicit” drug in the United States,
with about 12% of people 12 years of age or older reporting use in the past year and
particularly high rates of use among young people. The most common route of administration
is inhalation. The greenish-gray shredded leaves and flowers of the Cannabis sativa plant are
smoked (along with stems and seeds) in cigarettes, cigars, pipes, water pipes, or “blunts”
(marijuana rolled in the tobacco-leaf wrapper from a cigar). Hashish is a related product
created from the resin of marijuana flowers and is usually smoked (by itself or in a mixture
with tobacco) but can be ingested orally. Marijuana can also be used to brew tea, and its oil-
based extract can be mixed into food products.

There is also a need to improve our understanding of how to harness the potential
medical benefits of the marijuana plant without exposing people who are sick to its intrinsic
risks. The authoritative report by the Institute of Medicine, Marijuana and
Medicine, acknowledges the potential benefits of smoking marijuana in stimulating appetite,
particularly in patients with the acquired immunodeficiency syndrome (AIDS) and the related
wasting syndrome, and in combating chemotherapy-induced nausea and vomiting, severe
pain, and some forms of spasticity. The report also indicates that there is some evidence for
the benefit of using marijuana to decrease intraocular pressure in the treatment of glaucoma.
Nonetheless, the report stresses the importance of focusing research efforts on the therapeutic
potential of synthetic or pharmaceutically pure cannabinoids.Some physicians continue to
prescribe marijuana for medicinal purposes despite limited evidence of a benefit (see box).
This practice raises particular concerns with regard to long-term use by vulnerable
populations. For example, there is some evidence to suggest that in patients with symptoms
of human immunodeficiency virus (HIV) infection or AIDS, marijuana use may actually
exacerbate HIV-associated cognitive deficits.75 Similarly, more research is needed to
understand the potential effects of marijuana use on age-related cognitive decline in general
and on memory impairment in particular.

Research is needed on the ways in which government policies on marijuana affect

public health outcomes. Our understanding of the effects of policy on market forces is quite
limited (e.g., the allure of new tax-revenue streams from the legal sale of marijuana, pricing
wars, youth-targeted advertising, and the emergence of cannabis-based medicines approved
by the Food and Drug Administration), as is our understanding of the interrelated variables of
perceptions about use, types of use, and outcomes. Historically, there has been an inverse
correlation between marijuana use and the perception of its risks among adolescents .

CONCLUSIONS

Marijuana use has been associated with substantial adverse effects, some of which have been
determined with a high level of confidence . Marijuana, like other drugs of abuse, can result
in addiction. During intoxication, marijuana can interfere with cognitive function (e.g.,
memory and perception of time) and motor function (e.g., coordination), and these effects can
have detrimental consequences (e.g., motor-vehicle accidents). Repeated marijuana use
during adolescence may result in long-lasting canges in brain function that can jeopardize
educational, professional, and social achievements. However, the effects of a drug (legal or
illegal) on individual health are determined not only by its pharmacologic properties but also
by its availability and social acceptability. In this respect, legal drugs (alcohol and tobacco)
offer a sobering perspective, accounting for the greatest burden of disease associated with
drugs77 not because they are more dangerous than illegal drugs but because their legal status
allows for more widespread exposure. As policy shifts toward legalization of marijuana, it is
reasonable and probably prudent to hypothesize that its use will increase and that, by
extension, so will the number of persons for whom there will be negative health
consequences.
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