Heavy Marijuana Use Doesn't Damage Brain
Analysis of Studies Finds Little Effect From Long-Term Use
WebMD News Archive
July 1, 2003 -- Long-term and even daily marijuana use doesn't appear to
cause permanent brain damage, adding to
evidence that it can be a safe and effective treatment for a wide range of
diseases, say researchers.
The researchers found only a "very small" impairment in memory
and learning among long-term marijuana users. Otherwise, scores on thinking
tests were similar to those who don't smoke marijuana, according to a new
analysis of 15 previous studies.
In those studies, some 700 regular marijuana users were
compared with 484 non-users on various aspects of brain function -- including
reaction time, language and motor skills, reasoning ability, memory, and the
ability to learn new information.
"We were somewhat surprised by our finding, especially since
there's been a controversy for some years on whether long-term cannabis use
causes brain damage," says lead researcher and psychiatrist Igor Grant, MD.
"I suppose we expected to see some differences in people who
were heavy users, but in fact the differences were very minimal."
The marijuana users in those 15 studies -- which lasted between
three months to more than 13 years -- had smoked marijuana several times a week
or month or daily. Still, researchers say impairments were less than what is
typically found from using alcohol or other drugs.
"All study participants were adults," says Grant, professor of
psychiatry and director of the Center for Medicinal Cannabis Research Center at
the University of California, San Diego School of Medicine.
"However, there might be a different set of circumstances to a
12-year-old whose nervous system is still developing."
10 States OK Marijuana Use
Grant's analysis, published in the July issue of the Journal
of the International Neuropsychological Society, comes as many states
consider laws allowing marijuana to be used to treat certain medical
conditions. Earlier this year, Maryland became the 10th state to
allow marijuana use to relieve pain and other symptoms of AIDS, multiple sclerosis, cancer,
glaucoma, and other conditions -- joining Alaska, Arizona, California,
Colorado, Hawaii, Maine, Nevada, Oregon, and Washington.
Medicinal marijuana is available by prescription in the
Netherlands and a new marijuana drug is expected to be released in Great
Britain later this year. In the U.S. and elsewhere, Marinol, a drug that is a
synthetic form of marijuana and contains its active ingredient, THC, is
available by prescription to treat loss of appetite associated with weight loss
in AIDS patients.
Grant says he did the analysis to help determine long-term
toxicity from long-term and frequent marijuana use. His center is currently
conducting 11 studies to determine its safety and efficacy in treating several
"This finding enables us to see a marginal level of safety, if
those studies prove that cannabis can be effective," Grant tells WebMD. "If we
barely find this effect in long-term heavy users, then we are unlikely to see
deleterious side effects in individuals who receive cannabis for a short time
in a medical setting, which would be safer than what is practiced by street
Grant's findings come as no surprise to Tod Mikuriya, MD,
former director of non-classified marijuana research for the National Institute
of Mental Health Center for Narcotics and Drug Abuse Studies and author of
The Marijuana Medical Handbook: A Guide to Therapeutic Use. He is
currently president of the California Cannabis Medical Group, which has treated
some 20,000 patients with medicinal marijuana and Marinol.