Pot's Social Dangers Unknown, Say Researchers

Little Evidence That Marijuana Causes Behavioral Problems, Study Shows

From the WebMD Archives

May 17, 2004 -- You've probably seen the commercial: an egg frying in a pan. It's not breakfast being served but a strong warning about the dangers of recreational drug use: "This is your brain. This is your brain on drugs. Any questions?"

Yes, say British researchers. Can you prove it?

After reviewing 48 previous studies from around the globe -- including 16 they deem of higher quality and involving more than 81,000 young people -- the University of Birmingham scientists conclude that the much-touted dangers resulting from marijuana may be overstated.

"The evidence that cannabis use in itself causes psychological and social problems is not strong," lead researcher John Macleod, MRCGP, PhD, tells WebMD. "This does not mean that cannabis is harmless, it means the evidence is weak."

Macleod's research only included studies investigating behavior issues among teens and children, not pot-smoking effects on physical health.

Macleod says the data clearly show that teens who smoke pot are also more likely to display psychological and social problems such as poor school performance, violent and antisocial behavior, and a tendency to use other drugs. But his new report in The Lancet indicates there's little proof that marijuana is the reason why.

In other words, children and teens with problem behavior may be more inclined to smoke pot but there's little to suggest it makes them become problem kids. "We need better research to clarify whether cannabis use causes problems or is merely a marker of problems caused by other things," Macleod explains.

He says that previous studies suggesting marijuana caused behavioral problems were often flawed -- showing bias in the selection of study participants, little consideration for other factors that could skew the result of studies, or relying too much on uncorroborated, self-reported surveys.

Relaxed Laws Elsewhere

Igor Grant, MD, a psychiatrist and noted marijuana researcher at the University of California, San Diego School of Medicine, says he is not especially surprised by Macleod's findings. Last year, he did his own review of previous research on how marijuana use affects thinking and other neurological abilities, and found even long-term and daily use causes little permanent brain damage in adults (his data did not involve children). Grant was not involved in Macleod's research.

"What this paper does is put things more into perspective, but that doesn't mean that marijuana is not harmful," Grant tells WebMD. "We need to separate between the effects drugs may have on a child versus an adult. It could be that certain substances that are not harmful in adults may have harmful effects in kids. But overall, these researchers are finding what others are finding anecdotally in Europe and elsewhere."

Macleod's research -- funded by the United Kingdom Department of Health -- comes just after the British government relaxed its marijuana possession laws, and it's already been decriminalized in Spain, Italy, Portugal, the Netherlands, and Belgium. Canada is also considering decriminalization for amounts less than a half-ounce, and this fall, pharmacies in British Columbia will begin selling marijuana for medicinal purposes -- without a prescription -- under a national health service plan.

In the U.S., where some 700,000 arrests are made each year for marijuana use and possession, the debate on its impact continues.

Two weeks ago, federal health officials reported in The Journal of the American Medical Association that over the past decade, more American adults have abused or become dependent on pot even though overall use rates have remained steady. "The resultsof this study underscore the need to develop and implement newprevention and intervention programs targeted at youth, particularlyminority youth," write researchers from the National Institutes of Health.

That same week, another study in the American Journal of Public Health reported that neither the severity nor leniency of current marijuana laws seems to influence whether experienced users continue to smoke pot.

States vs. Feds

Other countries have decriminalized marijuana largely because studies show that its use can reduce chronic pain, nausea, and muscle spasms and lower rising eye pressure that causes glaucoma. Marijuana has been used -- legally or not -- to treat some 30 conditions, including AIDS, multiple sclerosis, and cancer. In fact, until the 1930s, marijuana was legally available in the U.S. as a medicinal treatment.

Nine U.S. states have laws allowing for the use of medical marijuana under a doctor's recommendation -- Alaska, Arizona, California, Colorado, Hawaii, Maine, Nevada, Oregon, and Washington. But the Justice Department contends that federal drug laws that make its use and possession illegal take precedent over state laws.

Last month, officials from two state medical boards were accused by a House Criminal Justice subcommittee of ignoring federal drug laws in favor of their state's statutes by allowing doctors to promote the use of marijuana for medicinal purposes, despite a potential for abuse.

Weeks later, a judge ruled that federal prosecutions of medical marijuana users in permitting states are unconstitutional if the pot isn't sold, transported across state lines, or used for non-medicinal purposes. The judge ordered the federal government to stop prosecuting a sick California woman smoking pot under doctor's orders, and not to raid or prosecute a group in that state -- where medical marijuana use is allowed -- that grows and distributes it to patients.

Show Sources

SOURCES: John Macleod, MRCGP, PhD, primary care physician and epidemiologist, University of Birmingham, England. Igor Grant, MD, professor of psychiatry, University of California, San Diego School of Medicine; director, UCSD Center for Medicinal Cannabis Research Center. Macleod, J. The Lancet, May 15, 2004; vol 363: pp 1579-1588. Compton, W. TheJournal of the American Medial Association, May 5, 2004; vol 291: pp 2114-2121. Reinarman, C. American Journal of Public Health, May 2004; vol94: pp 836-842. WebMD Medical News: "States Defend Medical Marijuana Policies." Associated Press. Grant, I. Journal of the International Neuropsychological Society, July 2003.
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