Study finds no long-term negative cognitive effects from marijuana

From Raw Story By Eric W. Dolan
Wednesday, July 11, 2012

While cognitive performance is negatively affected by cannabis use, the negative effects appear to completely wear off within a month, according to research published in the Experimental and Clinical Psychopharmacology in late June.

“With the number of cannabis users both illicitly and licitly increasing, the question of any potential lasting impact from cannabis use is increasingly important,” Amy M. Schreiner and Michael E. Dunn of the University of Central Florida wrote in their study.

Numerous studies have found that cannabis use affects memory, attention, perceptual-motor tasks, and other cognitive processes, but studies on how long these effects last has been inconsistent. The studies were complicated by the fact that psychoactive compounds in marijuana can linger in the body for days.

In hopes of better understanding the long-term, lasting effects of cannabis use, the researchers used a meta-analysis, a statistical procedure that allows researchers to mathematically summarize the results of a number of different studies.

Schreiner and Dunn’s study included two of these meta-analyses. The first was comprised of 33 studies that examined the cognitive effects of cannabis use after intoxication had worn off. The second was comprised of 13 studies that also examined the cognitive effects of cannabis use after intoxication had worn off, but this group of studies tested users after at least 25 days of abstinence.

The study found that cannabis use caused small impairments in attention, learning, and other cognitive processes that persisted after intoxication. However, the researchers said it was unclear if these minor impairments “translate[d] into practical impairments in functioning.” But the second meta-analysis suggested that these minor impairments don’t last longer than a month.

“While the first meta-analysis revealed a small significant negative effect for general performance and a number of cognitive domains, the clinical significance remains unclear,” Schreiner and Dunn explained. “A second meta-analysis focusing on studies with longer abstention periods was conducted and indicated no lasting residual effects on neurocognitive performance as a result of cannabis use… Whether differences seen in the initial days or weeks of abstinence are due to drug residue effects or withdrawal effects, after approximately 1 month these effects do not persist for the moderate to heavy user.”

Study: Heavy Marijuana Use Doesn’t Damage Brain

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Analysis of Studies Finds Little Effect From Long-Term Use

By Sid Kirchheimer WebMD Medical News

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.

Surprising Finding

“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.”

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 diseases.

“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 users.”

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.

‘Highly Effective Medicine’

“I just re-published a paper of the first survey for marijuana toxicity done in 1863 by the British government in India that was the most exhaustive medical study of its time in regards to possible difficulties and toxicity of cannabis. And it reached the same conclusion as Grant,” Mikuriya tells WebMD.

“This is merely confirming what was known over 100 years ago, as well as what was learned by various government findings doing similar research — marijuana is not toxic, but it is a highly effective medicine.”

In fact, marijuana was available as a medicinal treatment in the U.S. until the 1930s.

Lester Grinspoon, MD, a retired Harvard Medical School psychiatrist who studied medicinal marijuana use since the 1960s and wrote two books on the topic, says that while Grant’s finding provides more evidence on its safety, “it’s nothing that those of us who have been studying this haven’t known for a very long time.

“Marijuana is a remarkably safe and non-toxic drug that can effectively treat about 30 different conditions,” he tells WebMD. “I predict it will become the aspirin of the 21st century, as more people recognize this.”