Heavy Marijuana Use Doesn't Damage Brain

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.

"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.