Casual marijuana use may alter brain shape and function in young adults

A new study on the effects of marijuana smoking on the brains of young people raises new questions about risks of casual drug use. MRI images showed pot smoking affected the size and shape of areas of the brain that are known to play an important role in emotion, motivation and decision making. Marijuana is the most commonly used drug in the U.S., and part of the reason for its popularity is its perception as mostly harmless -- its side effects, like increased hunger or forgetfulness, minimal and short-lived. But previous studies have shown marijuana use to have detrimental effects on motivation, attention, learning, and memory impairments. This new study lends credence to neurologists and public health officials who've previously suggested even casual pot smoking -- a joint or two per week -- might effect brain function and formation in young adults. "This study suggests that even light to moderate recreational marijuana use can cause changes in brain anatomy," explained Carl Lupica, a drug addiction researcher at the National Institute on Drug Abuse, but who did not participate in this latest research effort. "These observations are particularly interesting because previous studies have focused primarily on the brains of heavy marijuana smokers, and have largely ignored the brains of casual users," Lupica added. Published this week in The Journal of Neuroscience, the study details the work of researchers Jodi Gilman, Anne Blood and Hans Breiter. The scientists, who conducted their work at Massachusetts General Hospital, used MRI imaging to study the brains of 18- to 25-year olds, comparing those who reported casual marijuana use and those that did not. They found more frequent smoking habits were associated with abnormalities in the nucleus accumbens and amygdala -- areas of the brain that affect emotion and motivation.