New study finds heavy marijuana use harms brain

Frequent marijuana use has a powerful impact on the human brain's intellectual functions, particularly among people who start using it while young, scientists have found.

Researchers report that heavy marijuana use is linked to adverse changes in key brain regions -- those associated with reward, decision-making and motivation. Heavy marijuana use was described as four times a week for at least six months, according to a report in the Proceedings of the National Academy of Sciences.

The analysis, which adds to a growing body of medical literature on how marijuana harms the brain, comes on the heels of sociological studies reported in recent months showing that teens who are regular users are 60 percent less likely to finish high school.

A key finding of the new study was a lower IQ among chronic users, a similar finding to earlier research, which underlined as much as an eight-point IQ loss.

"Marijuana is the fastest rising drug among teenagers and there is a decreasing perception that it's harmful," said Dr. Scott Krakower, a specialist in child and adolescent psychiatry with the North Shore-Long Island Jewish Health System.

"Parents also don't recognize that marijuana is harmful or realize that it's a gateway to other drugs," Krakower said.

Researchers at the University of Texas conducted the new study and used magnetic resonance imaging to view key brain regions in heavy users. Among their discoveries, chronic marijuana users have a smaller brain volume in the orbitofrontal cortex, a part of the brain commonly associated with addiction.

Despite that, the MRI studies of the 48 marijuana users revealed they had enhanced areas in other parts of the brain, suggesting that the three-pound organ attempts to compensate for its loss.

"We have seen a steady increase in the incidence of marijuana use since 2007," said Dr. Francesca Filbey, an associate professor at the University of Texas.

"However, research on [marijuana's] long-term effects remains scarce despite the changes in legislation surrounding marijuana," Filbey said.

Paul Armentano, deputy director of NORML, a Washington, D.C.-based advocacy organization supporting the legalization of responsible pot use by adults, said the study is flawed.

"Investigators cannot determine whether these differences are caused by the subject's cannabis use, whether these differences existed prior to subjects' ever trying cannabis, or whether these differences persist when users' cannabis consumption ceases," Armentano said.

Krakower, however, said the new research corroborates other recent studies. While pot is helpful in pain control, he said, more research is needed to understand its global impact on the brain.

Also unanswered, Krakower added, is how current high-potency varieties of the plant are influencing brain development in young users.

In recent years, he said, the amount of tetrahydrocannabinol, or THC, the principal psychoactive component in marijuana plants, has increased in pot sold on Long Island and beyond.

"Some THC levels [are] as high as 90 percent," he said.