Marijuana use shrinks teenagers' brains: Experts

Frequent marijuana use among teenagers can lead to cognitive decline, poor attention and memory and decreased intelligence quotient (IQ), psychologists warn.

Abnormalities in the brain's grey matter, which is associated with intelligence, have been found in 16- to 19-year-olds who increased their marijuana use.

"It needs to be emphasised that regular cannabis use is not safe and may result in addiction and neurocognitive damage, especially in youth," said Krista Lisdahl, director of the brain imaging and neuropsychology lab at University of Wisconsin-Milwaukee.

Brain imaging studies of regular marijuana users have shown significant changes in their brain structure, particularly among adolescents, Lisdahl added.

People who have become addicted to marijuana can lose an average of six IQ points by adulthood.

Countries must consider regulating levels of tetrahydrocannabinol (THC) - the major psychoactive chemical in marijuana - in order to reduce potential neurocognitive effects, researchers emphasised.

THC is responsible for most of marijuana's psychological effects.

Previous research has shown that frequent use of high potency THC can increase risk of acute and future problems with depression, anxiety and psychosis.

"This relationship between marijuana and mental illness may be moderated by how often marijuana is used and potency of the substance," claimed Alan Budney from Dartmouth College in the US.

The psychologists discussed public health implications of marijuana at the American Psychological Association's 122nd annual convention this week.