Regular marijuana use bad for teens' brains

Frequent marijuana use can have a significant negative effect on the brains of teenagers and young adults, including cognitive decline, poor attention and memory, and decreased IQ, according to new research.
"It needs to be emphasised that regular cannabis use, which we consider once a week, 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.
People who have become addicted to marijuana can lose an average of six IQ points by adulthood, according to Lisdahl, referring to a 2012 longitudinal study of 1,037 participants who were followed from birth to age 38.

Brain imaging studies of regular marijuana users have shown significant changes in their brain structure, particularly among adolescents, Lisdahl said.
Abnormalities in the brain's gray matter, which is associated with intelligence, have been found in 16- to 19-year-olds who increased their marijuana use in the past year, she said.
These findings remained even after researchers controlled for major medical conditions, prenatal drug exposure, developmental delays and learning disabilities, she added.

Tetrahydrocannabinol, or THC, is responsible for most of marijuana's psychological effects, researchers said.
Some research has shown that frequent use of high potency THC can increase risk of acute and future problems with depression, anxiety and psychosis.

"Recent studies suggest that this relationship between marijuana and mental illness may be moderated by how often marijuana is used and potency of the substance," Alan Budney, of Dartmouth College said.
"Unfortunately, much of what we know from earlier research is based on smoking marijuana with much lower doses of THC than are commonly used today," Budney said.
The research was presented at the American Psychological Association's Annual Convention.