Under-Age Pot Use

Marijuana use at an early age could drop a few IQ points that will never return

(RxWiki News) Marijuana can stunt brain development in minors. Frequent marijuana use, starting at a young age, can lower a person’s IQ up to five points over the years.

A recent study followed 1,037 people’s marijuana use from the age of 13 to 38. Results found that people who use marijuana while their brain is still developing can stunt their smarts.

"Pot use by minors is illegal for a good reason."

Madeline H. Meier, PhD, postdoctoral associate at the Center for Child and Family Policy at Duke University, led an investigation into how early use of marijuana can affect psychological development.

This study followed 1,037 people born in 1972/1973 to the age of 38. Researchers monitored marijuana use and neuropsychological development in each participant from the age of 13 to 38.

None of the participants began using marijuana before they were first evaluated at age 13. Their marijuana use was assessed at ages 18, 21, 26, 32 and 38.

Only the group of people who never used marijuana showed an increase in their intelligence quotient (IQ). Taken when they were in the age range of 7-13 then again at 38, never users’ IQ went up nearly a point.

The rest of the group that used marijuana showed a greater decline in IQ for more frequent marijuana use.

Occasional users showed a decline of nearly one IQ point, regular users showed a decline of around three points and heavy users showed a decline of around five IQ points.

Researchers said participants who started using marijuana before the age of 18 showed greater IQ decline than those who started using marijuana after the age of 18.

More extensive cognitive tests were also taken to gauge memory, visual and verbal processing and reasoning. Decline in these areas was consistent with IQ decline in marijuana users.

Researchers determined that stopping the use of marijuana after adolescent onset use did not reverse the effects of marijuana on neuropsychological functioning.

Study authors recommend that their findings showed good reason for putting policies in place to prohibit adolescent access to marijuana.

This study will be published in August in the Proceedings of the National Academy of Sciences of the United States of America Early Edition. Funding for this study was provided by the UK Medical Research Council Grants, US National Institute(s) on Aging; Mental Health; and Drug Abuse, and the Jacobs Foundation. No conflicts of interest were reported.

Review Date: 
August 22, 2012