Teens who drink alcohol are more likely to damage brain tissue than those who use marijuana, a new study shows.

Researchers at UC San Diego followed 92 adolescents between the ages of 16 and 20 for 18 months. During that time, half of the teens — who already had substantial histories of alcohol and marijuana intake — continued to use the substances in varying amounts. The other half abstained or consumed very little, just as they had before.

The before and after scans of teens who had five or more drinks per week showed a reduction in the health of white matter brain tissue, which could mean damage to memory, attention and decision-making abilities. The frequency of pot use — some participants smoked it as many as nine times a week during the study period — did not show a change in brain tissue health.

— Posted by Alexander Reed Kelly.

The Huffington Post:

The researchers are not sure why alcohol had an effect and marijuana did not. They said the study results cannot be considered definitive without more research. They also said they do not know if the reduced brain tissue health is permanent.

Because the researchers followed the subjects for 18 months, they were able to at least partially monitor preexisting differences in the two groups. But Jacobus conceded that eliminating other factors — such as genetics, home environment, and even minimal use of other drugs — is very difficult.

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