A new study suggests that cannabis smoking affects teenagers more than drinking alcohol. It seems that marijuana impacts thinking, memory, and behavior even after people stop using it.

The research, published in the American Journal of Psychiatry, followed 3,826 students starting from age 13 in the Greater Montreal area. The team studied the kids for four years. Each year they asked them questions about their cannabis and alcohol usage, and used computer-based cognitive tests conducted at school to estimate their brain skills. They then compared how the two substances affected these test results.

Three-quarters of the teenagers interviewed admitted to drinking alcohol at least occasionally. Only 28 percent of the study subjects smoked pot. But while the fraction of users was lower, the effects from the drug were more prominent and longer lasting, and increased with increased cannabis usage.

Smoking pot was found to affect working memory, the control of inhibition, and reasoning. Its effects were independent of alcohol-related effects. This doesn’t minimize the effect of alcohol on teenage brains. Both substances lead to common problems related to learning, attention, and decision making.  

"Their brains are still developing but cannabis is interfering with that," lead author Professor Patricia J Conrod told BBC News. "They should delay their use of cannabis as long as they can."

The effects that cannabis use has on a person's brain are not the same for everyone and depend on several factors. Age of the smoker, frequency of use, dose, and duration all play a part. Previous findings suggest that cannabis can cause changes to brain activity and structure, particularly if used during developmental years. For example, it can impact the development of the brain's white matter, which is important in transmitting nerve signals. 

Studies have also looked at the connection between cannabis use and mental illness. Some correlations have been found in various studies but the link is not straightforward as many factors are involved. Even the idea that cannabis use increases the risk of psychosis should be discussed with caution. While it can contribute, family history, genetic predisposition, and childhood abuse are also crucial risk factors to consider.    

[H/T: BBC News]