Verbal IQ affected by smoking marijuana as in early teens: study

Washington: Teenagers beware! Smoking marijuana as early as 14 may worse your verbal IQ and cognitive abilities by the time you turn 20, warns a study.

Researchers from Universite de Montreal in Canada suggest that there may be little ill-effect if teenagers delay smoking marijuana till the age of 17.

The findings, published in the journal of Development and Psychopathology, indicate that the adolescents, who smoke pot as early as 14, do worse by 20 on some cognitive tests and tend to drop out of school sooner, which helped to explain the decrease in their verbal abilities.

"Overall, these results suggest that, in addition to academic failure, fundamental life skills necessary for problem-solving and daily adaptation [...] may be affected by early cannabis exposure," said the study.

However, the cognitive declines associated with cannabis do not seem to be global or widespread, cautioned the study's lead author, Natalie Castellanos-Ryan.

The team looked at 294 teenagers and completed a variety of cognitive tests at ages 13, 14 and 20 and filled out a questionnaire once a year from ages 13 to 17 and again at 20, between 1991 and 1998.

The study found links between cannabis use and brain impairment only in the areas of verbal IQ and specific cognitive abilities related to frontal parts of the brain, particularly those that require learning by trial-and-error.

In addition, if teenagers hold off until 17 years before smoking their first joint, those impairments are no longer discernible.

"We found that adolescents who started using cannabis at 17 or older performed equally well as adolescents who did not use cannabis," Castellanos-Ryan added.

The findings indicate that 43 percent of the participants reported smoking pot at some point during that time, most of them only a few times a year.

At 20 years of age, 51 percent said they still used the drug. In general, those who started early already had short-term memory and poor working memory.