Males who smoke marijuana in early adolescence have a high genetic risk for schizophrenia, according to an observational study involving 1,577 participants.

Investigators analyzed:

• data about participants’ use of cannabis.

• imaging studies of their brains.

• their polygenic risk score for schizophrenia across 108 genetic loci.

Researchers measured cortical thickness taken from MRI images, and applied linear regression tests to look at the link between cannabis use, cortical thickness, and risk score.

Researchers saw a negative association between cannabis use in early adolescence and cortical thickness in males with a high polygenic risk score. The did not observe such a link in males with low-risk scores, or for any females.

The authors were careful to note that their study did not prove causality, as it is possible that some with a certain developmental trajectory could be more likely to experiment with marijuana (vs use impacting the trajectory).

Citation: French L, Gray C, Leonard G, et al. Early cannabis use, polygenic risk score for schizophrenia and brain maturation in adolescence. JAMA Psychiatry. 2015; August 26, 2015. doi:10.1001/jamapsychiatry.2015.1131.