(HealthDay News) — The potential effect of cannabis on brain structure remains a subject of intense scientific scrutiny, but mixed results have emerged from two of the latest studies on the topic. Both studies were published online August 26 in JAMA Psychiatry.
In one study, Arpana Agrawal, PhD, an associate professor of psychiatry at the Washington University School of Medicine in St. Louis, and colleagues performed brain scans on 483 twins or siblings as young adults, 262 of whom reported they’d used cannabis at least once. Cannabis users were found to have smaller amygdalas than nonusers, a result that agreed with earlier findings, Agrawal told HealthDay.
But the researchers found that brain volumes did not differ significantly between twins or siblings, even if one had used cannabis and the other had not, Agrawal said. Both siblings showed smaller amygdalas, regardless of cannabis use. Based on this, common genetic factors might influence amygdala size as well as one’s propensity to experiment with cannabis. Some environmental factor could also be at play. For example, childhood exposure to adversity can affect amygdala size, and also can make a person more likely to try drugs.
In the other study, Tomas Paus, MD, PhD, a senior scientist at the Rotman Research Institute in Toronto, and colleagues analyzed brain scans and data from three other large-scale studies, amassing a pool of 1,574 participants, ages 12–21. The researchers found that men who reported using cannabis in early adolescence had lower cortical thickness than those who did not, but only if they had a high genetic predisposition toward schizophrenia. The results indicate that cannabis might have some effect on the developing brains of at-risk male teenagers, the researchers conclude. However, no similar effect was found in low-risk men or in women.