Cannabis use in pregnancy affects the fetus’ immune system… leading to anxiety and hyperactivity.

Scientific American reports on a PNAS study that linked increased anxiety, hyperactivity and aggression in children to cannabis use by their parents during pregnancy. It’s easy to imagine why stoner parents might lead to anxious babies after they’re born, but the weird thing here is that the behavioral changes seem to be linked to immune-system genes in the placenta being triggered by cannabis use:

Today pregnant people “are being bombarded with a lot of ads to treat nausea and anxiety during pregnancy” with cannabis, says the paper’s senior author Yasmin Hurd, director of the Addiction Institute at Mount Sinai. “Our studies are about empowering them with knowledge and education so that they can make decisions.”

Hurd and her colleagues worked with 322 parent-child pairs, beginning with profiles of genetic activity in placental samples taken at birth. When the children reached about three years of age, samples of their hair were tested for levels of stress hormones. From ages three to six, they also underwent recordings of their heart-rate variability, another indicator of stress response, and evaluations for anxiety, aggression and hyperactivity. The researchers used statistical methods to exclude effects from cigarette smoking, parental anxiety and other factors that could confuse associations with cannabis use.

In the placental tissues, gene activity was altered with cannabis exposure during pregnancy: genes related to the inflammatory response showed decreased function. Anxiety and hyperactivity levels were higher in children from cannabis-exposed pregnancies and were associated with the placental gene patterns. The researchers speculate that a decline in the activity of immune-related genes in the placenta might explain the behavioral findings.

You can read Hurd’s research here, in the Proceedings of the National Academy of Sciences of the U.S.A.