In a new report, the American Academy of Pediatrics says pot should be avoided during pregnancy and breastfeeding. Marijuana’s main mind-altering ingredient was detected in nursing mothers’ breast milk in a study that comes amid evidence that more U.S. women are using pot during pregnancy and afterward. Experts say the ingredient, THC, has chemical properties that could allow it to disrupt brain development and potentially cause harm, although solid evidence of that is lacking. The new study involved 50 nursing mothers who were using pot and provided breast milk samples to researchers at the University of California, San Diego. Lab testing found small amounts of THC, the psychoactive chemical that causes marijuana’s “high,” in 34 of 54 samples up to six days after they were provided. Another form of THC and cannabidiol, a pot chemical touted by some as a health aid, were detected in five samples. The study authors said, “it is reasonable to speculate” that exposing infants to THC or cannabidiol “could influence normal brain development,” depending on dose and timing.

This article originally appeared on Chicago Tribune. Click here to read the full article on Chicago Tribune.