Why it’s important: Now that more states are legalizing it, moms may think of marijuana as a relatively harmless way for them to de-stress. Plus, some pregnant women use it to quell morning sickness. But THC likes to bind to fat molecules, which are abundant in breast milk. “Almost nothing is known about the effects of marijuana exposure on a baby’s growing brain,” says Dr. Kemper. “This particular study was one of the first to start to find evidence-based answers.” Even though THC levels were found to be low in the breast-milk samples, marijuana still lingers in the body, so pumping and dumping after using weed is not a reliable strategy. For now, the AAP advises that you play it safe and not use marijuana while pregnant or breastfeeding.