Two studies published by The BMJ today find no links between prescription opioids or macrolide antibiotics taken during pregnancy and risk of major birth defects. Both opioids (painkillers) and macrolides (antibiotics) are often prescribed during pregnancy. Some previous studies have reported associations between exposure to opioids and macrolides and certain birth defects, but results are inconsistent. Two studies published today set out to address this uncertainty. The first study involved data for more than 82,000 US women who received two or more prescriptions for any opioid during early (first trimester) pregnancy from 2000 to 2015.