U.K. regulators issued guidance on Thursday, warning weight loss and diabetes medications may weaken the effectiveness of birth control and may be harmful in pregnancy.

Anecdotes abound about “Ozempic babies”—when women wound up with unplanned pregnancies while taking both birth-control and the popular GLP-1 drugs for diabetes or weight loss.  But today marks the first official agency warning about the possibility of these drugs—specifically Mounjaro—decreasing the effectiveness of oral contraceptives.