A new study shows that psilocybin, a psychedelic compound being tested for postpartum depression, may actually cause harm during the breastfeeding period. While the drug helped non-pregnant mice feel less anxious, it made postpartum mothers more anxious and worsened their caregiving behaviors. Even more concerning, baby mice exposed to psilocybin through breast milk developed mood and social problems as adults, suggesting potential lasting risks for human infants.