A new warning from the Centers for Disease Control and Prevention highlights another dangerous development in the opioid crisis: the increasing presence of medetomidine in the illegal fentanyl supply across the United States. Medetomidine is a veterinary sedative that is not approved for human use. It is commonly used in dogs for sedation and pain management, but it is now being detected in street drugs—particularly fentanyl mixtures—throughout the Northeast and