New research from Washington University School of Medicine (led by pharmacologist Tao Che) found that ketamine directly binds to and activates opioid receptors, not just the NMDA receptors it’s known for. Using cryo-electron microscopy, the team saw ketamine sitting in the same binding pocket that conventional opioids use. In mouse studies, blocking opioid receptors wiped out ketamine’s pain relieving effect, showing that opioid activity plays a real role. Researchers caution ketamine’s effects still involve multiple systems, and it’s unclear if this explains its antidepressant benefits.