Olney's lesions, also known as NMDA receptor antagonist neurotoxicity (NAN), are a form of potential brain damage due to drugs that have been studied experimentally and have produced neuronal damage, yet are administered by doctors to humans in the settings of pharmacotherapy and of anesthesia. They are named after John Olney, who conducted a study in 1989 to investigate neurotoxicity caused by PCP and related drugs.

They are important for two reasons. Firstly, NMDA receptor antagonists are physician-prescribed drugs for therapeutic treatment of human diseases such as memantine for Alzheimer's disease and amantadine for Parkinson's disease, and also occur as street drugs that are taken recreationally. Secondly, in the field of anesthesiology, the dissociative anesthesia of many general anesthetics is due to NMDA receptor antagonist properties. Because the neuronal vacuolation of Olney's lesions evolves into neuronal necrosis or death of neurons, it is important to determine whether Olney's lesions occur in humans, not only in experimental animals. The essential question is whether an NMDA receptor antagonist drug is to be considered a human neurotoxin or not. The patient safety implications for pharmacotherapy and for anesthesia would each be profound, if the answer is affirmative.