Gacyclidine (GK11) is a derivative of phencyclidine with neuroprotective properties. Tritiated gacyclidine and its enantiomers bind to NMDA receptors with binding parameters similar to those of other non‐competitive NMDA receptor antagonists. Beneficial effects of gacyclidine include reduction of lesion size and improvement of functional parameters after injury. In traumatic brain injury models, gacyclidine also improves behavioral parameters and neuronal survival. In an animal model of Amyotrophic lateral sclerosis (ALS), functional alteration of locomotor activity was evident and improved the survival of mice, suggesting that chronic administration of gacyclidine beginning at early symptomatic stage may be beneficial for patients with ALS. Gacyclidine has also been associated with altered mental status and end organ damage in patients.