In 2006, psychiatrist Carlos A. Zarate Jr, MD, and colleagues at the National Institute of Mental Health (NIMH) published a seminal finding in Archives of General Psychiatry (now JAMA Psychiatry): A single intravenous dose of ketamine—an anesthetic agent with hallucinogenic properties—produced robust antidepressant effects in patients with treatment-resistant depression (TRD) compared with placebo. The effects of the glutamatergic modulator were observed within 2 hours, far sooner than selective serotonin reuptake inhibitors (SSRIs), and persisted for a week.