This review of serotonin syndrome or serotonin toxicity covers the years 2014 to 2019, including information on pathophysiology, etiology, and diagnosis, 3 criteria for diagnosing serotonin syndrome, and criteria for neuroleptic malignant syndrome.The review highlights the potential lethal combinations of commonly prescribed medications used to treat both veteran and nonveteran patients and includes the latest information on offending medications.Prevention of serotonin toxicity includes informed clinicians, patient education, careful prescribing and monitoring, and avoidance of multidrug regimens.