Serotonin syndrome is an unexpected fatal adverse event related to serotonergic medication. This case report is the first report describing the possible treatment effect of famotidine on serotonin syndrome. Furthermore, this is the first case report of serotonin syndrome induced by meperidine alone in a patient with no previous history suggesting a susceptibility to serotonin syndrome. A 70-year-old male with no recent history of serotonergic drug use presented with severe serotonin syndrome following ureteroscopy, possibly due to postoperative meperidine administration. The patient's symptoms included hypertension, tachycardia, tachypnea, hyperthermia, myoclonus, diaphoresis, retching, nausea, agitation, and semicoma mentality with no pupillary light reflex. Symptoms began to subside immediately after the administration of intravenous famotidine for prevention of aspiration pneumonia, with mental and neurological symptoms showing improvement initially, followed by autonomic symptoms. This case report suggests that the histamine type 2 receptor antagonist famotidine may be an effective emergency treatment for serotonin syndrome.