Cannabis has long been used for medical and recreational purposes because of its antiemetic, analgesic, and mood effects. Ironically, chronic use of cannabis can result in paradoxical effects, including a condition known as cannabinoid hyperemesis syndrome. Patients with this syndrome often are seen in the ED with cyclic vomiting, nausea, and epigastric pain. Although the definitive treatment of cannabinoid hyperemesis syndrome is discontinuing the causative agent, medical management that includes rehydration is important to prevent complications. Common antiemetic medications are ineffective, but some studies have shown haloperidol and lorazepam to be effective in treating acute symptoms.