Cannabinoid hyperemesis syndrome (CHS) is typically unresponsive to conventional pharmacologic antiemetics, and patients often require excessive laboratory and radiographic testing and hospital admission. We report 4 cases of CHS that failed standard emergency department therapy but improved significantly after treatment with haloperidol. Although the exact mechanism for CHS remains unclear, dysregulation at cannabinoid type 1 seems to play a role. Recent animal data demonstrate complex interactions between dopamine and cannabinoid type 1 signaling, a potential mechanism for haloperidol success in patients with CHS. Our success with haloperidol in these 4 patients warrants further investigation of haloperidol as an emergency department treatment for CHS.