Diphenidol, a nonphenothiazinic antiemetic agent used primarily in patients with Meniere disease and labyrinthopathies to treat vomiting and vertigo, is considered to be a relatively safe drug. Since it was first approved in the United States in 1967, this drug has been widely used in Latin America and Asia and has contributed to sporadic suicidal and accidental poisonings in mainland China and Taiwan. The mechanism by which diphenidol exerts its antiemetic and antivertigo effects is not precisely known. It is thought to diminish vestibular stimulation and depress labyrinthine function and as an antimuscarinic agent. An action on the medullary chemoreceptive trigger zone may also be involved in the antiemetic effect. Diphenidol has no significant sedative, tranquilizing, or antihistaminic action. It has a weak peripheral anticholinergic effect. Diphenidol is used to relieve or prevent nausea, vomiting, and dizziness caused by certain medical problems.