Acepromazine is a phenothiazine derivative antipsychotic drug. Acepromazine is frequently used in animals as a sedative and antiemetic. Its principal value is in quietening and calming anxious animals. The standard pharmaceutical preparation, acepromazine maleate, is used in veterinary medicine in dogs, and cats. It is used widely in horses as a pre-anaesthetic sedative and has been shown to reduce anaesthesia related death. However, is contraindicated in stallions due to the risk of paraphimosis and persistent priapism. Its potential for cardiac effects, namely hypotension due to peripheral vasodilation, can be profound and as such is not recommended for use in geriatric or debilitated animals, especially dogs. In these cases it is most often substituted with midazolam or diazepam and left out of the preanesthetic medication altogether.