Acetylpromazine maleate (Acepromazine)(More commonly known as ACP, Ace, or by the trade name Atravet or "Acezine 2" etc, number depending on mg/ml dose) is one of the phenothiazine derivative psychotropic drugs, used little in humans, however frequently in animals as a sedative and antiemetic. Its principal value is in quietening and calming frightened and aggressive animals. The standard pharmaceutical preparation, acepromazine maleate, is used extensively in equine, feline, and canine; especially as a pre-anesthetic agent often in conjunction with Atropine, and often an opiate such as morphine or buprenorphine. Its depressive cardiopulmonary effects can be profound and as such is not recommended for use in geriatric or debilitated animals, (often substitued with Midazolam in these cases, or left out of the premed cocktail all together).

In horses Acepromazine is normally given by the intramuscular route, taking 30-45 minutes to take effect. It may also be given intravenously (taking only 15 minutes to take effect) or orally. Sedation usually lasts for 1-4 hours, although some horses may feel the effects for up to 24 hours.

Acepromazine is a prohibited class A drug under FEI rules, and its use is prohibited or restricted by many other equestrian organizations. It can be detected in the blood for 72-120 hours, although repeated doses may make it remain present for several months.

Side effects are not common, but the use of acepromazine in stallions is usually considered contraindicated due to the risk of paraphimosis.

Acepromazine should not be used in horses dewormed with piperazine. It lowers blood pressure, and should therefore be used with caution in horses that are experiencing anemia, dehydration, shock, or are colicing.