Last Updated on March 26, 2022 by Allison Price

Chlorpromazine, a tranquilizer phenothiazine1 Although Chlorpromazine can be used to treat nausea in pets and cats, the veterinarians often use it as a centrally acting antiemetic. It has also been used extensively as a calming agent for horses.

Although chlorpromazine doesn’t contain phenothiazine it is still classified as such because of its similar molecular structure. It can also be used to general sedation or for preanesthetic purposes and may sometimes be used as a sedative for cattle, sheep, goats, and swine.


Chlorpromazine, which was first used in 1950, was the prototype of the phenothiazine drug class. Chlorpromazine was first developed in France to be used as a pre-anesthesia for surgery. Patients who received it reported feeling relaxed and calm after they woke up from anesthesia. This breakthrough changed the face of human psychiatric treatment. The “chemical lobotomy” is known as chlorpromazine. It is widely considered to be one of the most important advances in human psychiatric treatment. 2


The use of psychotropic drugs ( tranquilizers and sedatives) to regulate the behavior of horses has caused some controversy in the performance horse industry. These antipsychotic drugs include acepromazine and chlorpromazine . They are used to treat mental disorders such as schizophrenia or bipolar disorder in people.

These concerns can be attributed to the illegal and/or reckless administration of these drugs in horses. The definition of proper dosage can be highly variable and horse-dependent. This is why these medicines should only ever be administered by or under the guidance of a veterinarian.

Side Effects and Dosage

Oral suspensions and solutions for horses of chlorpromazine are the best form of dosage. They can be given either by mouth (with a needle) or mixed with food. They are usually available in concentrations of 10 mg/ml up to 200 mg/ml.

Chlorpromazine’s main side effect is its rigidity in certain muscles. This rigidity can be accompanied with a characteristic tremor in the affected limbs. Dr. Tobin cites a N.N. study in Drugs & the Performance Horse. Booth’s “Psychotrophic drugs and veterinary medicine” described the effects of chlorpromazine on horses.

Booth states that “after a few moments of initial sedation after administration of the drug,” the animal can become unsteady and sink backwards on its hocks. The animal might also be unable to coordinate their movements. Although the horse might stumble and fall, it will then stand upright if they continue to lunge and rearrange. This response is said to alternate with periods of sedation.” 3

Tobin stated, however, that “[T]he benefit with a short-acting medicine [such as chlorpromazine]is that if the response isn’t satisfactory, you can just wait.” Either you try a different dose or you don’t.

1Black W. D. (2003). Veterinary Drug Handbook. The Canadian Veterinary Journal 44(4) HTML297.

3Barrel Horse News

NexGen Pharmaceuticals

NexGen Pharmaceuticals, a leading veterinary compounding pharmacy in the country, offers both sterile and unsterile compounding services. NexGen is different from other veterinary compounding pharmacies. We focus on difficult-to-find drugs or those that have not been made commercially, but still meet a critical need. We are also experts in wildlife pharmaceuticals including sedatives as well as their antagonists. This allows us to offer many unique options for zoo animals and wildlife immobilization, anesthesia, and other requirements.

To provide better care for our veterinary patients, pharmacists should also be encouraged to build strong working relationships with veterinarians. These relationships help to build a greater knowledge base for pharmacists and vets, which makes them both more efficient in their professional roles.

Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!