Side effects include salivation, sweating, diarrhea, elevated blood glucose, decreased intestinal motility, and the risk of early labour with retained placenta, if given to a pregnant mare in the last trimester of pregnancy.These drugs should not be used with horses who have certain health problems including heart disease, respiratory dysfunction, seizures, or those who are in shock.They do also reduce normal inhibitions, so a horse that usually wouldn’t kick you may kick you when sedated.” Acepromazine takes about 30 minutes to take effect and will last eight hours or longer.It does not relieve pain, so should not be used to control the horse for painful procedures.One is fluphenazine, a long-acting sedative that can last for four weeks or longer.
The alpha-2 adregenic agonists (A2As) work more quickly, taking effect within five minutes, so tend to be preferred by vets. A2As are often recommended for procedures that might cause the horse pain, because they have an analgesic effect, and are often used in horses with colic.
For a consistently hot or anxious horse, feeding extra magnesium in a supplement may be helpful.
Overdosing can cause heart problems and diarrhea, however.
Reserpine is another human medication with similar effects.
One serious risk to these sedatives, especially fluphenazine is that the horse may ‘freak out,’ according to Dowling, and react by climbing over a stall wall or attempting to escape in other ways that can cause serious injury.
Dowling pointed out ‘it’s important not to ‘trust’ the sedation.