Years ago, pergolide was used to treat Parkinson's disease in people. Due to increased risk of heart disease, the Food and Drug Administration withdrew it from the human market in 2007. It is still the staple medication for equine Cushing's syndrome, technically called pituitary pars intermedia dysfunction, or PPID. Cushing' s syndrome is common in older equids, with symptoms including long hair that doesn't shed out, laminitis, frequent urination and water consumption and abnormal fat deposits. Pergolide is available from compounding pharmacies for equine use. It is generally considered safe, with only a few side effects.
Some horses may lose their appetites initially when beginning to take pergolide. Consult the veterinarian about adjusting the dosage to see if appetite picks up. If that doesn't work, try giving the drug in safe, sugar-free treats or mixing it with yoghurt and syringing it into the mouth. Since pergolide is available in powder, tablet and liquid formulations, see if a change in the form of medication will encourage eating. Gradually increasing the dosage of pergolide rather than administering the full dose at once may help avoid this side effect.
According to Dr. Barbara Forney, a Fédération Equestre Internationale (FEI) veterinarian, no testing on pregnant or lactating mares has been done on pergolide, nor have any tests been done on sperm counts in breeding stallions on the drug. In studies on laboratory animals, high doses of pergolide have not caused fetal harm, pergolide's effects on the foetus or foal have been conducted, and no studies regarding abortion in broodmares, it is prudent not to administer to pregnant mares or those intended for breeding.
Dr. Eleanor Kellon, a veterinarian and the editor of the Equine Cushing's Disease and Insulin Resistance website, states that depression in horses given the drug is referred to as the "pergolide veil." Besides lack of appetite, depressed horses appear to lose interest in their surroundings and companions, become lethargic, and those with joint disease or arthritis may be more "ouchy." According to Kellon, this veil usually lifts within two weeks of receiving pergolide, but if it continues, contact your veterinarian.