Pergolide for Horses: Uses, Dosing & Side Effects

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Pergolide is a prescription medication used in horses to help control pituitary pars intermedia dysfunction (PPID), often called equine Cushing's disease. It is a dopamine receptor agonist and an ergot derivative, which means it acts on the pituitary gland to reduce abnormal hormone signaling. In the U.S., labeled pergolide tablets for horses include Prascend and, as of January 9, 2026, the FDA-approved generic Zygolide. Your vet may recommend one of these products for long-term PPID management.

PPID is common in older horses and can cause a long or curly hair coat, delayed shedding, muscle loss, increased drinking and urination, lethargy, recurrent infections, and sometimes laminitis. Pergolide does not cure PPID, but it can help control the clinical signs and improve day-to-day comfort when paired with good husbandry, hoof care, dental care, and nutrition planning.

Most horses need pergolide once daily by mouth for months to years. Improvement is usually gradual, not immediate. Merck notes that clinical improvement is often seen within 6 to 12 weeks, so follow-up with your vet matters when deciding whether the dose is working well for your horse.

Pergolide is used primarily for the control of clinical signs associated with PPID in horses. That is the FDA-labeled indication for equine pergolide tablets. In practice, your vet may prescribe it when a horse has compatible signs and supportive testing, such as elevated endogenous ACTH or an abnormal TRH stimulation test.

The goal is not to treat one symptom in isolation. Instead, pergolide helps reduce the hormone imbalance driving the disease. Horses may improve in coat shedding, attitude, body condition, drinking and urination patterns, and overall comfort. Some horses also have fewer secondary problems related to PPID, such as poor immune resilience.

Pergolide is especially important to discuss if your horse has PPID plus insulin dysregulation or a history of laminitis. Those horses often need a broader management plan that includes diet changes, hoof support, and repeat monitoring. Medication is one part of care, not the whole plan.

Pergolide dosing for horses should always come from your vet. The labeled starting dose is 2 mcg/kg by mouth once daily, with dose adjustments based on clinical response and follow-up endocrine testing. The product label says the dose should not exceed 4 mcg/kg daily. Merck also notes that many horses are ultimately maintained around 0.5 to 1 mg per horse once daily, though individual needs vary.

Because tablets are 1 mg and scored, your vet may round the dose to the nearest half-tablet. On the label's dosing table, horses weighing 300 to 749 lb start at 0.5 tablet daily, 750 to 1,249 lb start at 1 tablet daily, 1,250 to 1,749 lb start at 1.5 tablets daily, and 1,750 to 2,249 lb start at 2 tablets daily. Your vet may adjust from there after recheck exams and lab work.

If a horse shows signs of dose intolerance, the label recommends reducing the dose by half for 3 to 5 days, then slowly titrating back up in 2 mcg/kg increments every 2 weeks until the desired effect is reached. Some horses tolerate pergolide better when the dose is split every 12 hours, but that decision should come from your vet.

Do not crush pergolide tablets unless your vet specifically instructs you on safe handling. The product labeling warns that split or crushed tablets may cause eye irritation, irritating odor, or headache in people, and crushing can increase human exposure.

The most common side effect pet parents notice is decreased appetite. In the pre-approval field study for Prascend, decreased appetite was reported in 32.8% of treated horses. Other reported effects included lethargy, diarrhea or loose stool, colic signs, and abnormal weight loss. Merck also lists listlessness and anorexia as recognized adverse effects.

Many side effects are mild and happen early, especially in the first month of treatment or after a dose increase. Some horses also show behavior changes, such as agitation, increased activity, or aggression. Post-approval reports have included hyperhidrosis, alopecia, dermatitis, muscle stiffness, ataxia, tremors, seizures, anemia, and elevated liver enzymes, although these are less common.

Call your vet promptly if your horse stops eating, seems unusually dull, loses weight, develops diarrhea, shows colic signs, or acts neurologically abnormal. Do not stop or change the medication on your own unless your vet tells you to. In some horses, a temporary dose reduction and slower titration can improve tolerance.

Keep pergolide away from dogs, cats, and other animals. The label specifically warns that accidental ingestion by other species can cause adverse reactions, and dropped tablets should be picked up right away.

Pergolide can interact with medications that affect dopamine signaling. The product label says dopamine antagonists should generally not be given at the same time because they may reduce pergolide's effect. Examples listed include phenothiazine neuroleptics, domperidone, and metoclopramide. If your horse needs one of these drugs, your vet can help weigh the tradeoffs.

The label also advises caution with drugs that affect protein binding, because pergolide is reported to be about 90% plasma protein bound. That does not mean a combination is automatically unsafe, but it does mean your vet may want closer monitoring when multiple medications are used together.

There is also a practical safety issue for people in the barn. Pergolide is an ergot derivative, so people with prior reactions to ergot drugs should avoid handling it. Pregnant or lactating women should wear gloves when administering tablets, and tablets should not be crushed because that can increase human exposure.

Always give your vet a full medication and supplement list, including ulcer medications, pain relievers, reproductive drugs, and any compounded products. That helps your vet choose the safest dosing plan and decide when recheck testing is needed.