Prascend is a prescription medication used to treat equine Cushing’s disease, formally known as pituitary pars intermedia dysfunction (PPID). It contains the active ingredient pergolide mesylate and was first approved by the FDA in 2011. It remains the only branded drug specifically licensed for this condition in horses, though a generic version called Zygolide has since been approved.
What PPID Does to Your Horse
PPID affects hormone production pathways in the brain, specifically the hypothalamus and pituitary gland. In a healthy horse, dopamine keeps the pituitary’s middle section (the pars intermedia) in check, preventing it from overproducing certain hormones. In horses with PPID, that control breaks down. The pituitary floods the body with excess hormones, including ACTH and others that trigger a cascade of visible problems.
The most recognizable sign is a long, curly coat that doesn’t shed normally. But PPID goes well beyond appearance. Affected horses commonly develop muscle wasting along the topline, a potbelly, excessive thirst and urination, lethargy, and fat deposits on the crest of the neck, tailhead, and above the eyes. Laminitis is one of the most serious complications and often what prompts owners to seek a diagnosis in the first place.
Horses with PPID also have weakened immune systems. They’re more prone to chronic skin infections, pneumonia, sinus infections, abscesses, slower wound healing, and heavier parasite burdens. These secondary problems can become just as dangerous as the hormonal imbalance itself.
How Prascend Works
Pergolide is a synthetic compound that mimics dopamine in the brain. By stimulating dopamine receptors directly, it restores the braking mechanism that PPID has disrupted. This brings down the elevated levels of ACTH and other hormones driving the disease’s symptoms. The drug doesn’t cure PPID, but it controls the hormonal excess that causes the clinical signs. Most horses stay on it for the rest of their lives.
Because pergolide activates dopamine receptors broadly, it also suppresses the hormone prolactin. This means it can interfere with milk production, which matters if you’re dealing with a lactating mare.
Starting Dose and Adjustments
The standard starting dose is 2 micrograms per kilogram of body weight, given by mouth once daily. For a typical 1,000-pound horse, that works out to about 1 mg per day, which is one tablet. Your vet will reassess in roughly 30 days, looking at both clinical signs and bloodwork to decide whether the dose needs to go up.
The goal is finding the lowest effective dose for your individual horse. If symptoms haven’t improved enough after that first month, the dose can be increased in small increments every 30 to 60 days. The maximum labeled dose is 4 micrograms per kilogram daily, or about 2 mg for an average-sized horse. Some horses respond quickly at the starting dose, while others need gradual increases over several months to get their hormone levels under control.
Side Effects and the “Pergolide Veil”
The two most common side effects are loss of appetite and mild depression or lethargy. Horse owners sometimes call this the “pergolide veil” because it can make an otherwise alert horse seem dull and disinterested in food, particularly in the first days or weeks of treatment or when the dose is bumped up too quickly.
If your horse shows signs of dose intolerance, the standard approach is to cut the dose in half for three to five days, then gradually work back up in small increments every two weeks. Most horses adjust within a short period once the dose is managed carefully. The veil is temporary, not a sign that the horse can’t tolerate the drug long term.
Monitoring With Blood Tests
Vets track treatment success through a combination of visible improvement and blood tests measuring ACTH levels. One important detail: ACTH in horses naturally rises during late summer and fall. From mid-July through mid-November, normal ACTH can run as high as 50 pg/mL in many labs, while from mid-November through mid-July, values above 35 pg/mL are considered elevated.
This seasonal pattern matters for two reasons. First, your horse might appear to worsen in autumn even on medication, because the natural ACTH surge can overwhelm the current dose. Some vets temporarily increase the pergolide dose during fall months to compensate. Second, a more specialized diagnostic test (the TRH stimulation test) doesn’t yet have seasonal reference ranges, so the current recommendation is to avoid running it between mid-July and mid-November when results are harder to interpret.
Plan on blood tests at least every few months in the early stages of treatment, and at minimum once or twice a year once your horse is stable on a dose that’s working.
Storage and Practical Tips
Prascend tablets should be stored below 25°C (77°F) and kept in the original blister packaging inside the outer carton to protect them from light. Many owners give the tablet hidden in a small amount of feed or a treat. If your horse is a picky eater, especially during the early adjustment period when appetite may already be reduced, dissolving the tablet in a small syringe of water and administering it orally can ensure the full dose gets in.
Because PPID is a lifelong condition, Prascend is a lifelong commitment. The good news is that most horses respond well. Coats improve, energy returns, muscle condition rebuilds, and the risk of laminitis drops significantly once hormone levels are brought closer to normal. The earlier treatment starts after diagnosis, the more effectively it can slow the progression of the disease and protect your horse from its most serious complications.