Omeprazole 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.

Omeprazole is a proton pump inhibitor (PPI) that lowers stomach acid production. In horses, it is best known as the active ingredient in GastroGard, the FDA-approved oral paste labeled for treatment and prevention of recurrence of gastric ulcers in horses and foals 4 weeks of age and older.

This medication works by blocking the acid pump in stomach parietal cells. Less acid means the stomach lining has a better chance to heal, especially when ulcers are linked to training, intermittent feeding, stall confinement, travel, illness, or other stressors.

For many horses, omeprazole is only one part of the plan. Your vet may also recommend changes in forage access, meal timing, training intensity, turnout, and NSAID use. That matters because medication can reduce acid, but management changes often help reduce ulcer recurrence.

Because absorption and response can vary between horses, your vet may tailor the product, timing, and treatment length to your horse's history and whether the concern is equine squamous gastric disease or equine glandular gastric disease.

Omeprazole is used most often for equine gastric ulcer syndrome (EGUS). That includes ulcers affecting the squamous portion of the stomach and, in some cases, glandular disease. It is the only FDA-approved medication for treatment of gastric ulcers in horses, and it is also labeled to help prevent ulcers from coming back after an initial treatment course.

Your vet may consider omeprazole when a horse has signs that fit ulcers, such as poor appetite, weight loss, attitude changes, recurrent mild colic, poor performance, girthiness, or discomfort after eating. In many horses, diagnosis is confirmed with gastroscopy because ulcer signs can overlap with other digestive problems.

It may also be used in horses considered high risk for ulcers, including racehorses, performance horses, horses in heavy work, foals, and horses receiving medications or management that may irritate the stomach. In glandular disease, your vet may pair omeprazole with other medications such as sucralfate or misoprostol rather than using a one-drug approach.

Omeprazole does not treat every cause of colic, poor appetite, or weight loss. If your horse has severe pain, fever, diarrhea, choke, or sudden decline, see your vet promptly rather than assuming ulcers are the cause.

Always follow your vet's instructions, because the right dose depends on your horse's weight, diagnosis, and treatment goal. For FDA-approved GastroGard paste, the labeled treatment dose for gastric ulcers is 4 mg/kg by mouth once daily for 28 days. To help prevent recurrence after treatment, the labeled maintenance dose is 2 mg/kg by mouth once daily for at least another 28 days.

In practical terms, one GastroGard syringe contains enough omeprazole to treat a 1,250 lb (568 kg) horse at the full 4 mg/kg dose for one day. The syringe is weight-marked, so your vet can show you how to set the plunger correctly. For recurrence prevention, the same syringe can dose twice that body weight because the dose is half as much.

Timing matters. The product insert reports that absorption is reduced when horses are fed, so many vets prefer dosing before feeding when possible. If your horse is also taking sucralfate, spacing the medications apart is important because sucralfate may reduce omeprazole absorption. Your vet may also recommend a longer course, repeat scoping, or combination therapy for glandular disease.

Do not change the dose, stop early, or switch to a compounded or human product without your vet's guidance. Horses vary, and underdosing can make treatment less effective while delaying a clear answer about whether ulcers are truly present.

Most horses tolerate omeprazole well, and labeled safety studies found no treatment-related adverse effects even at doses much higher than the standard daily dose. That said, any medication can cause problems in an individual horse, so it is still worth monitoring closely.

Possible side effects reported with omeprazole products include decreased appetite, mild colic signs, gas, diarrhea, or other digestive upset. If your horse seems more uncomfortable after starting the medication, stops eating, develops diarrhea, or shows worsening abdominal pain, contact your vet. Those signs may reflect the medication, the underlying ulcer disease, or a different problem entirely.

Longer-term acid suppression in horses is an area your vet may discuss in more detail for horses needing extended therapy. In some cases, your vet may want to reassess with gastroscopy rather than continuing treatment indefinitely.

See your vet immediately if your horse has severe colic, repeated rolling, marked depression, dehydration, trouble swallowing, or a sudden drop in manure output. Those are not signs to monitor at home while waiting for the next dose.

The most important practical interaction in horses is with sucralfate. Sucralfate can interfere with absorption of oral omeprazole if given too close together, so your vet may recommend giving omeprazole first and waiting 60 to 90 minutes before sucralfate.

Your vet will also look at the full medication list, especially if your horse is receiving NSAIDs such as phenylbutazone or flunixin meglumine, because those drugs can contribute to stomach irritation or ulcer risk. Omeprazole is often used alongside them in selected cases, but that does not make NSAID-related risk disappear.

Other interactions are less clearly defined in horses than in people, but acid suppression can change how some oral medications are absorbed. That is one reason your vet should know about every paste, powder, supplement, and compounded product your horse receives.

Do not add over-the-counter human acid reducers, ulcer supplements, or compounded omeprazole on your own. Combining products can make dosing confusing and may reduce effectiveness or complicate follow-up.