Omeprazole for Horses: Gastric Ulcers, GastroGard, UlcerGard, and Why Formulation Matters

By Dr Duncan Houston

Quick Answer

Omeprazole is the main acid-suppressing medication used for equine gastric ulcer syndrome, especially equine squamous gastric disease. In the United States, the FDA-approved equine omeprazole oral pastes are GastroGard for treatment and UlcerGard for prevention. Formulation matters because omeprazole is acid-labile, and horses do not reliably absorb standard human or poorly formulated compounded products the same way. (U.S. Food and Drug Administration)

Why Gastric Ulcers Are So Common in Horses

Equine gastric ulcer syndrome is one of the most common stomach problems in horses. Risk is especially high in racehorses and other performance horses, and the AAEP notes ulcers affect up to 90 percent of racehorses and 60 percent of show horses. Common risk factors include stall confinement, travel, strenuous exercise, high-grain feeding, and long periods without forage. (AAEP)

That matters because horses are designed to graze almost continuously. Their stomach keeps producing acid, so when management reduces forage and increases stress, the stomach lining pays the price.

What Omeprazole Actually Does

Omeprazole is a proton pump inhibitor. It suppresses gastric acid production by inhibiting the H+/K+ ATPase system in parietal cells. In plain English, it turns down acid at the source, which gives ulcerated tissue a chance to heal.

For equine squamous gastric disease, acid suppression is the cornerstone of treatment. Glandular disease is more complicated and may not respond as predictably, which is why not every “ulcer horse” is the same case with the same plan. (Merck Veterinary Manual)

GastroGard vs UlcerGard

In the U.S., the FDA-recognized equine omeprazole products are:

• GastroGard: approved equine omeprazole oral paste used for treatment of gastric ulcers in horses and foals 4 weeks of age and older. (animaldrugsatfda.fda.gov)

• UlcerGard: FDA-approved equine omeprazole oral paste used to prevent gastric ulcers in horses. (Federal Register)

Practically, people often think of them as:

• GastroGard for treatment

• UlcerGard for prevention or high-risk periods

That is the cleanest way to think about it.

Why Formulation Matters So Much in Horses

This is the part many owners miss.

Omeprazole is acid-labile, which means it can be degraded by acid before it gets where it needs to go. Horses also do not absorb human omeprazole formulations particularly well. The Merck Veterinary Manual states that a specific equine product was developed because oral bioavailability of human or compounded formulations is poor in horses. Research also notes that bioavailability improves with buffered or enteric-coated equine formulations. (Merck Veterinary Manual)

So this is not just branding. It is a drug-delivery issue.

A product can contain omeprazole on paper and still perform poorly in a horse if the formulation is wrong.

What the FDA Position Means in Real Life

FDA sources currently identify GastroGard and UlcerGard as the FDA-approved omeprazole products for horses. Recent FDA warning letters have also addressed compounded omeprazole products that were copies of approved equine products, reinforcing that there are already approved omeprazole pastes for horses on the market. (U.S. Food and Drug Administration)

Clinically, that means two things:

1. Approved equine products are the standard reference point in the U.S.

2. Owners should be cautious about assuming every paste, powder, or compounded product is equivalent

Not all omeprazole products for horses are interchangeable just because the label says omeprazole.

What Vets Actually Worry About

When a horse has ongoing ulcer signs despite “being on omeprazole,” the big questions are:

• Is the horse actually getting an effective equine formulation?

• Is the drug being given properly?

• Is this really squamous disease, glandular disease, or both?

• Are management factors still driving the problem?

• Is there another diagnosis being missed?

That is why a horse can “fail omeprazole” on paper when the real problem is formulation, timing, or the wrong ulcer category.

When Omeprazole Is Used

Omeprazole is commonly used for:

• confirmed or strongly suspected equine squamous gastric ulcer disease

• prevention during high-risk periods such as travel, competition, stall confinement, and intense training

• recurrence prevention in horses with a known history of ulcers (animalhealth.boehringer-ingelheim.com)

For glandular disease, treatment is often less straightforward and may require longer courses, additional medications, and management changes. Merck notes that while omeprazole is approved for a 28-day treatment course for EGUS, glandular disease may require 45 to 60 days of treatment, often guided by repeat gastroscopy. (Merck Veterinary Manual)

Dosing Basics

The labeled equine dosing is different depending on whether you are treating ulcers or preventing them.

• GastroGard treatment dosing is 4 mg/kg once daily for 4 weeks. (docs.boehringer-ingelheim.com)

• UlcerGard prevention dosing is 1 mg/kg once daily. (docs.boehringer-ingelheim.com)

This is one reason owners should not bounce between products casually and assume they are using the same regimen. Same drug, different purpose, different dose.

Administration Tips That Actually Matter

How you give omeprazole affects how well it works.

Recent review literature notes that oral omeprazole has better bioavailability in fasted horses and is generally preferred after a period of fasting and before a meal. (PMC)

That means:

• timing matters

• feeding pattern matters

• management still matters

The drug is important, but it is not a magic wand over a high-stress, low-forage management system.

Common Signs of Ulcers in Horses

Signs can be vague, which is part of why ulcer cases get missed or misread.

Possible signs include:

• poor performance

• behavioral change

• irritability when girthing

• reduced appetite

• weight loss or failure to thrive

• mild recurrent colic

• poor body condition

Some horses read like drama queens. Some read like almost nothing at all.

Common Mistakes Owners Make

Assuming all ulcer cases are the same

They are not. Squamous and glandular disease do not behave exactly the same way. (Merck Veterinary Manual)

Buying based on price alone

A cheaper product that does not deliver useful drug exposure is not actually cheaper.

Ignoring management

If forage is inadequate and stress stays high, recurrence risk stays high. (AAEP)

Treating without confirming the problem

Ulcers are common, but they are not the only cause of poor performance, girthiness, or colic.

When to Call Your Vet

Get veterinary advice if your horse has:

• repeated mild colic

• poor appetite

• weight loss

• resistance under saddle

• chronic performance decline

• recurrent ulcer history

• ulcer signs that persist despite treatment

If a horse is not responding as expected, that is when you need to reassess diagnosis, formulation, dosing, timing, and management.

Frequently Asked Questions

Is omeprazole the best ulcer medication for horses?

For equine squamous gastric ulcer disease, omeprazole is the mainstay of treatment. Glandular disease is more complicated and may need a broader plan. (Merck Veterinary Manual)

What is the difference between GastroGard and UlcerGard?

GastroGard is used for treatment at a higher labeled dose, while UlcerGard is used for prevention at a lower labeled dose. (docs.boehringer-ingelheim.com)

Are human omeprazole products the same as equine omeprazole paste?

No. Horses absorb these differently, and Merck specifically notes that human or compounded formulations have poor oral bioavailability in horses compared with the equine product. (Merck Veterinary Manual)

Do compounded omeprazole products always work the same?

No. They should not be assumed equivalent to approved equine products. FDA and pharmacology sources both support caution here. (U.S. Food and Drug Administration)

How long do horses stay on omeprazole?

That depends on whether the goal is treatment or prevention, and whether the horse has squamous disease, glandular disease, or recurrent risk. Standard treatment for labeled equine ulcer therapy is 28 days, but some cases need longer reassessment. (docs.boehringer-ingelheim.com)

Should omeprazole be given before or after feeding?

Evidence supports giving oral omeprazole after a fasting period and before a meal for better bioavailability. (PMC)

Can ulcers come back after treatment?

Yes. Recurrence is common if risk factors remain or if prevention is not addressed. (Merck Veterinary Manual)

Do all performance horses have ulcers?

No, but prevalence is high in some groups, especially racehorses and show horses. (AAEP)

Final Thoughts

Omeprazole remains one of the most important medications in equine ulcer management, but horses are a perfect example of why drug formulation matters just as much as the active ingredient itself.

If you are treating equine gastric ulcers, the real question is not just “Is this omeprazole?”
It is “Is this the right equine formulation, used the right way, for the right ulcer problem?”

That is a much better question, and it leads to much better outcomes.

If you are trying to work out whether your horse’s signs fit ulcers, whether treatment is working, or whether prevention makes sense during travel and competition, ASK A VET™ can help you make sense of the next step.