Key Takeaways

• Equine Gastric Ulcer Syndrome affects an estimated 50 to 90% of horses, with performance horses at the highest end of that range¹
• Omeprazole is the most commonly prescribed treatment, but stopping it can trigger a surge in stomach acid known as rebound acid hypersecretion
• Gastrin levels increase during omeprazole treatment and can drive acid production higher than pre-treatment levels once the medication stops
• Ulcers can return to pre-treatment severity in as little as 3 days after the last dose
• Tapering omeprazole has not been shown to meaningfully reduce rebound risk
• Proactive management and gut support during the post-omeprazole window can help protect newly healed tissue

Quick Answer

Omeprazole works by blocking the stomach's acid-producing pumps. While it is highly effective at healing ulcers, stopping the medication can trigger a rebound effect where the body overproduces acid in response, exposing freshly healed stomach tissue to a surge in acidity. This is known as rebound acid hypersecretion, or RAHS. The critical window is the first 2 to 4 days after the last dose. Proactive management changes and targeted gut support during this period can make a meaningful difference in protecting the work that omeprazole started.

Why Omeprazole Works and Why Stopping It Gets Complicated

The horse's stomach is in a constant state of acid production. Unlike humans, who produce acid primarily in anticipation of a meal, horses are built to graze around the clock. Their stomachs produce hydrochloric acid continuously, regardless of whether there is food present to buffer it. When that buffering disappears, like during long gaps between feedings, stall confinement, or transport, the acid has nothing to work against except the stomach lining itself.

Omeprazole belongs to a class of drugs called proton pump inhibitors. It works by binding to the acid-producing pumps in the stomach wall and blocking the final step of hydrochloric acid production. It does not buffer acid. It does not coat the stomach. It shuts the pumps off at a systemic level, which is why it is so effective at giving ulcerated tissue the quiet environment it needs to heal.

The complication is what happens during treatment and immediately after.

When the stomach detects that acid levels have dropped, it responds by increasing production of a hormone called gastrin, which normally stimulates acid secretion. Gastrin levels rise during omeprazole treatment as the body tries to compensate for the suppressed acid. When the medication stops, those elevated gastrin levels drive acid production higher than it was before treatment began. That surge hits the stomach wall right at the moment when newly healed tissue is most vulnerable.

Research has demonstrated that gastrin levels begin rising within the first two weeks of omeprazole use and return to baseline within 2 to 4 days after discontinuation, confirming a short but critical window where horses are at elevated risk.³

How Quickly Can Ulcers Come Back?

The answer is faster than most people expect.

Research on Thoroughbred racehorses found that rebound gastric hyperacidity after discontinuing omeprazole, as a consequence of elevated gastrin levels, may contribute to the recurrence of equine squamous gastric disease within days to weeks of medication withdrawal. Some studies report ulcers returning to pre-treatment severity in as little as 3 days after the final dose.

That is not a reason to avoid omeprazole. It is a reason to be intentional about what comes after it.

Understanding the Two Regions of the Horse's Stomach

To understand why RAHS matters, it helps to know where ulcers typically form.

The horse's stomach has two distinct regions with very different levels of protection.

The squamous region sits in the upper portion of the stomach. It is lined with tissue similar to the esophagus and has no secretory glands, which means it has no built-in mechanism to protect itself from acid. This is where the vast majority of equine ulcers develop, particularly in performance horses where acid splashes upward during exercise and fast movement.

The glandular region occupies the lower portion of the stomach. It is lined with glands that produce acid, digestive enzymes, mucus, and bicarbonate. The mucus and bicarbonate act as a natural buffer, giving this region significantly more protection. Glandular ulcers do occur but are less common and require different management considerations.

When omeprazole treatment ends and acid surges, it is the squamous region that takes the hit first.

What Research Says About Tapering 

A common approach in human medicine is to taper proton pump inhibitors gradually rather than stopping abruptly, with the idea that a slower withdrawal reduces the rebound effect. In horses, the evidence does not support this approach.

Research indicates that tapering omeprazole when planning to discontinue the medication is unlikely to minimize rebound gastric hyperacidity in horses, at least for treatment durations of eight weeks and less. Tapering also increases cost without meaningful clinical benefit, making it a poor trade-off for most horse owners. 

The more evidence-backed strategy is to focus on management changes during and after omeprazole treatment, setting the horse up to protect its own stomach lining before the medication ends.

7 Management Strategies for the Post-Omeprazole Window

These are the habits that protect newly healed tissue and reduce the risk of rebound.

1. Keep Forage in Front of Them

Saliva is the horse's natural acid buffer. Chewing produces saliva, and saliva contains bicarbonate, which neutralizes stomach acid. A horse that has constant access to forage is constantly producing saliva, constantly buffering. An empty stomach has no buffer at all. This is the single most impactful zero-cost change you can make.

2. Add Alfalfa Before Exercise

Acid splash during exercise is one of the primary drivers of squamous ulcers. The physical motion of exercise throws stomach acid upward into the unprotected squamous region. Alfalfa is high in calcium and protein, both of which buffer acid and form a physical mat that helps prevent splashing. A small amount fed before riding or turnout provides meaningful protection during the highest-risk period of the day.

3. Feed Smaller, More Frequent Meals

Large grain meals dump a significant amount of starch into the digestive system at once. Excess starch that reaches the hindgut can disrupt microbial balance and increase acidity throughout the system. Smaller, more frequent meals keep the digestive load manageable and reduce the acid spikes that come with large single feedings.

4. Reduce Starch Where Possible

If your horse needs additional calories, consider healthy fats rather than increasing grain. Fat is a calorie-dense, low-starch energy source that does not drive the same acid response as starch-heavy feeds.

5. Minimize Stress During the Transition Period

The 48 hours following the last dose of omeprazole are a particularly vulnerable window. Where possible, reduce hauling, competition, and routine changes during this time. Stress elevates cortisol, which can compromise the stomach's protective mucus layer and increase acid secretion.

6. Prioritize Turnout and Social Interaction

Movement encourages gut motility. Social interaction reduces stress. Both have downstream effects on gastric health that are well established in equine research. These are not soft recommendations. They are part of the physiological foundation of a healthy digestive system.

7. Support the Gut Through the Transition

Research on Thoroughbred racehorses found that administration of a nutraceutical supplement during the post-omeprazole withholding period partially mitigated the prevalence of squamous ulceration recurrence, suggesting potential implications for horse welfare and performance during this critical transition window. 

Four Sixes Complete Gut Protection was formulated to support the full digestive system through exactly this kind of high-demand period. Prebiotics, probiotics, and postbiotics support hindgut microbial balance. Saccharomyces boulardii, the most researched probiotic yeast in equine medicine, helps maintain digestive stability during stress. L-glutamine provides fuel for the epithelial cells lining the gut wall, supporting barrier integrity when the system is under pressure. Oat beta glucan acts as a prebiotic to support beneficial bacterial populations and moderate starch transit. One scoop for maintenance. Two scoops during high-stress periods including the post-omeprazole window.

Actionable Checklist: Protecting Your Horse After Omeprazole 

• ✓ Keep forage available around the clock during and after treatment
• ✓ Feed a small amount of alfalfa before exercise to buffer acid splash
• ✓ Reduce grain meal size and increase feeding frequency
• ✓ Avoid hauling and major routine changes in the 48 hours after the last dose
• ✓ Maximize turnout and social interaction where possible
• ✓ Increase gut supplement support during the post-omeprazole transition
• ✓ Work with your veterinarian on a long-term management plan before starting treatment
• ✓ Address the root cause, not just the symptoms. If ulcers keep returning, something in the management program needs to change

Frequently Asked Questions

What is rebound acid hypersecretion in horses? Rebound acid hypersecretion, or RAHS, is an increase in stomach acid production that occurs after stopping omeprazole or other proton pump inhibitors. During treatment, the body compensates for suppressed acid levels by increasing production of gastrin, a hormone that stimulates acid secretion. When the medication stops, those elevated gastrin levels drive acid production higher than pre-treatment levels, creating a surge that can damage newly healed stomach tissue.

How quickly can ulcers return after stopping omeprazole? Research indicates ulcers can return to pre-treatment severity in as little as 3 days after the final dose. Gastrin levels typically return to baseline within 2 to 4 days, confirming that the highest-risk window is the first several days after discontinuation.

Does tapering omeprazole prevent rebound? Current equine research does not support tapering as an effective strategy for reducing RAHS in horses treated for 8 weeks or less. The more evidence-backed approach is to implement proactive management changes and gut support during and after treatment.

What is the difference between GastroGard and UlcerGard? Both contain omeprazole. GastroGard is a higher-dose, prescription-only product approved by the FDA for treating active gastric ulcers. UlcerGard is a lower-dose, over-the-counter product approved for prevention. Always work with your veterinarian to determine which is appropriate and for how long.

Why do horses produce stomach acid even when they are not eating? Horses evolved as continuous grazers. Their digestive systems are designed around constant forage intake, which means the stomach produces acid around the clock to support that feeding pattern. When modern management practices create gaps in forage access, that acid has nothing to buffer against except the stomach lining itself, which is the root cause of most squamous ulcers.

What is the squamous region and why does it matter? The squamous region is the upper portion of the horse's stomach. It is lined with tissue similar to the esophagus and has no glands to produce protective mucus or bicarbonate. This makes it the most vulnerable area of the stomach to acid damage, particularly during exercise when acid splashes upward, and during the rebound period after omeprazole is stopped.

Can gut supplements help prevent ulcer recurrence? Research supports the use of nutraceutical supplements during the post-omeprazole period to help reduce recurrence rates. Supplements that support microbial balance, gut barrier integrity, and the overall digestive environment can provide an additional layer of protection during the critical transition window after treatment ends.

How long should I increase gut support after stopping omeprazole? The highest-risk window is the first 2 to 4 days, but maintaining consistent gut support for several weeks following treatment is a reasonable approach, particularly for horses with a history of recurrent ulcers or those in high-stress environments like competition, hauling, or heavy training.

 

When to Call Your Veterinarian

Management goes a long way. But some situations require professional evaluation.
Contact your veterinarian if your horse shows recurring signs of ulcers after completing omeprazole treatment, including behavioral changes around feeding, girthiness, poor performance, weight loss, changes in manure, or colic episodes. Scoping is the only way to confirm whether ulcers are present and how severe they are. If ulcers keep coming back, it is a signal that something in the management program needs to be addressed, not just retreated.

The Takeaway

Omeprazole is a valuable tool. It is not a complete solution on its own.

The work of protecting your horse's stomach does not end when the treatment does. The days and weeks after the final dose are when the management habits you have built either hold the line or let it slip.

Know the window. Support the system. Do not let the work you put into treatment go to waste.

Shop Complete Gut Protection here.

We focus on the whole horse. The science. What works and stands the test of time, not chasing trends or quick fixes.

Formulated by veterinarians. Trusted on the ranch and in the arena. Built for horses that work.

-The 6666 Equine Supplements Team

 

References

1. Sykes BW, Hewetson M, Hepburn RJ, Luthersson N, Tamzali Y. European College of Equine Internal Medicine Consensus Statement: Equine Gastric Ulcer Syndrome in Adult Horses. J Vet Intern Med. 2015;29(5):1288-1299.

2. Clark B, Steel C, Vokes J, Shan JR, Gedye K, Lovett A, Sykes BW. Evaluation of the effects of medium-term omeprazole administration and of omeprazole discontinuation on serum gastrin and serum chromogranin A concentrations in the horse. J Vet Intern Med. 2023;37(4):1537-1543.

3. Shan R, Steel CM, Sykes B. The impact of two recommended withholding periods for omeprazole and the use of a nutraceutical supplement on recurrence of equine gastric ulcer syndrome in Thoroughbred racehorses. Animals (Basel). 2023;13(11):1823.