When Should You Give Omeprazole to a Horse With Ulcers?

By Dr Duncan Houston

Omeprazole is one of the most commonly used treatments for gastric ulcers in horses, but giving the right drug is only half the job.

The timing matters.

Many owners spend a lot of money on ulcer treatment and still feel as though their horse is not improving. The horse may still be girthy, picky with feed, dull in work, unsettled under saddle, or slow to gain condition. In some cases, the issue is not that omeprazole “doesn’t work.” It is that the horse may not be absorbing it properly.

For a medication that depends heavily on stomach conditions, feeding schedule, formulation, and disease type, small timing mistakes can make a big difference.

Quick Answer

Omeprazole is usually most effective when given early in the morning after an overnight period without feed, then followed by feed at least 30 minutes later. Giving omeprazole with hay or immediately around forage can reduce absorption and weaken acid suppression. Research in horses shows that diet and dose both affect omeprazole’s ability to raise stomach pH, with poorer acid suppression seen in horses on ad libitum hay compared with other study conditions. (PubMed)

Do not change your horse’s dose without your vet. The safer goal is to improve timing first, then reassess the horse’s response.

What Are Equine Gastric Ulcers?

Equine gastric ulcer syndrome, often shortened to EGUS, refers to ulceration or erosion in the horse’s stomach.

The horse’s stomach is not one uniform surface. It has different regions, and those regions behave differently. This is why two horses can both have “ulcers” but need different treatment plans.

The two main categories are:

Modern equine ulcer guidance separates squamous and glandular disease because their risk factors, biology, prevention, and treatment response are not the same. The EGGD consensus statement is especially clear that glandular disease should be considered distinct from squamous disease, and that prevention and treatment strategies for squamous ulcers cannot simply be copied across to glandular ulcers. (nbflaneshorse.com)

That distinction is clinically important. Squamous ulcers often respond well to acid suppression. Glandular ulcers can be more stubborn and may need a broader treatment plan.

Why Omeprazole Timing Matters

Omeprazole is a proton pump inhibitor. Its job is to reduce stomach acid production so the ulcerated stomach lining has a chance to heal.

In horses, omeprazole is not just swallowed and instantly active. It needs to be absorbed and then act on acid-producing cells. Food in the stomach, especially forage around dosing time, can interfere with how much active drug becomes available.

A 2017 study by Sykes and colleagues investigated how dose and diet affected acid suppression in horses. The study used six adult Thoroughbreds and compared two omeprazole doses under two dietary conditions. The researchers found that both dose and diet influenced intragastric pH, and that omeprazole’s ability to raise stomach pH was relatively poor under the hay diet condition compared with the high-grain, low-fibre study condition. (PubMed)

That does not mean high-grain feeding is good for ulcer horses. It is not the take-home message. The real lesson is that the feeding environment around omeprazole can change how well the medication works.

EquiManagement’s summary of Sykes’ work reported that ad libitum hay may reduce omeprazole bioavailability by 50 to 66 percent, and that horses given omeprazole after an overnight fast and then fed 60 to 90 minutes later achieved greater acid suppression than horses on unrestricted hay at dosing time. (EquiManagement)

In plain English: hay is good ulcer management overall, but hay at the wrong moment can make oral omeprazole less effective.

That is the awkward bit. Horses need forage, but omeprazole often needs a clear dosing window.

The Best Practical Omeprazole Schedule

The most useful routine for many horses is:

A practical example would be:

A 2023 review of equine gastric ulcer syndrome recommends giving omeprazole early in the morning after overnight fasting and at least 30 minutes before reintroducing feed. It also notes that omeprazole has superior bioavailability when given to fasted animals. (Research Portal)

Some vets prefer a 60-minute gap where practical. In a busy yard, 30 minutes may be more realistic. The most important point is not to give omeprazole buried in feed, mixed into a meal, or immediately after a hay net has been demolished.

Make Sure the Horse Actually Gets the Dose

This sounds obvious, but it is one of the easiest things to miss.

If paste ends up on the lips, teeth, stable wall, feed bucket, your sleeve, or the floor, the horse did not receive the full dose. The labelled directions for GastroGard advise making sure the horse’s mouth contains no feed and depositing the paste on the back of the tongue or deep into the cheek pouch, then briefly observing the horse to ensure the dose is not lost or rejected. (DailyMed)

In practice, I would check four things before deciding a horse is “not responding” to omeprazole:

1. Was it given on an empty enough stomach?

2. Was it followed by feed too quickly?

3. Was the whole dose swallowed?

4. Was the product appropriate, in date, and formulated for horses?

That last point matters. MSD Veterinary Manual notes that a specific equine product was developed because oral bioavailability of human or compounded omeprazole formulations can be poor in horses. (MSD Veterinary Manual)

Cheap omeprazole is not cheap if it does not work. Horses have a gift for turning false economy into a vet bill with hooves.

Squamous vs Glandular Ulcers: Why Response Can Differ

Omeprazole is particularly useful for squamous gastric disease because acid exposure is central to that problem. The aim is to suppress acid and keep stomach pH high enough to allow healing. MSD Veterinary Manual lists acid suppression and maintaining a stomach pH of 4 or above as primary treatment goals for equine squamous gastric ulcer disease. (MSD Veterinary Manual)

Glandular disease is trickier.

Glandular ulcers are not simply “too much acid.” They often involve impaired protective mechanisms in the stomach lining. Acid may worsen the injury and delay healing, but acid is not always the whole cause. That is why glandular ulcers may need longer treatment, different medication combinations, management changes, rest days, careful NSAID review, or repeat gastroscopy. MSD notes that glandular disease may require 45 to 60 days of treatment and that repeat gastroscopy can guide treatment duration. (MSD Veterinary Manual)

So, if a horse is not improving, do not jump straight to “omeprazole resistance.” More often, the issue is one of these:

• The ulcer type is glandular rather than squamous

• The dosing timing is poor

• The medication is being given with feed

• The horse is not receiving the full dose

• The formulation is not reliable

• Stress, training, travel, or NSAID use is still driving the problem

• The horse has another condition that looks like ulcers

How Worried Should You Be If Omeprazole Is Not Working?

A horse that does not improve on omeprazole deserves a structured rethink, not guesswork.

The real concern is not just that the horse is still uncomfortable. It is that the original diagnosis, ulcer location, dosing method, or management plan may need changing.

When Is This an Emergency?

Most adult horses with gastric ulcers are not emergency cases, but some situations should not wait.

Call a vet urgently if your horse has:

• Colic signs

• Repeated lying down or rolling

• Severe depression

• Complete refusal to eat

• Signs of dehydration

• Fever

• Black, tarry, or bloody manure

• Persistent pain

• Rapid weight loss

• Worsening signs despite treatment

• Any ulcer signs in a foal

Foals are a special concern. Merck Veterinary Manual notes that ulcer complications are most frequent and severe in foals, including stomach perforation and reflux-like complications. (Merck Veterinary Manual)

If a foal looks dull, painful, bloated, salivates excessively, grinds teeth, lies down repeatedly, or stops nursing, do not monitor at home. That is a vet call now.

What Should You Do Next?

If your horse is currently on omeprazole, the next step is not to panic. It is to tighten the process.

1. Confirm the diagnosis

Gastroscopy remains the definitive way to diagnose gastric ulcers. UC Davis explains that gastric ulcers can only be definitively diagnosed by gastroscopy, which allows the vet to examine the stomach surface directly. (Center for Equine Health)

Clinical signs can suggest ulcers, but they are not specific. A horse can be girthy, sharp, poor in work, or picky with feed for many reasons.

2. Confirm the ulcer type

Ask whether the ulcers are squamous, glandular, or both. This changes expectations.

Squamous disease often responds better to omeprazole alone. Glandular disease may need a longer or broader plan.

3. Fix the timing before changing the dose

Before increasing the dose, changing products, or adding medications, check whether the current medication is being given correctly.

A good rule:

Omeprazole first. Feed later. Forage through the day.

4. Do not reduce the dose yourself

Better absorption may improve results and may eventually reduce unnecessary cost, but that does not mean owners should lower the dose without veterinary guidance.

The labelled treatment dose for GastroGard is once daily for four weeks at 4 mg/kg, with a lower maintenance dose used for prevention of recurrence. (DailyMed)

Dose decisions depend on the product, horse, ulcer location, severity, response, and country-specific prescribing rules.

5. Review the whole management picture

Medication can help ulcers heal, but management decides whether they come back.

Look at:

• Forage access

• Long gaps without feed

• Concentrate and starch intake

• Training intensity

• Travel

• Competition stress

• Turnout

• Social stress

• NSAID use

• Recent yard changes

• Pain from other conditions

MSD lists intense exercise, dietary factors, high concentrate diets, and periods of food restriction as ulcer risk factors in horses. (MSD Veterinary Manual)

What If Your Horse Is Also on Sucralfate?

Sucralfate is sometimes used, especially when glandular ulcers are suspected or confirmed. It acts more as a mucosal protectant than an acid suppressant.

Timing still matters.

UC Davis notes that sucralfate may be added in some severe cases but should not be given at the same time of day as omeprazole. (Center for Equine Health)

Do not stack every ulcer medication into one morning paste session unless your vet has specifically planned it that way. The schedule may need spacing so one medication does not interfere with another.

Common Mistakes Owners Make With Omeprazole

Giving it with breakfast

This is the classic mistake. If omeprazole is mixed into feed or given when the horse has just eaten hay, absorption may be reduced.

Leaving ad lib hay right up to dosing time

Forage is important, but constant hay access immediately before oral omeprazole can undermine treatment. The answer is not starving the horse. The answer is a controlled dosing window.

Using unreliable formulations

Human omeprazole capsules, crushed tablets, or poorly made compounded products may not behave like licensed equine formulations.

Stopping too early

Owners often stop when the horse seems better. Ulcers may not be fully healed yet. UC Davis recommends a full month of treatment followed by recheck endoscopy to confirm healing in diagnosed cases. (Center for Equine Health)

Treating ulcers while ignoring stress

A horse in hard work, frequent travel, social stress, limited turnout, or ongoing pain may relapse even after appropriate medication.

Assuming every girthy horse has ulcers

Ulcers are common, but they are not the only cause of girthiness or poor performance. Saddle fit, back pain, lameness, ovarian pain, dental disease, hindgut disease, parasites, and training stress can all confuse the picture.

Can Better Timing Lower the Cost?

Potentially, but indirectly.

Correct timing can help you get better value from the dose you are already giving. It may reduce wasted medication, avoid unnecessary treatment escalation, and improve the chance that a properly diagnosed ulcer actually heals.

But it does not mean every horse can be treated at a lower dose.

The sensible order is:

1. Diagnose properly

2. Use an appropriate equine formulation

3. Give it correctly

4. Recheck response

5. Adjust only with veterinary guidance

That is how you save money without gambling with the horse.

How To Reduce Ulcer Recurrence

Medication helps heal ulcers. Management helps stop them returning.

Useful prevention strategies include:

• Keep forage available through most of the day

• Avoid long fasting periods

• Reduce large grain meals

• Feed more frequent smaller meals where needed

• Consider some alfalfa before exercise if appropriate

• Increase turnout where possible

• Reduce unnecessary travel stress

• Avoid sudden feed and routine changes

• Use NSAIDs carefully and only as advised

• Build in rest days for hard-working horses

• Recheck horses that relapse quickly

UC Davis lists frequent or free-choice forage, reduced grain and concentrates, turnout, reduced training intensity, minimized fasting, and careful anti-inflammatory use as part of ulcer prevention and management. (Center for Equine Health)

For glandular disease, rest days can matter. EquiManagement’s summary of Sykes’ recommendations notes that horses exercised six to seven days per week were more likely to develop glandular disease than horses exercised five or fewer days per week, and that providing at least two rest days may support healing in glandular disease. (EquiManagement)

FAQs About Omeprazole Timing in Horses

Can I give omeprazole with feed?

Ideally, no. Omeprazole is usually best given before feed, after an overnight feed-free window, then followed by feed at least 30 minutes later. Giving it with hay or a meal may reduce absorption.

How long should I wait before feeding after omeprazole?

A minimum of 30 minutes is commonly recommended. Many vets aim for 60 minutes when practical. Your vet may adjust this depending on your horse, yard routine, ulcer type, and other medications.

Should a horse with ulcers be fasted overnight?

A short overnight dosing window can help omeprazole absorption, but prolonged fasting is not good ulcer management. The aim is not to leave the horse hungry for long periods. The aim is to create a practical medication window, then maintain good forage access through the day.

Why is my horse still showing ulcer signs on omeprazole?

Possible reasons include poor timing, incomplete dosing, unreliable formulation, glandular ulcers, ongoing stress, NSAID use, insufficient treatment duration, or another condition mimicking ulcers.

Can I use human omeprazole for my horse?

Do not substitute human omeprazole without veterinary direction. Horses absorb omeprazole differently, and equine-specific formulations are designed for this problem. Poor formulation choice can lead to poor treatment response.

Final Thoughts

Omeprazole can be an excellent treatment for equine gastric ulcers, but it is not magic paste. It works best when the diagnosis is right, the formulation is appropriate, the dose is swallowed properly, and the timing around feeding is planned.

The key message is simple:

Give omeprazole before feed, not with feed.

For many horses, the best routine is early morning dosing after an overnight feed-free window, followed by forage 30 to 60 minutes later. Then the rest of the day should return to good ulcer-safe management: forage, routine, turnout, lower stress, careful exercise planning, and sensible medication use.

If your horse is not improving, do not just increase the dose or switch products blindly. Recheck the timing, confirm the ulcer type, review the management, and involve your vet before changing the plan.

If you are unsure whether your horse’s ulcer plan is being timed correctly, or signs are not improving as expected, ASK A VET™ can help you work through the next safest step.