A study published on the 14th January 2026 has provided the first detailed insight into how the acid-suppressing drug vonoprazan behaves in the horse, raising important questions about future treatment options for equine gastric ulcer syndrome (EGUS), particularly in fed horses.
EGUS remains one of the most common and challenging conditions in performance and leisure horses alike. While omeprazole is widely used, its effectiveness can be limited by short duration of action in horses and the need for administration on an empty stomach, a requirement that can conflict with equine welfare and management realities.
Why vonoprazan matters
Vonoprazan belongs to a newer class of drugs known as potassium-competitive acid blockers (P-CABs). Unlike proton pump inhibitors such as omeprazole, P-CABs do not require activation in an acidic environment and are not significantly affected by the presence of food. In human medicine, these properties have translated into faster onset of action and more consistent acid suppression.
This study set out to determine whether similar advantages might exist in horses.
How the study was carried out
Researchers conducted a prospective, randomised crossover study using healthy Thoroughbred horses. Animals received:
- Vonoprazan at 0.5 mg/kg
- Vonoprazan at 1.0 mg/kg
- Omeprazole at 4 mg/kg
- Placebo (water)
Plasma drug concentrations were measured for up to 72 hours after dosing, and intragastric pH was continuously monitored before and after treatment. Importantly, horses were fed normally during the main study phase.
Key findings
- Vonoprazan was well tolerated, with no adverse effects observed at either dose.
- Absorption of vonoprazan was not affected by feeding, confirming a major theoretical advantage over omeprazole.
- At the higher dose (1 mg/kg), vonoprazan significantly increased the proportion of time gastric pH remained above 4 compared with placebo.
- Plasma concentrations exceeded those associated with effective acid suppression in other species.
- Drug exposure increased proportionally with dose, indicating predictable, linear pharmacokinetics.
In contrast, neither omeprazole nor the lower vonoprazan dose produced a statistically significant improvement in gastric pH under the fed conditions used in the study. The authors note that this likely reflects known limitations of single-dose omeprazole administration when horses are not fasted.
What this means for horses
Maintaining gastric pH above 4 for a sufficient proportion of time is considered important for ulcer healing. In this study, vonoprazan at 1 mg/kg achieved pH control consistent with thresholds associated with healing in both horses and humans.
Crucially, the ability to administer an effective acid suppressant without fasting could represent a meaningful welfare improvement, particularly for horses in training, hospitalised animals, or those prone to stress-related gastric disease.
Important limitations
The researchers emphasise that this was a small study involving healthy horses and a single dose of each treatment. Gastric ulcer presence was not confirmed endoscopically, and pH probe location within the stomach could not be standardised.
As a result, while the findings are promising, they should not yet be interpreted as evidence of clinical superiority or direct treatment guidance.
The bigger picture
This study provides an important first step in understanding vonoprazan in horses and supports further investigation, particularly longer-term dosing studies, work in horses with confirmed gastric disease, and research focusing on glandular ulceration.
For now, it reinforces a growing recognition within equine medicine that feeding status, pharmacology and welfare are inseparable considerations when managing gastric health.
What horse owners should take from this research
This study looks at a newer type of stomach acid–reducing medication and what it might mean for managing gastric ulcers in horses. Here are the key take-home points for owners, riders and yard managers.
1. Gastric ulcers remain common and complex
Equine gastric ulcer syndrome (EGUS) is widespread, especially in performance, competition and stabled horses. Treatment success depends on more than just medication – feeding, management, stress and turnout all play important roles.
2. Omeprazole has known limitations
Omeprazole is the most commonly used treatment, but:
- It works best when given on an empty stomach
- This often requires overnight or morning fasting, which is not natural for horses
- A single dose does not always give reliable acid suppression
This study reinforces why some horses respond well to omeprazole while others do not.
3. Vonoprazan may offer practical advantages
Vonoprazan belongs to a different drug group and, in this study:
- Worked even when horses were fed normally
- Raised stomach pH for longer at the higher dose tested
- Was well tolerated by all horses
For owners, this suggests a possible future option that may not require fasting before dosing.
4. Dose matters
Only the higher dose tested (1 mg/kg) produced a meaningful increase in stomach pH. Lower doses did not show the same effect. This highlights why “one-size-fits-all” dosing may not work for gastric treatments.
5. This is not a green light to change treatments yet
Important to know:
- This was a small study in healthy horses
- Horses did not have confirmed gastric ulcers
- Only a single dose was tested
Vonoprazan is not currently a licensed equine treatment in the UK, and more research is needed before it can be recommended routinely.
6. Management still matters as much as medication
Even the best drug cannot compensate for:
- Long periods without forage
- High-stress routines
- Limited turnout or social contact
Supporting stomach health still means prioritising ad-lib forage, fibre-based diets, consistent routines and minimising stress wherever possible.
7. Talk to your vet before making changes
If you suspect gastric ulcers or are managing a horse with ongoing gastric issues:
- Discuss diagnostic options such as gastroscopy
- Review feeding and management first
- Use medication only under veterinary guidance
The bottom line
This research is encouraging and points towards future treatments that may better fit normal horse management and welfare. For now, it adds to our understanding of why gastric ulcer treatment can be challenging – and why feeding, welfare and evidence-based decisions remain central to keeping horses comfortable and healthy.
