We asked the leading veterinarians behind Four Sixes Equine Supplements your most asked questions about common medications that your horses are on.
Key Takeaways
- NSAIDs like phenylbutazone block the same prostaglandins that protect the stomach and hindgut lining, not just the ones driving pain and inflammation
- Research has shown that all horses treated with phenylbutazone developed grade 2 or higher glandular ulceration, while untreated horses did not¹
- Furosemide causes significant losses of sodium, chloride, calcium, potassium, and magnesium, with calcium loss documented for up to 72 hours after a single dose²
- Long-term omeprazole use has been shown to decrease calcium digestibility in horses by up to 20%³
- When omeprazole is stopped, acid production can surge higher than pre-treatment levels, exposing newly healed tissue fast
- Building a strong gut foundation proactively reduces how often you need these tools and how hard the trade-off hits when you do
Quick Answer
Bute, Lasix, and omeprazole are legitimate tools. Used appropriately, they do their jobs. The issue is that each one, particularly when used long term or in combination, quietly works against the digestive system that keeps everything else running. Understanding what is happening inside the gut when these medications are on board is the first step toward protecting your horse while still using the tools that work.
We Hear This Every Week
A horse comes up sore. You reach for the bute. The mare is working hard in the heat. You add Lasix. The stomach looks off, so you pull out the omeprazole.
These are tools. Good ones, in the right situations.
But what most people do not realize is that when you use them, especially long term or in combination, they come with a trade-off that quietly works against the very horse you are trying to protect.
We put your most common questions to Dr. Rob Franklin, board-certified equine internal medicine specialist and one of the veterinarians behind the 6666 Equine Supplements formulas. Here is what he had to say.
What Is Bute Actually Doing to My Horse's Gut?
Phenylbutazone, banamine, and other NSAIDs block prostaglandins. That is how they reduce pain and inflammation. The problem is that prostaglandins also do something else entirely: they protect the stomach and hindgut lining by supporting blood flow, mucus production, and cellular turnover.
When you block prostaglandins to manage pain, you are simultaneously reducing the protection those prostaglandins provide to the gut wall.
As Dr. Franklin explains it, bute and cortisol work on the body in essentially the same way. Both suppress those protective prostaglandins. One the body makes itself under stress. The other you give through a syringe or a tube.
Research has confirmed this directly: all horses treated with phenylbutazone developed grade 2 or higher glandular ulceration, while untreated horses did not.¹ And it is not just the stomach. NSAID use in horses is also associated with right dorsal colitis, a serious condition affecting the right dorsal colon that can lead to protein loss and significant systemic consequences.
You are giving your horse something to feel better and at the same time quietly eroding the lining of the digestive system that keeps everything else running.
What Does Lasix Add to the Equation?
Lasix is a diuretic. It pulls fluid out of the body, which is the point when managing exercise-induced pulmonary hemorrhage. But along with that fluid go electrolytes and not just a few.
Research has documented that furosemide treatment results in decreases in plasma potassium, chloride, and calcium concentrations persisting for the full eight-hour observation period after administration.² Sodium and chloride losses in the first four hours can be 40 to 50 times higher than normal. Calcium loss has been documented for up to 72 hours after a single dose.
Now layer that on top of long-term omeprazole, which suppresses the stomach acid needed to properly absorb calcium from the diet.
As Dr. Franklin put it plainly: "If you do that and you impair the ability to digest calcium in the diet, now you've got a horse that cramps and has poor bones. Not a good combination for an elite athlete."
Replacing what Lasix removes is not optional for a horse at any level of work. It is a requirement.
What Is Long-Term Omeprazole Doing That Most People Miss?
Omeprazole has its place. It is a critical part of treating and healing gastric ulcers. But staying on it indefinitely without addressing the root cause creates its own set of problems.
Stomach acid is not just there to cause ulcers. It sterilizes the digestive tract, breaks down protein for muscle repair and recovery, and helps the body absorb calcium for bone health. When you suppress it chronically, you leave gaps in all three of those functions.
Recent research on long-term omeprazole use in horses has highlighted the potential for rebound gastric hyperacidity at discontinuation, decreased calcium absorption during administration, and disruption to hindgut function when used alongside NSAIDs.³
A digestibility trial documented that two weeks of omeprazole administration decreased calcium digestibility by up to 20%. For a performance horse already losing calcium through Lasix, that compounding effect matters.
And when you stop? The rebound is real.
As Dr. Keith Latson describes it: "It does not take long for that fire just to reignite in those horses."
So What Do These Three Look Like Together?
Each medication has a legitimate role. The concern is what happens when they are used together or long term without proactive gut support underneath.
NSAIDs compromise the protective lining of the gut. Lasix strips the electrolytes and minerals the body needs to function and recover. Long-term omeprazole reduces the stomach's ability to absorb the calcium being lost through Lasix in the first place. Layer in stress, hauling, competition, and empty stomach time, and the foundation underneath the horse starts to crack quietly before anything shows up clinically.
Causes vs. Effects: Quick Reference
| Medication | Primary Job | Gut Trade-Off |
|---|---|---|
| Phenylbutazone / NSAIDs | Reduce pain and inflammation | Blocks prostaglandins that protect the stomach and hindgut lining |
| Lasix / Furosemide | Reduce pulmonary bleeding | Significant losses of sodium, chloride, calcium, potassium, and magnesium |
| Omeprazole | Suppress acid to heal ulcers | Reduces calcium absorption, disrupts hindgut when used with NSAIDs, rebound hyperacidity on stopping |
8 Ways to Protect the Gut When These Medications Are in the Program
The goal is not to stop using the tools that work. It is to build a foundation strong enough that you need them less often, and that your horse can hold up when you do.
1. Keep Forage in Front of Them Constantly
The fiber mat in the stomach is one of the most underappreciated protective mechanisms a horse has. Chewing produces saliva, saliva contains bicarbonate, and bicarbonate buffers acid. An empty stomach is an exposed one. This is the single most impactful zero-cost habit you can maintain.
2. Add Alfalfa Before Exercise
Alfalfa is high in calcium and protein, both of which buffer stomach acid and help protect the unprotected squamous region from acid splash during movement. A small feeding before exercise provides meaningful protection during the highest-risk window of the day.
3. Split Grain Into Smaller, More Frequent Meals
Large grain meals dump a significant amount of starch into the digestive system at once. Excess starch reaching the hindgut disrupts microbial balance and drives up acidity. Smaller, more frequent meals reduce that load and the acid spikes that come with single large feedings.
4. Limit NSAIDs to the Lowest Effective Dose for the Shortest Time Necessary
Work with your veterinarian on whether a newer generation anti-inflammatory with better gastrointestinal tolerability is appropriate for your horse. When NSAIDs are necessary, concurrent gut support is not optional.
5. Replace Electrolytes Comprehensively When Lasix Is in the Program
Replacing what Lasix removes is not optional for an elite athlete. A comprehensive electrolyte approach covering sodium, chloride, calcium, potassium, and magnesium is part of responsible management for any horse on furosemide.
6. Address Root Causes Rather Than Staying on Omeprazole Indefinitely
Work with your veterinarian to identify and address the management factors driving ulcer recurrence: forage access, feeding schedule, stress, and competition demands. Omeprazole is most effective as a treatment tool, not a permanent strategy.
7. Support the Gut Proactively Before the Problem Shows Up
As Dr. Franklin says, if you are waiting until the horse gets cinchy, loses weight, or has loose manure, you are already behind. Gut support before the fire starts is more effective and less costly than treating the fire after it is burning.
8. Use a Full Gut Support Formula That Covers Both Stomach and Hindgut
6666 Complete Gut Protection supports both the stomach and hindgut in a single formula. Beta-glucans and L-glutamine protect and nourish the stomach lining. Prebiotics, probiotics, and postbiotics support the microbial balance and fermentation environment in the hindgut. The postbiotic in the formula has also been shown in research to reduce inflammatory markers measured directly in the joint, which matters when the gut and joint are communicating through the same inflammatory pathways that NSAIDs are also affecting. One scoop for maintenance. Two scoops during high-demand periods including NSAID use, hauling, and competition.
Actionable Checklist: Managing Gut Health When Medications Are in the Program
- ✓ Keep forage available at all times, especially when NSAIDs are being used
- ✓ Feed small amounts of alfalfa before exercise to buffer acid splash
- ✓ Split grain into smaller, more frequent meals to reduce hindgut starch load
- ✓ Use NSAIDs at the lowest effective dose for the shortest time necessary
- ✓ Replace electrolytes comprehensively any time Lasix is administered
- ✓ Avoid long-term omeprazole without addressing the root cause with your veterinarian
- ✓ Start gut support before problems appear, not after
- ✓ Increase gut supplement dosing during periods of NSAID use, hauling, and competition
- ✓ Know your horse's baseline so you catch changes early
- ✓ Work with your veterinarian to build a program tailored to your horse's specific demands
Frequently Asked Questions
Is it dangerous to use bute, Lasix, and omeprazole at the same time?
Each medication has legitimate uses. The concern is the cumulative effect on the gut when they are used together or long term without proactive support. NSAIDs compromise the protective lining. Lasix depletes minerals including calcium. Long-term omeprazole reduces the ability to absorb that calcium. Used in combination without gut support, these effects compound. Work with your veterinarian and support the gut proactively when any of these medications are in the program.
How quickly does bute cause gut damage in horses?
Research has shown that all horses treated with phenylbutazone at the maximum recommended dosage developed grade 2 or higher glandular ulceration within the study period.¹ This does not mean bute should never be used. It means gut protection should be in place any time it is.
How long does calcium loss last after a Lasix dose?
Research has documented calcium loss for up to 72 hours after a single furosemide dose.² For horses on regular Lasix programs, this represents a sustained drain on calcium availability that compounds with any reduction in calcium absorption from long-term omeprazole use.
Does omeprazole affect more than just stomach acid?
Yes. Long-term use has been associated with decreased calcium digestibility, potential disruption to hindgut function particularly when used alongside NSAIDs, and rebound acid hypersecretion when discontinued.³ Stomach acid is necessary for sterilizing the digestive tract, breaking down protein, and absorbing calcium. When chronically suppressed, all three of those functions are impaired.
What is the rebound effect when stopping omeprazole?
When omeprazole is stopped, the acid-producing cells that have been suppressed respond by producing more acid than before treatment began. This surge hits newly healed stomach tissue at its most vulnerable point. As Dr. Franklin explains it, "It does not take long for that fire just to reignite in those horses." Work with your veterinarian on a plan that includes proactive management and gut support during the transition window.
What is the gut-joint connection and why does it matter here?
The gut is where a significant portion of the body's immune and inflammatory signaling originates. When gut health is disrupted, those inflammatory signals ripple systemically, including to joint tissues. NSAIDs affect those same inflammatory pathways. Supporting the gut helps maintain a healthier overall inflammatory environment, which matters for joints, recovery, and long-term soundness.
How do I know if my horse's gut is struggling?
Common early signs include behavioral changes around feeding or girthing, changes in manure consistency, unexplained weight loss, poor coat condition, and subtle shifts in performance or attitude. By the time signs are obvious, the problem has usually been building for a while. Proactive management and regular veterinary evaluation are the most effective approach.
When to Call Your Veterinarian
Contact your veterinarian if your horse shows signs of gut distress while on any of these medications, including recurring colic, changes in manure, behavioral changes around feeding or girthing, unexplained weight loss, or poor performance. Scoping is the only way to confirm whether gastric ulcers are present. If ulcers keep returning despite treatment, something in the management program needs to change, not just be retreated.
The Takeaway
Know what your tools cost.
Bute, Lasix, and omeprazole earn their place in performance horse management. But each one asks something of the gut in return. Building a strong foundation through consistent management, forage access, electrolyte support, and targeted gut supplementation is what allows your horse to hold up when the demands are highest.
Protect the system that makes everything else possible.
Support the gut before the fire starts.
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
- Pedersen SK, Cribb AE, Read EK, French D, Banse HE. Phenylbutazone induces equine glandular gastric disease without decreasing prostaglandin E2 concentrations. J Vet Pharmacol Ther. 2018;41(2):239-245.
- Freestone JF, Carlson GP, Harrold DR, Church G. Influence of furosemide treatment on fluid and electrolyte balance in horses. Am J Vet Res. 1988;49(11):1899-1902.
- Sykes BW. A free ride: is long-term omeprazole therapy safe and effective? Equine Vet Educ. 2021;33(10):556-560.
