Bute for Horses (Phenylbutazone): Safe Use, Risks, and Show-Rule Basics
- Horse Education Online
- 2 days ago
- 16 min read
Bute for horses (phenylbutazone) is one of the most widely used pain and inflammation medications in the horse world. It can make a stiff, sore horse noticeably more comfortable, especially with arthritis, soft-tissue strains, or post-work soreness.
At the same time, bute is not a harmless barn painkiller. It can mask important warning signs like fever, colic pain, and serious lameness, and it carries real risks for the stomach, colon, and kidneys when the dose, duration, or horse’s condition are not carefully managed.
This guide is written for owners, riders, and barn managers who want to use bute safely under veterinary direction, understand where it fits compared with Banamine and Equioxx, and avoid using it in situations where it could do more harm than good.
Disclaimer: This article is for general education only and is not veterinary advice. Phenylbutazone is a prescription drug; never start, stop, or change any dose without your veterinarian, and always treat colic, fever, neurologic signs, and non–weight-bearing lameness as emergencies that need direct veterinary care.
TL;DR: Bute for Horses
What it is: Bute (phenylbutazone) is a prescription NSAID for horses. It reduces pain and inflammation but can also mask serious problems and damage the gut and kidneys if misused.
Okay with a vet’s plan: Short-term relief for known musculoskeletal pain (arthritis flare, post-show soreness, diagnosed soft-tissue strain) with clear dose, duration, and monitoring.
Never as a “cover-up”: Do not use bute to push through fever, colic signs, neurological signs, non–weight-bearing lameness, dehydration, diarrhea, or known ulcers/kidney disease. Call your vet instead.
Risks to watch: Reduced appetite, manure changes, diarrhea, recurring mild colic, darker manure, less or darker urine, dullness. Stop bute and call your vet if any of these appear.
Other options: Banamine is usually for colic and eye pain; Equioxx is often for long-term arthritis. None of them fix the underlying cause without good hoof care, footing, workload, and nutrition.
Competition horses: USEF/EC/FEI treat bute as a regulated competition medication with thresholds and one-NSAID rules. Always follow your current rulebook and build a withdrawal plan with your vet.
What Bute Is (and Isn’t)
Definition
Bute is the common barn name for phenylbutazone, a prescription nonsteroidal anti-inflammatory drug (NSAID) used in horses.
In simple terms, bute:
Reduces pain
Reduces inflammation
Can help reduce fever
It is widely used for short-term relief of pain and inflammation from musculoskeletal problems such as lameness, arthritis, tendon or ligament strain, and overuse injuries. In many countries, bute is legally for veterinary use only and can only be dispensed with a prescription from a licensed veterinarian
How bute works in the body (in simple terms)
Inside the body, bute works by blocking enzymes called cyclo-oxygenase (COX-1 and COX-2). These enzymes help make substances called prostaglandins, which are involved in pain, fever, and inflammation.
When bute reduces prostaglandin production:
Pain signals are less intense
Inflammatory swelling can go down
Fever may decrease
This is why bute is so effective for sore joints, tendons, and ligaments, and why it has been one of the most commonly prescribed NSAIDs in horses for decades.
However, prostaglandins also help protect the stomach, intestines, and kidneys. When those protective prostaglandins are reduced for too long, or at too high a dose, bute can damage the gastrointestinal tract and kidneys, especially in dehydrated or already-ill horses.
What bute does and what it does not do
To keep decisions clear at barn level, it helps to separate what bute can do from what it cannot do:
What bute does | What bute does not do |
Reduces pain from many musculoskeletal problems (lameness, arthritis, strains) | Does not heal torn ligaments, fractures, or joint disease on its own |
Lowers inflammation and heat in affected tissues | Does not tell you why your horse is lame or sore |
Can help reduce fever as part of a vet-directed treatment plan | Should not be used to “hide” a fever so the horse can still work or travel |
Improves comfort so the horse can move more easily | Can mask signs that a condition is getting worse, delaying diagnosis |
Under vet direction, may be part of a long-term management plan for some horses | Is not a harmless “painkiller” you can give freely without dose or duration limits |
Why “masking” matters
Because bute makes a horse feel better, the horse may:
Walk more soundly than they truly are
Look less colicky
Seem less “off” than they really feel
In the short term, this can trick owners into thinking the problem is minor or improving, when the disease process is still active underneath. This is one reason why prolonged or unsupervised use of phenylbutazone has been linked with serious complications such as right dorsal colitis (a potentially life-threatening colon inflammation) and kidney injury, especially in dehydrated or stressed horses.
This is also why organizations like USEF, FEI, and national federations regulate how and when NSAIDs like bute can be used in competition horses: they want to balance legitimate pain control with horse welfare and fair play.
When Bute May Be Appropriate (Owner-Safe Scenarios)
Used correctly and under veterinary guidance, bute for horses can be a helpful part of short-term pain management. The key ideas are: you know the cause, you have a plan with your vet, and you track how your horse responds.
1. Known, Short-Term Musculoskeletal Soreness
Examples where your vet may approve phenylbutazone for horses:
A known hard workout or show that has left your horse mildly “stiff but bright,” with normal appetite, normal manure, and no fever
A diagnosed soft-tissue strain or mild tendon/ligament injury where your vet has already examined the horse and outlined a rest and rehab plan
Chronic, documented arthritis in an older horse where your vet has recommended bute for short bursts, such as during weather changes or brief flare-ups
In these scenarios, bute is usually one part of a program that also includes:
Controlled exercise or stall rest
Hoof balance and footing management
Weight management and appropriate nutrition
A clear re-check plan with your veterinarian
2. Always Inside a Vet-Directed Plan
For most horses, a safe framework looks like this:
Diagnosis first, then medication
Clear dosing instructions from your vet
Defined duration (for example, a few days for a mild flare-up, not weeks on end)
If your vet has given you a written or verbal plan, keep it with your barn records and write down:
What to record | Why it matters |
Date and time of each dose | Helps your vet see patterns and prevent stacking or overdosing |
Amount and form (paste, powder) | Confirms what was actually given |
Reason for giving (e.g., “post-show soreness, LF fetlock arthritis”) | Links the medication to the underlying problem |
Horse’s vital signs before first dose | Shows whether your horse was already running a fever or abnormal vitals |
Changes in behaviour or comfort | Helps identify whether bute is helping, not changing anything, or causing issues |
You can use these vitals tools as your baseline:
Heart rate guide: Average heart rate for a horse: what’s normal and how to check it
Full vitals reference: The horse’s vital signs
3. “Mild, Known, and Improving” Rule of Thumb
A practical way to think about owner-safe use of horse pain medication under vet guidance:
Mild: soreness is noticeable but your horse still walks willingly, eats, drinks, and passes normal manure.
Known: you and your vet understand the likely cause (for example, a documented arthritic joint, a recent overuse event).
Improving: over 24–48 hours, your horse looks better, not worse, on the same or a reduced dose.
If, instead, your horse’s pain stays the same or worsens, or new signs appear (fever, colic, neurologic changes), that’s a stop-and-call-your-vet moment, not a “give more bute” moment.
When Not to Give Bute
There are situations where giving bute for horses can hide crucial signs, increase the risk of complications, or go against your sport’s welfare rules. In these settings, your safest move is: do not give bute; call your vet.
1. Fever, Systemic Illness, or “Sick Horse” Signs
Do not reach for phenylbutazone if:
Your horse feels hot or you suspect a fever
You see reduced appetite, dullness, or changes in manure
Your horse is breathing harder at rest, or has a fast heart rate at rest
Bute can temporarily lower a fever and make a sick horse look “better,” while the infection or disease continues unchecked.
Instead:
Take a temperature and heart rate
Compare with:
Call your veterinarian with exact numbers and a description of your horse’s behaviour.
2. Colic or Suspected Colic
Using bute as a “colic painkiller” at home is risky because:
It can mask pain and make a serious colic look mild
It can delay your decision to get urgent veterinary care
Some colic types already compromise blood flow to the gut, and NSAIDs add extra strain on the intestinal lining and kidneys
If you suspect colic:
Do not give bute unless your veterinarian instructs you to
Start your first-hour checklist from:
3. Neurological Signs or Unusual Gait Changes
Avoid bute and call your vet if you notice:
Stumbling or “drunk” movement
One hind leg that does not track or place normally
Sudden, unexplained weakness or toe dragging
Asymmetrical facial muscles or odd eye position
These can be early signs of neurological disease such as equine protozoal myeloencephalitis (EPM), cervical spinal problems, or other serious conditions. Masking discomfort with bute may delay imaging, testing, and targeted treatment.
For a focused review of EPM red flags, keep this handy: EPM in horses: early signs, diagnosis, management
4. Dehydration, Poor Drinking, Heat Stress, or Diarrhea
Bute is harder on the kidneys and gut when:
Your horse is dehydrated
It is very hot and humid and your horse is sweating a lot
Manure is loose or diarrhea has started
Your horse is not drinking normally
Dehydration reduces blood flow to the kidneys and intestine. Adding an NSAID on top of that can tip a stressed system into kidney damage or right dorsal colitis, both of which can be life-threatening.
Use these resources to check hydration and electrolyte status before any NSAID use:
5. Known Ulcers, Kidney Disease, or High-Risk Horses
Use extreme caution and veterinary supervision (often with alternative medications) in horses with:
Documented gastric ulcers or a history of right dorsal colitis
Known or suspected kidney disease
Long-term high-dose NSAID use in the past
Seniors with multiple health conditions
Pregnant mares, where risk-benefit assessment is more complex
In many of these horses, your vet may recommend:
A different NSAID (for example, a COX-2–selective drug)
A lower dose with strict monitoring
Or avoiding NSAIDs altogether in favour of other pain-management strategies
6. Stacking NSAIDs or Combining with Steroids
One of the most important safety rules:
Do not combine bute with other NSAIDs or with corticosteroids unless your veterinarian has explicitly directed it and is closely monitoring your horse.
Common combinations to avoid without strict vet oversight:
Bute + flunixin (Banamine)
Bute + firocoxib (Equioxx)
Bute + aspirin or other NSAIDs
Bute + systemic corticosteroids (for example, dexamethasone)
Stacking NSAIDs dramatically increases the risk of gastric and colon ulceration and kidney injury.
7. Quick “Do Not Give Bute” Reference Table
You can print or bookmark this table and keep it with your barn records:
Situation | Give bute at home? | Safer step |
Fever of unknown cause | No | Check temperature and heart rate; call your vet |
Suspected colic | No (unless vet directs) | Follow colic first-hour checklist and call your vet |
Neurological signs (stumbling, unusual gait, facial asymmetry) | No | Remove from work, keep safe, call your vet |
Not drinking well, heat stress, or diarrhea | No | Check dehydration, offer water/electrolytes, call your vet |
Known ulcers or kidney disease | Only if vet says so | Discuss alternative plans or closely supervised NSAID use |
Already on another NSAID or steroids | No | Call your vet before adding anything |
Mild post-exercise stiffness in a bright, eating horse with normal vitals and a vet-diagnosed condition | Possibly (if vet has already provided a plan) | Follow the vet’s specific dosing and monitoring instructions |
Side Effects and Risks (What Owners Actually See)
All NSAIDs carry risks for the gut and kidneys. For phenylbutazone, these risks are well documented in research and clinical reports.
The three big categories:
Gastrointestinal (mouth, stomach, small intestine, colon)
Kidneys (renal function)
Blood proteins and systemic effects in cases like right dorsal colitis
1. Gastrointestinal Side Effects
Commonly reported or documented GI issues from bute misuse or sensitivity include:
Mouth or stomach ulcers (drooling, reluctance to eat, mild colic signs)
Right dorsal colitis (RDC) – an ulcerative disease of the right dorsal colon
Diarrhea, sometimes with soft or watery manure
Colic episodes (mild to severe)
Black, tarry, or very dark manure (suggesting bleeding higher in the GI tract)
Right dorsal colitis is strongly associated with phenylbutazone in multiple studies. Horses may show:
Lethargy and dullness
Colic signs
Diarrhea
Low blood protein (hypoproteinemia, hypoalbuminemia)
Thickened right dorsal colon on ultrasound
2. Kidney (Renal) Risks
Phenylbutazone can reduce blood flow to the kidneys, especially in:
Dehydrated horses
Horses with low blood volume (for example, from diarrhea or blood loss)
Horses with pre-existing kidney disease
Foals and very young horses
Signs that may point toward kidney issues:
Reduced urine output
Dark, concentrated urine
Lethargy and reduced appetite
Worsening dehydration even with water available
This is why every bute decision should be paired with:
Honest assessment of hydration status
Good salt and electrolyte management in hot conditions or heavy work:
3. Risk Multipliers (Situations That Make Bute More Dangerous)
Research and clinical experience highlight several “risk multipliers” that increase the likelihood of serious side effects:
High doses (especially above label guidelines)
Long duration (many days or weeks without veterinary oversight)
Stacking NSAIDs (bute plus flunixin, ketoprofen, etc.)
Combining with corticosteroids (dexamethasone, prednisolone)
Dehydration, heat stress, or diarrhea
Pre-existing GI or kidney disease
Pregnant mares and neonates, where safety margins are narrower.
Learn more by reading Equine NSAIDs and Analgesics
What an Owner Might Actually Notice
Here is a practical “what I see in the barn” list linked to possible bute-related issues:
What you observe | Possible concern |
Your horse eats less or leaves grain after starting bute | Stomach discomfort or early ulcers |
Softer manure, progressing to diarrhea | GI irritation, possible colitis |
Mild recurring colic episodes after several days of bute | Right dorsal colitis or generalized GI upset |
Duller attitude, slower to move, not themselves | Systemic effects, pain, or GI/kidney complications |
Darker gums, increased heart rate, cool extremities | Dehydration, shock, systemic disease – emergency |
Less urine, darker urine, drinking less | Possible kidney stress or dehydration |
Any of these patterns, especially if they appear after starting or increasing phenylbutazone, should trigger a conversation with your vet.
What to Do if You Suspect a Reaction
If you suspect your horse is reacting poorly to bute:
Stop giving further doses unless your vet advises otherwise.
Check and record vitals (temperature, heart rate, respiratory rate, mucous membranes): The horse’s vital signs
Note timeline and doses (how much bute, how often, for how many days).
Call your veterinarian with very clear, numbered information:
“Day 1: started bute at X grams once/twice daily for diagnosed condition.”
“Day 3: manure softer; Day 4: diarrhea and mild colic signs.”
Follow your vet’s advice, which may include:
Stopping NSAIDs
Supportive care (fluids, GI protectants, diet changes)
Bloodwork to check kidney function and protein levels
Ultrasound to check the right dorsal colon
Bute vs Other Options
Bute is not the only NSAID available for horses. Your vet will often choose between phenylbutazone (bute), flunixin meglumine (Banamine), and firocoxib (Equioxx) based on the type of pain, duration of treatment, and your horse’s risk factors.
To learn more, read NSAIDs for Horses: Bute vs. Fluxinin vs. Firocoxib
Phenylbutazone (Bute)
Bute is the classic choice for musculoskeletal pain. It is often used for lameness, arthritis flare-ups, tendon and ligament soreness, and general post-work stiffness.
Owners like it because it is effective and relatively inexpensive. It works well to take the edge off joint and limb pain.
The downside is that bute is tough on the stomach, colon, and kidneys, especially at higher doses, long courses, in dehydrated horses, or in horses with existing gut or kidney issues. It has a well-documented link with right dorsal colitis and other NSAID-related problems.
In most programs, bute is used for short bursts or carefully monitored longer plans, with your vet watching gut health, hydration, and sometimes bloodwork for early warning signs.
Flunixin Meglumine (Banamine)
Flunixin is also an NSAID, but it is especially strong for visceral pain, meaning pain from internal organs. In horses, that often means colic.
Vets like Banamine because it can provide fast, strong relief when the gut is painful, and it is also useful for certain eye problems and some systemic inflammatory conditions.
However, it has very similar gut and kidney risks to bute. It should not be given casually at home, and it should not be stacked with other NSAIDs.
In many barns, people think of it this way: bute for legs, Banamine for belly and eyes. That is oversimplified, but it reflects how they are often used in practice.
Firocoxib (Equioxx)
Firocoxib is a COX-2–selective NSAID. That means it aims more at inflammatory pathways and is gentler on the protective functions of COX-1.
It is approved for osteoarthritis pain and inflammation and is often given once daily as a longer-term arthritis option.
Because of its selectivity, Equioxx tends to cause fewer stomach and colon problems at labeled doses than older drugs like bute. It is not side-effect free, but it is often preferred when a horse needs daily, ongoing pain control and has some GI risk.
The trade-off is that it is usually more expensive and slower to “kick in” than some injectable options, so it is used more as a steady maintenance drug than a crisis drug.
Simple Comparison Table
Drug (common name) | Typical focus | Pros | Main cautions |
Bute (phenylbutazone) | Musculoskeletal pain, lameness | Strong, inexpensive, familiar | Higher GI/colon and kidney risk, especially with long/high dosing or dehydration |
Banamine (flunixin) | Colic, eye pain, systemic inflammation | Excellent for visceral pain and eye issues | Same NSAID risks; can mask colic severity; avoid stacking with other NSAIDs |
Equioxx (firocoxib) | Chronic arthritis, longer-term pain | COX-2 selective; often fewer GI issues at label doses | Still NSAID; cost; slower onset; needs correct loading and dosing plan |
Non-Drug Supports You Can Ask About
No matter which NSAID your vet selects, you can often reduce the required dose or duration by improving:
Rest and rehab planning (gradual return to work, clear time frames)
Footing and arena surface
Hoof balance and farriery (see your existing breakover and shoeing content)
Saddle fit and rider balance
Weight management and basic nutrition (link back to The basics of equine nutrition)
These “mechanical” and management changes are a big part of keeping your horse comfortable so you do not feel tempted to rely on bute alone.
Final Safety Notes and Next Steps
Bute for horses (phenylbutazone) is a powerful tool, not a barn “quick fix.” Used with a clear diagnosis, correct weight-based dosing, good hydration, and close monitoring, it can improve comfort and help your horse through short-term musculoskeletal pain. Used casually, or to push through red-flag problems like fever, colic, or neurological signs, it can hide serious disease and increase the risk of gut and kidney damage.
Your safest path is always:
Diagnosis first, then medication.
Lowest effective dose, for the shortest reasonable time, under veterinary supervision.
Honest tracking of vitals, manure, appetite, and attitude, using tools like:
For your own barn, consider keeping:
A medication log (dose, time, reason, response).
A printed vitals chart and fever chart on the stall door or in the tack room.
A one-page “Bute Safety Checklist” and “Show Rules reference” updated once a year with your vet and your current federation rules.
If you want structured learning and ready-to-print tools, point readers toward:
Memberships: full access to vitals, disease, and lameness content, plus checklists and planning tools.
Certifications and study materials for deeper understanding of equine health and lameness:
FAQs About Bute for Horses
Can I give bute for a low-grade fever?
It is safer not to give bute just to “knock down” a low-grade fever unless your veterinarian has examined the horse and recommended it. A fever is often an early sign of infection or systemic disease, and lowering it with phenylbutazone can hide how sick the horse really is. Check your horse’s temperature and other vitals, then compare them with the fever and vitals guides:
How long can I safely give bute?
Most label and guideline examples keep phenylbutazone use to short courses (for example, a few days up to about five days) at the lowest effective dose, with bloodwork and exams for any longer plan. Longer use increases the risk of stomach and colon ulcers, right dorsal colitis, and kidney damage, especially in dehydrated or high-risk horses. If your horse seems to need bute beyond a few days, that is a sign you and your vet should recheck the diagnosis and overall management, not just continue the same dose.
Can I combine bute with Banamine or Equioxx?
For most horses, the answer is no unless your veterinarian has deliberately planned and is closely supervising that combination. Stacking NSAIDs (for example, bute plus Banamine or bute plus Equioxx) amplifies the risk of gut and kidney injury. Competition rules also usually allow only one NSAID within the testing window, so combining drugs can create both a welfare and a rules problem.
Does bute hide lameness and risk further injury?
Yes. Bute for horses reduces pain and inflammation, which means a lame or sore horse may move more freely than it should. That can make a problem look mild when it is serious, and it can lead riders to keep working a horse with a soft-tissue injury, joint disease, or even a fracture. If your horse is significantly lame or non–weight-bearing, the answer is diagnostics first, not “more bute.”
What if my horse will not eat the powdered dose?
If your horse refuses medicated feed, do not keep adding more powder or hiding it in a huge meal, since you may lose track of the true dose. Instead, ask your vet about other options such as calibrated paste syringes, different flavours, or carefully measured tablets. Always feed a small, easily finished portion that you can watch your horse complete so you know the full dose was taken, and record what actually went in.
What are the show withdrawal times for bute?
Withdrawal times depend on the federation, dose, frequency, and your horse’s metabolism. USEF, Equestrian Canada, and FEI publish threshold levels and detection times, but they are not guarantees; you still need an extra safety margin set with your vet. The safest approach is to: use only one NSAID, stay within published dose limits, and create a written medication and withdrawal plan with your veterinarian based on the latest rules for your sport.
Signs of bute overdose or reaction—what should I watch for?
Warning signs include reduced appetite, new or worsening colic signs, soft manure or diarrhea, dark or tarry manure, dull attitude, and changes in urine amount or colour. You may also see increased heart rate, abnormal gums, or signs of dehydration despite water being available. If any of these appear after starting or increasing phenylbutazone, stop further doses, record your horse’s vitals, and call your veterinarian immediately, using your colic and vitals checklists:
Is bute safe for senior horses or pregnant mares?
Senior horses and pregnant mares can be more vulnerable to NSAID side effects, especially if they have early kidney disease, metabolic problems, or gut sensitivity. Bute may still be part of a plan for some of these horses, but only with careful veterinary supervision, conservative dosing, and close monitoring of weight, hydration, manure, and bloodwork. In many cases, your vet may prefer a different NSAID, a shorter course, or more emphasis on non-drug management such as nutrition, hoof balance, body condition control, and appropriate exercise, using resources like:
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