NSAID Side Effects in Horses: Gut Risks Owners Should Know

By Dr Duncan Houston

Bute, Banamine, and Equioxx can be extremely useful, but they are not harmless painkillers.

NSAIDs are some of the most commonly used medications in equine practice. They help control pain, inflammation, fever, lameness, colic pain, and post-injury discomfort.

The problem is that they can also affect the gastrointestinal tract, especially the stomach, small intestine, and right dorsal colon. In some horses, side effects can appear even when treatment has only been used for a few days.

The goal is not to make owners scared of NSAIDs. The goal is to use them properly, monitor the right signs, and avoid the dangerous habit of treating these medications like casual stable cupboard extras.

Quick Answer

NSAIDs such as phenylbutazone, flunixin meglumine, and firocoxib can cause gastrointestinal side effects in horses, including gastric ulceration, reduced appetite, soft manure, diarrhoea, colic signs, and right dorsal colitis. Risk increases with high doses, prolonged use, dehydration, illness, kidney disease, liver disease, existing gut disease, and combining NSAIDs with other NSAIDs or corticosteroids. Even short courses should be monitored carefully, especially if the horse becomes dull, stops eating, develops loose manure, shows colic signs, or seems worse rather than better. (MSD Veterinary Manual)

What Are NSAIDs?

NSAIDs stands for non-steroidal anti-inflammatory drugs.

In horses, common NSAIDs include:

1. Phenylbutazone, commonly called bute

2. Flunixin meglumine, commonly known by the brand name Banamine

3. Firocoxib, commonly known by the brand name Equioxx

4. Meloxicam

5. Ketoprofen

These drugs reduce pain and inflammation by affecting cyclooxygenase pathways involved in prostaglandin production. Prostaglandins are not just involved in pain. They also help protect the gut lining, support blood flow to organs, and maintain normal tissue repair. This is why NSAIDs can relieve pain and still create risk elsewhere in the body. (MSD Veterinary Manual)

Why NSAIDs Are So Common In Horses

NSAIDs are used because they work.

They may be prescribed for:

1. Lameness

2. Arthritis

3. Soft tissue injuries

4. Laminitis pain

5. Colic pain

6. Fever

7. Post-surgical pain

8. Inflammatory conditions

9. Acute injury

10. Chronic musculoskeletal pain

Flunixin meglumine is specifically labelled for the relief of inflammation and pain associated with musculoskeletal disorders in horses, and for visceral pain associated with colic. The label also states that the cause of colic should be determined and treated with appropriate additional therapy. (DailyMed)

That last part matters. NSAIDs can reduce pain, but they do not diagnose the problem. A horse that feels better after Banamine may still have a serious underlying colic.

How NSAIDs Can Affect The Gut

NSAID-related injury can occur in more than one part of the gastrointestinal tract.

Important sites include:

1. Stomach

2. Small intestine

3. Large colon

4. Right dorsal colon

5. Mouth and oesophagus in more severe toxicosis cases

MSD Veterinary Manual notes that NSAID-induced injury can occur anywhere in the gastrointestinal tract, but the gastric mucosa and large colon, especially the right dorsal colon, appear particularly sensitive in horses. (MSD Veterinary Manual)

The gut lining needs protective mechanisms to stay healthy. NSAIDs can interfere with those mechanisms, especially when the horse is dehydrated, unwell, receiving high doses, treated for too long, or receiving more than one anti-inflammatory medication.

What Is Right Dorsal Colitis?

Right dorsal colitis is inflammation and ulceration of the right dorsal colon, a section of the large colon.

It is one of the most important serious gastrointestinal complications linked with NSAID use in horses. It can lead to protein loss through the gut, soft manure or diarrhoea, colic signs, weight loss, ventral oedema, and in severe cases, systemic illness or intestinal damage. (MSD Veterinary Manual)

This is not simply a mild upset stomach. Severe right dorsal colitis can become life-threatening.

The difficult part is that early signs may be subtle.

What The Research Shows About Short-Term NSAID Gut Effects

One preliminary study followed hospitalised horses treated with NSAIDs and compared them with untreated control horses. The study included 17 NSAID-treated horses and 5 controls. NSAID-treated horses developed thickened right dorsal colon walls in 4 of 9 scanned horses, subclinical or mild colitis in 9 of 11 horses, and right dorsal colitis in 4 of 10 horses. All control horses remained healthy. (ORBi)

The first changes were identified as early as treatment day 2, and the researchers concluded that presumptive colon pathology could appear early in the course of NSAID treatment, even though severity was generally low in that study. (ORBi)

This does not mean every horse given NSAIDs will develop severe colitis. It does mean owners and vets should monitor appetite, manure, comfort, hydration, and behaviour during treatment.

Why Mild NSAID Side Effects Are Easy To Miss

Early gastrointestinal side effects may not look dramatic.

A horse may simply show:

1. Slightly reduced appetite

2. Softer manure

3. Mild dullness

4. Mild colic signs

5. Less enthusiasm for work

6. Weight loss over time

7. Loose manure or manure staining

8. Mild ventral swelling

9. Reduced water intake

10. Behaviour change

These signs are easy to dismiss, especially if the horse is already being treated for pain.

That is the trap. Owners may assume the horse is quiet because of the original injury, when the medication may also be affecting the gut.

Which NSAIDs Carry The Most Gut Risk?

All NSAIDs can carry risk, but they are not identical.

MSD Veterinary Manual notes that toxicity is related to COX-2 selectivity, dose, and duration, and that nonselective COX inhibitors are hypothesised to have greater toxicity risk than COX-selective drugs. It also notes that phenylbutazone has greater ulcerogenicity than flunixin meglumine, while firocoxib appears safer. (MSD Veterinary Manual)

That does not mean firocoxib is risk-free.

The FDA label for Equioxx states that NSAIDs as a class may be associated with gastrointestinal, renal, and hepatic toxicity, that risk varies between individual horses, and that treatment should be stopped if signs such as inappetence, colic, abnormal faeces, or lethargy are observed. (animaldrugsatfda.fda.gov)

The practical message is:

Firocoxib may be a better choice for some horses, especially when longer-term anti-inflammatory therapy is needed, but it still requires veterinary direction and monitoring.

Risk Factors That Make NSAID Side Effects More Likely

A horse is at higher risk when NSAIDs are used in the wrong patient, at the wrong dose, for too long, or in combination with other medications.

Higher-risk situations include:

1. Dehydration

2. Reduced water intake

3. Colic

4. Diarrhoea

5. Fever

6. Kidney disease

7. Liver disease

8. Existing gastric ulcers

9. Existing colitis

10. Severe systemic illness

11. High dose NSAID use

12. Prolonged treatment

13. Combining two NSAIDs

14. Combining NSAIDs with corticosteroids

15. Poor appetite while still receiving medication

16. Older or medically fragile horses

The Banamine label states that NSAIDs may be associated with gastrointestinal and renal toxicity, and that patients at greatest risk for renal toxicity include those that are dehydrated, receiving diuretics, or have renal, cardiovascular, or hepatic dysfunction. (DailyMed)

Do Not Stack NSAIDs

One of the most dangerous owner habits is stacking pain relief.

Examples include:

1. Giving bute and Banamine together

2. Giving Banamine after bute without veterinary guidance

3. Giving Equioxx while another NSAID is still active

4. Adding corticosteroids while the horse is on an NSAID

5. Using leftover medication from a previous condition

The Banamine label warns that because many NSAIDs can induce gastrointestinal ulceration, concurrent use with other anti-inflammatory drugs such as other NSAIDs and corticosteroids should be avoided or closely monitored. The Equioxx label also states that concurrent use with other NSAIDs or corticosteroids should be avoided. (DailyMed)

More painkillers does not automatically mean better pain control.

Sometimes it just means more toxicity risk.

How Worried Should You Be?

The key rule is simple:

If your horse becomes dull, stops eating, develops diarrhoea, or shows colic signs while on NSAIDs, do not just keep giving the medication. Call your vet.

Signs Of NSAID-Related Gut Problems

Watch for:

1. Reduced appetite

2. Complete refusal to eat

3. Softer manure

4. Diarrhoea

5. Manure staining

6. Mild colic signs

7. Recurrent flank watching

8. Lying down more than usual

9. Weight loss

10. Dullness

11. Lethargy

12. Fever

13. Ventral oedema under the belly

14. Poor performance

15. Signs of pain when swallowing

16. Drooling or oral ulceration

17. Worsening rather than improving comfort

MSD Veterinary Manual lists clinical signs of NSAID toxicosis as including oral and lingual ulceration, hypersalivation, pain when swallowing, gastric ulceration, colic signs, anorexia, soft faeces, diarrhoea, ventral oedema, dehydration, fever, tachycardia, recurring colic, weight loss, and soft faeces in more chronic cases. (MSD Veterinary Manual)

What Else Can Look Like NSAID Gut Injury?

Not every horse with diarrhoea or colic while on NSAIDs has NSAID toxicosis.

Important differentials include:

1. Salmonella

2. Clostridial colitis

3. Antimicrobial-associated diarrhoea

4. Sand colic

5. Parasite-related disease

6. Grain overload

7. Right dorsal colitis from NSAID exposure

8. Gastric ulcers

9. Stress-related colitis

10. Impaction colic

11. Large colon displacement

12. Small intestinal obstruction

13. Liver disease

14. Kidney disease

15. Hindgut dysbiosis

16. Sudden feed change

17. Poor water intake

18. Infectious disease spreading through a stable

This is why the history matters. The vet needs to know which NSAID was given, how much, how often, for how long, whether any other medications were used, and whether the horse had pre-existing illness.

When Is This An Emergency?

Treat this as urgent if your horse is receiving or recently received NSAIDs and shows:

1. Diarrhoea

2. Repeated colic signs

3. Refusal to eat

4. Severe lethargy

5. Fever

6. Ventral swelling

7. Weight loss with soft manure

8. Pale, dark red, purple, or tacky gums

9. Dehydration

10. High heart rate

11. Collapse

12. Severe weakness

13. No manure

14. Severe abdominal pain

15. Signs worsening despite pain medication

NSAID-related intestinal ulceration can become severe enough to allow endotoxin and bacterial translocation, with clinical signs of systemic inflammation and septicaemia. (MSD Veterinary Manual)

A horse on pain relief that is becoming more painful, quieter, or less interested in food is not a horse to “watch for another few days.”

What Should You Do If Your Horse Is On NSAIDs?

Step 1: Follow the exact veterinary plan

Do not adjust the dose, frequency, or duration yourself.

NSAID safety is closely linked to dose and duration, and some horses can develop toxicity even at lower than recommended doses. (MSD Veterinary Manual)

Step 2: Monitor appetite every day

A horse on NSAIDs should keep eating.

Reduced appetite is one of the most important early warning signs. The Equioxx label specifically lists inappetence as a reason to terminate treatment and contact a veterinarian. (animaldrugsatfda.fda.gov)

Step 3: Watch manure carefully

Track:

1. Manure volume

2. Softness

3. Diarrhoea

4. Mucus

5. Dryness

6. Blood or black manure

7. Manure staining on the tail or hindlimbs

Abnormal faeces while on NSAIDs should not be ignored.

Step 4: Check hydration and water intake

Dehydration increases risk, especially for kidney injury.

Make sure the horse has constant access to clean water. If the horse is not drinking, is sweating, has diarrhoea, has colic, or is systemically unwell, speak to your vet before continuing medication.

Step 5: Do not combine anti-inflammatories

Do not stack bute, Banamine, Equioxx, meloxicam, corticosteroids, or other anti-inflammatory medications without direct veterinary instruction.

Step 6: Ask about bloodwork for longer courses

For longer NSAID courses, your vet may recommend blood testing to assess hydration, kidney values, liver values, protein, albumin, and inflammation.

The Equioxx label states that horses should undergo a thorough history and physical examination before NSAID therapy, and that appropriate laboratory tests should be conducted to establish baseline blood data and periodically during administration of any NSAID. (animaldrugsatfda.fda.gov)

What Not To Do

Common mistakes include:

1. Giving bute because the horse “looks sore” without speaking to a vet

2. Giving Banamine every time the horse seems uncomfortable

3. Using old medication from a previous injury

4. Combining two NSAIDs

5. Combining NSAIDs and steroids without guidance

6. Continuing medication when the horse stops eating

7. Ignoring soft manure or diarrhoea

8. Assuming Equioxx means no gut risk

9. Treating colic pain at home without diagnosis

10. Giving NSAIDs to a dehydrated or systemically unwell horse without veterinary direction

11. Extending the course because the horse improved

12. Masking signs that should trigger referral or further diagnostics

The biggest mistake is thinking of NSAIDs as harmless pain relief.

They are useful, but they are powerful.

Are COX-2 Selective NSAIDs Safer?

COX-2 selective NSAIDs, such as firocoxib, are designed to target inflammatory pathways while sparing more of the protective COX-1 activity.

That can reduce some risk compared with less selective NSAIDs. MSD Veterinary Manual notes that firocoxib appears safer than phenylbutazone and flunixin in relation to ulcerogenicity. (MSD Veterinary Manual)

But safer does not mean risk-free.

MSD also notes that although COX-2 selective NSAIDs theoretically should cause fewer gastrointestinal adverse effects, COX-2 selective NSAIDs have still been associated with gastritis, erosion, ulceration, and enteropathy in humans and animals. (MSD Veterinary Manual)

So the practical advice is:

Firocoxib may be appropriate for some horses, especially for longer-term inflammatory pain, but it still needs a veterinary plan and monitoring.

Does Omeprazole Prevent NSAID Colitis?

This is an important distinction.

Omeprazole reduces stomach acid and can help with certain gastric ulcer problems. It does not protect the right dorsal colon in the same way.

A horse can be on omeprazole and still be at risk of right dorsal colitis, diarrhoea, or hindgut injury from NSAID exposure.

Do not assume that adding ulcer medication makes NSAID use automatically safe.

How Vets Think About NSAID Safety

When I see a horse on NSAIDs, I am not only asking whether the pain is improving.

I am asking:

1. Why is the horse painful?

2. Is this the right NSAID for the problem?

3. Is the dose correct?

4. How long does the horse really need it?

5. Is the horse hydrated?

6. Is the horse eating normally?

7. Is manure normal?

8. Are there signs of colic?

9. Is there diarrhoea?

10. Does the horse have kidney, liver, or gastrointestinal disease?

11. Is the owner using any other medications?

12. Is the medication masking a worsening problem?

The real clinical skill is not just choosing a painkiller. It is choosing the safest pain control plan for that horse in that situation.

How To Reduce NSAID Gut Risk

You cannot remove all risk, but you can reduce it.

Use the lowest effective dose for the shortest appropriate time

This does not mean under-treating pain. It means avoiding unnecessary exposure once the horse no longer needs the medication.

Avoid stacking medications

Do not combine NSAIDs or combine NSAIDs with corticosteroids unless your vet specifically decides the benefit outweighs the risk.

Keep the horse hydrated

Hydration supports gut and kidney safety.

This is especially important during hot weather, illness, diarrhoea, sweating, travel, and colic.

Monitor appetite and manure

These are often the first signs something is wrong.

A horse that stops eating while on NSAIDs deserves attention.

Review longer courses carefully

Long-term pain management may require follow-up examinations, blood testing, diet review, lameness reassessment, and discussion of alternative pain control options.

Treat the cause, not just the pain

NSAIDs can reduce inflammation, but they do not fix every underlying issue.

A lame horse may need imaging, farriery, rest, joint therapy, controlled exercise, surgery, or a different management plan. A colic horse needs diagnosis, not just pain relief.

Prevention Plan For Owners

Can NSAID Gut Damage Be Treated?

Treatment depends on severity.

Your vet may recommend:

1. Stopping the NSAID

2. Switching pain control strategy

3. Fluids

4. Bloodwork monitoring

5. Ultrasound of the right dorsal colon

6. Protein and albumin monitoring

7. Diet modification

8. Gastroprotective medication if gastric disease is involved

9. Supportive care for diarrhoea or colitis

10. Referral for severe cases

MSD Veterinary Manual notes that tentative diagnosis may be based on NSAID history, clinical signs, and hypoproteinaemia, while ultrasound may detect colon thickening and gastroscopy can confirm gastric ulceration. (MSD Veterinary Manual)

The earlier the signs are recognised, the better the chance of stopping progression.

Helpful Related Reading

This article fits naturally with:

1. Right dorsal colitis from phenylbutazone use in horses

2. What to do first when your horse has colic

3. Impaction colic in horses

4. Equine gastric ulcers

5. Plant toxins and liver disease in horses

6. Parasite control in horses

7. Post-colic surgery recovery in horses

8. Feeding older horses safely

NSAID safety sits in the middle of pain, gut health, hydration, colic risk, and medication management.

FAQs

Can bute cause colitis in horses?

Yes. Phenylbutazone is linked with gastrointestinal ulceration and right dorsal colitis, especially with high doses, prolonged use, dehydration, illness, or individual sensitivity. Some horses may develop toxicity even at lower than expected doses. (MSD Veterinary Manual)

Is Banamine safer than bute?

Banamine and bute are used for different clinical situations, and both can cause adverse effects. MSD Veterinary Manual notes that phenylbutazone has greater ulcerogenicity than flunixin meglumine, but flunixin still carries gastrointestinal and renal risk. (MSD Veterinary Manual)

Is Equioxx safe for long-term use?

Equioxx may have a lower gastrointestinal risk profile than some nonselective NSAIDs, but it is not risk-free. The label warns that NSAIDs as a class may be associated with gastrointestinal, renal, and hepatic toxicity, and that signs such as inappetence, colic, abnormal faeces, or lethargy should prompt stopping treatment and contacting a veterinarian. (animaldrugsatfda.fda.gov)

Can I give bute and Banamine together?

Do not combine NSAIDs unless your veterinarian specifically instructs you to. The Banamine label warns that concurrent use with other anti-inflammatory drugs such as NSAIDs or corticosteroids should be avoided or closely monitored. (DailyMed)

What are early warning signs of NSAID gut problems?

Early warning signs include reduced appetite, dullness, softer manure, diarrhoea, mild colic signs, weight loss, ventral swelling, or a horse that seems worse while taking pain medication. These signs should be reported to your vet quickly.

Final Thoughts

NSAIDs are valuable medications. Horses need good pain control, and untreated pain is not kind, safe, or medically sensible.

But NSAIDs are not casual barn cupboard drugs. They can affect the stomach, colon, kidneys, liver, and overall recovery, especially when used for too long, at the wrong dose, in dehydrated horses, or in combination with other anti-inflammatory medications.

The safest approach is not fear. It is precision.

Use the right drug, for the right reason, at the right dose, for the right duration, in the right horse. Then watch appetite, manure, hydration, comfort, and attitude closely.

If the horse stops eating, develops loose manure, becomes dull, shows colic signs, or simply does not seem right while on NSAIDs, that is not a side note. That is the moment to call your vet.

If your horse is on bute, Banamine, Equioxx, or another anti-inflammatory and you are unsure whether appetite changes, soft manure, colic signs, or behaviour changes are concerning, ASK A VET™ can help you understand what to monitor and when veterinary care is needed.