Side Effects of Bute in Horses: What Every Owner Should Know

By Dr Duncan Houston

Quick Answer

Phenylbutazone (bute) is an effective pain relief medication in horses, but it can cause serious side effects, especially with high doses or long-term use. The most important risks include gastrointestinal damage, right dorsal colitis, kidney injury, and protein loss. Careful use and veterinary guidance are essential.

Bute is one of the most commonly used medications in horses.

It works well. That’s why it’s everywhere.

But it’s also one of the easiest drugs to misuse, and that’s where problems start.

What to do before giving bute

Before using bute:

1. Confirm the reason for use

2. Use the lowest effective dose

3. Avoid long-term use unless supervised

4. Ensure your horse is well hydrated

5. Do not combine with other NSAIDs or steroids

Most side effects come from pushing dose or duration too far.

What is bute

Bute, or phenylbutazone, is a non-steroidal anti-inflammatory drug (NSAID).

It works by reducing inflammation and pain through inhibition of COX enzymes.

It is commonly used for:

• lameness

• arthritis

• soft tissue injury

• post-exercise soreness

Why bute can cause problems

While bute reduces inflammation, it also reduces protective mechanisms in the body.

This includes:

• reduced blood flow to the gastrointestinal tract

• reduced protective mucus in the gut

• altered kidney blood flow

These effects are what lead to complications.

Right dorsal colitis

This is the most important complication to understand.

It affects the upper right colon and is strongly associated with NSAID use.

Signs include:

• persistent loose manure

• weight loss

• abdominal discomfort

• reduced appetite

In severe cases, it can become life-threatening.

Gastrointestinal ulcers

Bute can contribute to ulcer formation by reducing protective barriers in the gut.

This can affect:

• the stomach

• the small intestine

• the colon

Ulcers may not be obvious until they are advanced.

Protein loss and swelling

Damage to the intestinal lining can cause protein to leak into the gut.

This leads to:

• low blood protein (hypoalbuminemia)

• swelling under the abdomen or limbs

• poor healing

This is often linked with right dorsal colitis.

Kidney damage

Bute affects blood flow to the kidneys.

This becomes a problem when:

• the horse is dehydrated

• dosing is high

• use is prolonged

Kidney injury can develop quickly in at-risk horses.

Masking underlying problems

One of the more subtle risks:

Bute reduces pain, which can hide:

• fractures

• tendon injuries

• worsening lameness

This can lead to overuse and further damage.

Risk factors that increase complications

Certain situations increase risk significantly:

• dehydration

• high doses

• prolonged use

• combining with other NSAIDs or steroids

• illness or poor condition

These are the cases where problems often occur.

Signs to watch for

Early detection is critical.

Watch for:

• loose or abnormal manure

• reduced appetite

• lethargy

• weight loss

• swelling under the abdomen

• signs of discomfort

If something changes, don’t ignore it.

What to do if you suspect side effects

If you are concerned:

1. Stop bute immediately

2. Contact your veterinarian

3. Do not restart without advice

Your vet may recommend:

• fluid therapy

• blood tests

• gastrointestinal support medications

• dietary adjustments

Early action improves outcomes.

Safer alternatives

Depending on the situation, alternatives may include:

• other NSAIDs with different profiles

• controlled exercise programs

• supportive therapies

• joint medications

The goal is always to balance pain control with safety.

Responsible use

To use bute safely:

• follow veterinary guidance

• use the lowest effective dose

• limit duration where possible

• ensure hydration

• monitor closely

Short-term, controlled use is where bute works best.

FAQ

Can I give bute every day

Not long-term without veterinary supervision.

Is bute safe

Yes when used correctly, but it carries real risks if misused.

What is the most serious side effect

Right dorsal colitis is one of the most significant complications.

Can I combine bute with other medications

Not with other NSAIDs or steroids unless specifically directed by your vet.

Final thoughts

Bute is a powerful and useful medication.

The problem is not the drug itself. It’s how it is used.

Used correctly, it helps horses stay comfortable.

Used incorrectly, it can cause serious harm.

Still unsure what to do next?

Pain management in horses can be tricky.

Is bute the right choice?
Are you using it safely?
Are there better options?

If you’re unsure, getting guidance early helps you avoid complications.

The ASK A VET™ app gives you access to veterinary advice when you need it, helping you manage your horse’s health with confidence.