Pepto-Bismol® (Bismuth Subsalicylate) for Horses: Uses, Side Effects & Status in Competition

Bismuth subsalicylate is a gastrointestinal medication that may be prescribed for horses as a supportive therapy for diarrhea and intestinal irritation. Although widely available over-the-counter for human use, its use in horses is off-label and should only be administered under veterinary guidance.

In horses, diarrhea and gastrointestinal upset can arise from a range of causes, including dietary changes, stress, infection, or inflammation. While bismuth subsalicylate may help reduce fluid loss and protect the intestinal lining, it does not address the underlying cause of disease and is typically used as part of a broader treatment plan.

Because the drug contains both a locally acting bismuth component and a systemically absorbed salicylate, its effects and safety profile differ from many other gastrointestinal therapies.

This dual action can influence both its benefits and potential risks, particularly when used alongside other medications or in horses with certain health conditions.

Bismuth Subsalicylate for Horses

Bismuth subsalicylate is an orally administered gastrointestinal medication labeled for human use. It is commonly used as an antidiarrheal medication and is available over-the-counter in many regions. ^[1]

Its therapeutic effects are derived from two components. The bismuth portion acts locally within the gastrointestinal tract, while the salicylate component is absorbed systemically and contributes anti-inflammatory effects.

This composition allows the drug to exert multiple actions within the digestive system, including mucosal protection, reduction of intestinal secretion, and modulation of inflammation. ^[1][2]

The separation of local and systemic activity is a defining feature of this drug. The bismuth component primarily contributes to local gastrointestinal effects, while the salicylate component is responsible for systemic pharmacologic activity.

Available Forms

The use of bismuth subsalicylate in horses is extra-label (off-label), meaning it is not specifically approved for use in this species. ^[1] Veterinarians are permitted to prescribe bismuth subsalicylate for equine use at their discretion, and they determine dosages based on the individual horse’s condition.

Bismuth subsalicylate is available over-the-counter in generic preparations and under the brand name Pepto-Bismol^® and others, including:

• Kaopectate^®
• Maalox Total Relief^®
• Pink Bismuth^®

Over-the-counter bismuth subsalicylate products are labeled for human use and are available in oral formulations, including:

• Suspensions (liquids)
• Chewable tablets
• Swallowed tablets
• Capsules

Bismuth subsalicylate is also available in veterinary formulations for non-equine species. Veterinary brand names include:

• Bismusol^®
• Bismusal^®
• BismuPaste^® ETM
• Gastro-Cote^®

Although bismuth subsalicylate is available over-the-counter, it should only be used in horses under veterinary guidance. Its use in equines is extra-label and requires appropriate oversight to ensure safety and efficacy.

Drug Class: Antidiarrheal & Gastrointestinal Protectants

Bismuth subsalicylate is classified as an antidiarrheal and gastrointestinal protectant. ^[1]

These classes of drugs include agents that reduce intestinal fluid secretion, protect the mucosal lining of the gastrointestinal tract, and bind toxins or irritants within the intestine. These medications are typically used as supportive therapies rather than definitive treatments, particularly when the underlying cause of diarrhea is unknown or multifactorial. ^[1][3]

Examples of related or functionally similar therapies used in horses include: ^[3]

• Dioctahedral smectite (DTO smectite)
• Activated charcoal
• Kaolin/pectin formulations

These agents differ in their mechanisms of action and are not pharmaceutical medications, but share the goal of stabilizing the intestinal environment to reduce gastrointestinal clinical signs.

In many cases, these products are selected based on the suspected underlying mechanism of disease, such as toxin-mediated diarrhea or mucosal inflammation. Their use is often guided by clinical judgment rather than strong comparative evidence. ^[3]

Mechanism of Action

Bismuth subsalicylate works both locally in the gastrointestinal tract and systemically after absorption.

Within the gastrointestinal tract, the compound is broken down into bismuth salts and salicylic acid. ^[2] The bismuth component largely remains within the intestinal wall, where it binds to mucosal surfaces and forms a protective coating. ^[2][3] This coating may help reduce irritation and limit contact between toxins and the intestinal lumen.

The salicylate component is absorbed and provides anti-inflammatory effects. ^[2][3] It is thought to work by reducing prostaglandin production, which can decrease both inflammation and fluid secretion in the intestine. ^[3] This may help limit the amount of fluid entering the intestinal tract.

Salicylate may also help reduce inflammation in the intestinal lining and support the integrity of the mucosal barrier, which can help limit irritation during gastrointestinal disease. ^[3]

Several mechanisms, including reduced intestinal secretion, toxin binding, and antimicrobial activity, have been described in other species, but these effects have not been directly demonstrated in horses. ^[1][3][4]

In addition, studies in horses confirm the drug does not function as an antacid in equine patients. ^[5] Any observed symptom relief in horses is more likely related to mucosal protection or modulation of inflammation. ^[6]

Uses in Horses

Because all use of bismuth subsalicylate in horses is off-label, veterinarians rely on published research, clinical trials, and professional experience to guide treatment. ^[1]

“Off-label” (or extra-label) use refers to administration of a drug in a manner not described on the FDA-approved package insert. This includes using the drug in a non-approved species. Veterinary regulations permit licensed veterinarians to prescribe drugs for extra-label use at their professional discretion.

Bismuth subsalicylate may be prescribed for horses as a supportive therapy for gastrointestinal disorders, particularly those involving diarrhea.

Common indications in humans and other species include: ^[3][6]

• Mild or nonspecific diarrhea
• Gastrointestinal irritation
• Supportive management of GI disease

In clinical practice, bismuth subsalicylate is typically incorporated into a broader treatment plan that may include fluid therapy, dietary management, and other medications.

Its primary role is to provide symptomatic relief rather than to address the underlying cause of disease. As a result, it is most often used as an adjunctive therapy rather than a primary treatment. ^[3][6]

Because equine diarrhea commonly involves large intestinal inflammation, microbial imbalance, and toxin exposure, therapies and management changes that directly target these processes may be more effective. Bismuth subsalicylate may still be considered in mild cases or when additional mucosal protection and anti-inflammatory support are desired. ^[3]

Administration Routes

Bismuth subsalicylate is administered orally in horses. Because its use is off-label, standardized dosing recommendations are not universally established.

The drug may be given with or without food and should be spaced from other medications when possible to reduce the risk of interference with drug absorption. ^[1] In some cases, dividing doses throughout the day may help maintain more consistent therapeutic effects.

Storage

Always store medications according to the directions on the label.

Most formulations of bismuth subsalicylate have the following storage conditions:

• Room temperature: 20 to 25°C (68 to 77°F)
• Protect from excessive heat or freezing
• Keep out of reach of children and animals

Shake liquid formulations thoroughly before use. ^[1]

Safety Warnings & Precautions

Although considered relatively safe, bismuth subsalicylate carries several important precautions.

The salicylate component introduces potential systemic effects, particularly with repeated dosing or high doses. ^[2] Use caution in horses receiving nonsteroidal anti-inflammatory drugs (NSAIDs), animals with kidney disease, or patients at risk of bleeding disorders. ^[1][3]

Systemic salicylate exposure may contribute to gastrointestinal irritation or changes in normal inflammatory responses. Given this, careful dosing and monitoring are important when using this medication in equine patients.

The drug may also interfere with absorption of other orally administered medications, making timing of administration important. ^[1] This is particularly relevant in horses receiving multiple medications as part of a treatment plan.

In addition, fecal discoloration caused by the drug should not be confused with melena (black stool), which may indicate gastrointestinal bleeding.

Monitoring

Horses receiving bismuth subsalicylate should be monitored for: ^[1][3]

• Persistent or worsening diarrhea
• Signs of dehydration
• Changes in appetite
• Changes in behavior
• Changes in manure quality or consistency beyond expected discoloration

Monitoring hydration status is especially important in horses with ongoing diarrhea, as fluid loss can occur rapidly. Clinical parameters such as mucous membrane (gum) moisture, skin tenting and overall demeanor can provide useful information about hydration and systemic status. ^[3]

Ongoing assessment of fecal consistency and frequency can help determine whether the treatment is providing symptomatic relief. If clinical signs do not improve within a short period, further diagnostic evaluation is warranted. ^[1][3]

Contraindications

Contraindications refer to circumstances where a drug should be avoided or used with caution.

Contraindications for bismuth subsalicylate in horses include: ^[1]

• Known hypersensitivity to salicylates or related compounds (including aspirin and some NSAIDs)
• Concurrent gastrointestinal ulceration or bleeding disorders
• Use in animals requiring diagnostic abdominal imaging, as the drug may interfere with radiographic interpretation

Caution is also advised in horses with impaired kidney function, as salicylate is eliminated through the kidneys. ^[3] Additionally, use in very young animals may warrant extra care due to differences in drug metabolism and absorption. Avoid use of bismuth subsalicylate in pregnant mares, as it is a potential teratogen. ^[1]

Side Effects

Bismuth subsalicylate is generally well-tolerated in horses when used as directed by a licensed veterinarian.

Common side effects include mild constipation and darkening of feces due to formation of bismuth sulfide. ^[1][2] These changes are typically harmless and do not require intervention.

Less common effects may include gastrointestinal discomfort and reduced appetite. ^[1] In most cases, these signs are mild and resolve after discontinuation of the drug.

Because the salicylate component is systemically absorbed, there is potential for more significant effects if dosing is excessive or prolonged.

Acute Toxicity (Overdose)

Overdose of bismuth subsalicylate can result in toxicity, primarily related to the salicylate component.

Signs of overdose in horses may include: ^[1]

• Gastrointestinal irritation
• Changes in body weight or condition
• Lethargy
• Uncoordinated movements and weakness
• Systemic illness

In rare cases, excessive or prolonged exposure to bismuth compounds has been associated with neurologic toxicity, although this is uncommon with standard use. ^[2]

Seek prompt veterinary attention if overdose is suspected or if severe clinical signs develop. Early intervention may help reduce the risk of complications and support recovery.

Drug Interactions

Bismuth subsalicylate may interact with other medications through several mechanisms.

Potential interactions include: ^[1][2]

• Increased risk of side effects when combined with other salicylates (e.g., aspirin) or nonsteroidal anti-inflammatory drugs (NSAIDs)
• Reduced absorption of concurrently administered oral medications when given within a short time frame
• Interference with absorption of certain drugs, including tetracycline antibiotics, particularly with some tablet formulations

Additionally, concurrent use with other gastrointestinal adsorbents, such as activated charcoal or dioctahedral smectite, may alter overall effectiveness by competing for binding within the intestinal lumen. ^[3]

Use alongside certain cathartics or surfactants, such as dioctyl sodium sulfosuccinate (DSS), may increase the risk of adverse gastrointestinal effects. ^[3]

Because equine patients with gastrointestinal disease are often treated with multiple therapies, including anti-inflammatory drugs, adsorbents, and cathartics, it is important to have veterinary oversight when using this medication.

The treating veterinarian will review use of bismuth subsalicylate in the broader context of the treatment plan, ensuring safe use and monitoring as required. ^[1][3]

Regulatory Status & Legal Considerations

Bismuth subsalicylate is an over-the-counter (OTC) medication widely available in human pharmacies, but its use in horses is off-label in veterinary medicine.

This means it has not been specifically approved for equine use by regulatory agencies, and there are no standardized labeled dosing instructions for this species.

As per veterinary regulations and federal drug law, off-label applications must be prescribed by a licensed veterinarian within a valid veterinary-client-patient relationship (VCPR).

The prescribing veterinarian is responsible for determining whether use of the drug is appropriate, as well as establishing dosing, administration, and monitoring protocols based on the individual horse’s condition.

Because of its extra-label status, careful oversight is required to ensure safe and effective use, particularly in performance horses or animals receiving concurrent medications.

Status in Competition

Bismuth subsalicylate is not listed in the Fédération Équestre Internationale (FEI) clean sport database of banned substances, which means it may be permitted in and out of FEI-sanctioned competition. ^[7]

Always check the rules for your sport and work with your veterinarian to determine appropriate timing before starting a competition horse on a new medication.

Frequently Asked Questions

Here are some frequently asked questions about bismuth subsalicylate for horses:

Summary

Bismuth subsalicylate is an oral gastrointestinal medication used as a supportive therapy for diarrhea in horses, though its use is off-label and supported by limited equine-specific evidence. It may provide mucosal protection and mild anti-inflammatory effects, but is typically used alongside other treatments rather than as a primary therapy.

• Used off-label as a supportive treatment for horse diarrhea, particularly mild or nonspecific cases
• Works by coating the intestinal lining and providing anti-inflammatory effects via salicylate absorption
• Additional mechanisms described in other species, such as toxin binding, are not well-demonstrated in horses
• It does not act as an antacid in horses, as it does not significantly affect stomach acidity
• Generally well-tolerated, but may cause darkened feces, mild constipation, or reduced appetite
• Should be used under veterinary guidance, especially when combined with other medications or in more severe cases