Bismuth Subsalicylate Side Effects

Overview

Bismuth subsalicylate is generally well-tolerated when used at recommended doses for short-term treatment. Most people experience few side effects, and those that do occur are typically mild and harmless. However, because it contains salicylate (related to aspirin), some precautions similar to those for aspirin apply.

Common Side Effects

The most frequently reported side effects of bismuth subsalicylate include:

Harmless Discoloration:

Temporary darkening or blackening of the tongue
Dark gray or black stools
These are not harmful and resolve after stopping the medication

Gastrointestinal Effects:

Constipation (less common than with loperamide)
Nausea (though the medication often treats nausea)
Mild stomach discomfort

Most of these effects are mild and temporary.

Black Tongue and Black Stools

The most noticeable side effect is temporary darkening:

What happens:

Bismuth reacts with trace amounts of sulfur in saliva and the digestive tract
Creates harmless black bismuth sulfide
Tongue may turn dark gray, brown, or black
Stools may turn very dark gray or black

Important notes:

This is completely harmless
It is not blood
It resolves completely within days of stopping bismuth subsalicylate
No treatment is needed
It does not indicate any problem with the medication

Distinguishing from blood in stool:

Bismuth-darkened stool: Even, consistent dark gray or black color throughout
Blood in stool: May appear bright red, maroon, or tarry black; often uneven distribution
If uncertain, consult a healthcare provider

Less Common Side Effects

Some people may experience:

Mild constipation
Temporary hearing changes or ringing in ears (with high doses or prolonged use)
Mild stomach upset or discomfort
Headache
Anxiety or confusion (rare, usually with excessive doses)

Serious Side Effects (Rare)

While uncommon, some serious side effects require immediate medical attention:

Allergic Reactions:

Rash, hives, or itching
Swelling of face, lips, tongue, or throat
Difficulty breathing
Severe dizziness

More likely in people with aspirin allergies.

Salicylate Toxicity:

Ringing in the ears (tinnitus)
Hearing loss
Severe nausea and vomiting
Rapid or deep breathing
Confusion or drowsiness
Fever

Bleeding:

Unusual bruising or bleeding
Blood in urine or stool (actual blood, not bismuth darkening)
Prolonged bleeding from cuts

If serious side effects occur, stop using bismuth subsalicylate and seek immediate medical attention.

Reye’s Syndrome Risk

Critical warning for children and teenagers:

Bismuth subsalicylate contains salicylate and should not be given to children or teenagers who have or are recovering from viral illnesses (chickenpox, flu, etc.) due to the risk of Reye’s syndrome.

Reye’s syndrome:

Rare but serious condition
Affects the liver and brain
Can be life-threatening
Associated with salicylate use during viral illnesses in children

This is why bismuth subsalicylate is generally not recommended for anyone under 18 with viral symptoms.

Because bismuth subsalicylate contains salicylate (aspirin-related compound), it can cause effects similar to aspirin:

Gastrointestinal irritation:

Stomach upset or discomfort (though often used to treat these symptoms)
Rare stomach ulceration with prolonged high-dose use

Bleeding risks:

Increased bleeding tendency
Particularly concerning when combined with blood thinners
May affect platelet function

Kidney effects:

Rare kidney problems with excessive use or in people with existing kidney disease

Tinnitus (ringing in ears):

Sign of excessive salicylate levels
Indicates need to stop medication

Risk Factors for Side Effects

Certain factors increase the likelihood or severity of side effects:

Aspirin Allergy

People allergic to aspirin are likely allergic to bismuth subsalicylate:

Can cause severe allergic reactions
Should avoid bismuth subsalicylate entirely
Choose alternative anti-diarrheal treatments

Blood Thinners

Taking anticoagulants increases bleeding risk:

Warfarin, apixaban, rivaroxaban, and other blood thinners
Salicylate enhances anticoagulant effects
May cause dangerous bleeding
Consult healthcare provider before use

Regular Aspirin or NSAID Use

Combining with aspirin or NSAIDs:

Increases total salicylate or NSAID intake
Increases gastrointestinal side effect risk
Raises bleeding risk
May lead to excessive salicylate levels

Kidney Disease

People with kidney problems:

May accumulate salicylates
Higher risk of toxicity
May experience worsening kidney function
Should consult healthcare provider before use

Gout

Salicylates can:

Affect uric acid levels
Interfere with gout medications
Potentially worsen gout in some cases

Excessive Dosing or Prolonged Use

Taking more than recommended or using for extended periods:

Increases all side effect risks
Can lead to salicylate toxicity
May cause hearing problems
Increases bleeding risk

Drug Interactions That Increase Side Effect Risk

Anticoagulants: Combining with blood thinners significantly increases bleeding risk:

Warfarin
Direct oral anticoagulants (apixaban, rivaroxaban, dabigatran)
Antiplatelet drugs (clopidogrel)

Diabetes Medications: Salicylates can affect blood sugar:

May enhance insulin and oral diabetes medication effects
Could lead to low blood sugar
Requires careful monitoring

Methotrexate: Bismuth subsalicylate can:

Increase methotrexate blood levels
Increase methotrexate toxicity
Serious interaction requiring avoidance or close monitoring

Other Salicylate Sources: Combining multiple salicylate-containing products:

Aspirin
Topical pain relief products containing salicylates
Other medications containing salicylates
Can lead to excessive total salicylate intake

Pregnancy and Breastfeeding Concerns

Pregnancy: Salicylate exposure during pregnancy, especially late pregnancy:

May affect fetal development
Could cause bleeding complications near delivery
May prolong labor or pregnancy
Generally should be avoided

Breastfeeding: Salicylates pass into breast milk:

May affect nursing infants
Could cause salicylate-related effects in infants
Generally recommended to avoid or use only with medical guidance

Comparison with Other Treatments

Compared to Loperamide:

Bismuth subsalicylate:

Generally causes less constipation
Has unique side effect of harmless darkening
Carries bleeding risks due to salicylate
Has more drug interactions
Includes allergy risk for aspirin-sensitive individuals

Compared to Antacids:

Bismuth subsalicylate:

Has additional anti-diarrheal effects
Contains salicylate (antacids generally do not)
Different mechanism and side effect profile

Minimizing Side Effects

To reduce the likelihood of side effects:

Use only at recommended doses
Do not exceed maximum daily limits
Use for short-term symptom relief only (1-2 days for diarrhea)
Avoid if you have aspirin allergy
Do not combine with blood thinners without medical supervision
Do not give to children or teenagers with viral illnesses
Stop use if ringing in ears develops
Maintain hydration

When to Stop Using Bismuth Subsalicylate

Discontinue bismuth subsalicylate and contact a healthcare provider if:

You develop ringing in the ears or hearing changes
Signs of allergic reaction appear
Unusual bruising or bleeding occurs
Symptoms worsen or do not improve after 2 days
Severe abdominal pain, fever, or bloody stools develop
You experience nausea, vomiting, or confusion
Any concerning symptoms arise

Distinguishing Normal from Concerning Effects

Normal, expected effects (not concerning):

Temporary dark discoloration of tongue
Dark gray or black stools
Mild taste changes

Potentially concerning (warrant medical evaluation):

Ringing in ears
Hearing changes
Unusual bleeding or bruising
Severe abdominal pain
Actual blood in stool (bright red or maroon)
Allergic reaction symptoms

Special Populations

Older Adults

Older adults may be more sensitive to salicylate effects:

Higher risk of bleeding complications
More likely to have conditions affected by salicylates
May take medications that interact with bismuth subsalicylate
Should use cautiously and at lowest effective doses

People with Multiple Health Conditions

Those with several medical conditions:

More likely to have contraindications
Higher risk of drug interactions
May require alternative treatments
Should consult healthcare provider before use

Sources

This information is based on FDA-approved prescribing information, clinical safety data, and peer-reviewed medical literature.