Which medications can cause mouth sores? A Guide to Identifying and Managing Drug-Induced Oral Lesions

October 11, 2025 •

4 min read

According to research, oral mucositis, a severe form of mouth sores, affects approximately 40% of patients undergoing cancer chemotherapy. If you are experiencing discomfort and suspect your prescribed treatment is the culprit, it is important to understand which medications can cause mouth sores, the mechanisms behind them, and what steps you can take for relief. This guide explores the various classes of drugs associated with oral lesions and provides practical management advice.

Quick Summary

This guide details the various medication classes, including chemotherapy agents, NSAIDs, and certain cardiovascular drugs, that can trigger mouth sores. It also explains the underlying mechanisms of these side effects and provides actionable steps for prevention and symptom management.

Key Points

Chemotherapy-Induced Mucositis: Cytotoxic drugs, like methotrexate and 5-FU, commonly cause painful oral ulcers by damaging the rapidly dividing cells lining the mouth.
NSAIDs and Other Drug Reactions: Medications such as ibuprofen and naproxen can sometimes trigger immune-mediated conditions like erythema multiforme or lichenoid drug reactions that affect the mouth.
Antibiotics and Oral Thrush: By disturbing the mouth's natural bacterial balance, antibiotics can lead to opportunistic yeast infections, presenting as white, painful oral patches.
Cardiovascular and Other Drug Links: Certain blood pressure drugs (ACE inhibitors, beta-blockers) and anti-angina medication (nicorandil) are known culprits for causing oral lesions and ulcerations.
Immune System Considerations: Immunosuppressant drugs used for autoimmune conditions can make a patient more vulnerable to oral infections and ulcers.
Medical Consultation is Key: If you suspect a medication is causing mouth sores, do not stop taking it without consulting your doctor, who can confirm the cause and recommend a safe course of action.

Understanding Drug-Induced Mouth Sores (Stomatitis)

Drug-induced mouth sores, medically known as stomatitis or oral mucositis, refer to inflammation and ulceration of the oral mucosa caused by a medication. The side effects can range from mild irritation to severe, painful ulcerations that interfere with eating, speaking, and swallowing. The mechanisms differ depending on the drug. Some medications have a direct toxic effect on the rapidly dividing cells of the mouth lining, while others trigger an immune-mediated or allergic reaction. Some drugs can alter the oral environment, leading to opportunistic infections, such as oral thrush.

Common Medication Classes That Cause Mouth Sores

Several types of medications across various therapeutic areas have been linked to the development of mouth sores. If you are taking any of the following drugs, and notice oral lesions, it is important to consult your healthcare provider.

Chemotherapy Agents and Radiation Therapy

This is one of the most well-known causes of severe oral mucositis. Cytotoxic chemotherapy drugs are designed to target and kill rapidly dividing cancer cells but also damage the healthy, fast-proliferating cells lining the mouth, leading to redness, inflammation, and ulceration. This condition typically begins within 5 to 10 days of starting treatment and can be extremely painful.

Examples: Methotrexate, 5-fluorouracil (5-FU), doxorubicin, and etoposide.
Targeted Therapies: Certain newer targeted cancer therapies, such as mTOR inhibitors (e.g., everolimus), have also been associated with aphthous-like ulcers.

Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)

While often used for pain and inflammation, some NSAIDs can paradoxically cause oral lesions. In rare cases, they can trigger a severe allergic-type reaction called erythema multiforme, which involves painful erosions and blisters in the mouth. NSAIDs have also been associated with lichenoid drug reactions.

Examples: Ibuprofen (Advil, Motrin), naproxen (Aleve), and aspirin.

Antibiotics and Antimicrobials

The use of antibiotics, especially broad-spectrum ones, can disrupt the natural balance of microorganisms in the mouth. This can lead to an overgrowth of Candida albicans, the fungus responsible for oral thrush, which appears as creamy white patches in the mouth.

Examples: Amoxicillin, ampicillin, tetracyclines, and cephalosporins.

Cardiovascular Medications

Some drugs used to treat heart conditions and high blood pressure can cause oral side effects.

ACE Inhibitors: Medications like captopril and enalapril have been linked to oral ulcerations and lichenoid reactions.
Beta-Blockers: Used for heart rhythm and blood pressure, these can cause lichenoid drug reactions.
Nicorandil: This anti-angina medication is known to cause painful and chronic oral ulcerations in some patients.

Immunosuppressants

These drugs, used for autoimmune diseases like rheumatoid arthritis or to prevent organ transplant rejection, can suppress the immune system, making the mouth more susceptible to ulcers and infections.

Examples: Methotrexate (even at low doses for RA), azathioprine, and cyclosporine.

Other Notable Medications

Anti-Seizure Medications: Phenytoin (Dilantin) can cause oral lesions, including gum overgrowth.
Antidepressants: Sertraline has been reported in rare cases to induce oral ulcerations.
Bisphosphonates: These osteoporosis drugs, including alendronate, can cause direct irritation and ulceration if not swallowed correctly.

Comparison of Medications and Their Oral Effects


Medication Class	Examples	Primary Mechanism	Common Oral Symptoms
Chemotherapy	Methotrexate, 5-FU	Cytotoxic effect on mucosal cells	Oral mucositis (redness, ulcers)
NSAIDs	Ibuprofen, Naproxen	Immune-mediated reaction (rare)	Oral ulcers, erythema multiforme
Antibiotics	Amoxicillin, Tetracyclines	Disruption of oral flora	Oral thrush (white patches), general sores
Immunosuppressants	Methotrexate, Cyclosporine	Immune suppression, infection risk	Oral ulcers, infections
Cardiovascular Drugs	Captopril, Nicorandil	Allergic or lichenoid reaction	Oral ulcers, lichenoid lesions
Antiepileptics	Phenytoin	Immune-mediated reaction	Oral ulcers, gingival overgrowth
Bisphosphonates	Alendronate	Direct chemical irritation (improper use)	Focal oral ulceration

What to Do if You Suspect Your Medication is the Cause

If you develop persistent or painful mouth sores after starting a new medication, take the following steps:

Consult Your Doctor: This is the most important step. Do not stop taking a prescribed medication on your own. A doctor can help confirm if the medication is the cause, adjust the dosage, or suggest an alternative.
Maintain Excellent Oral Hygiene: Brush gently with a soft-bristled toothbrush. Good hygiene can prevent secondary infections from developing in open sores.
Use Soothing Rinses: A salt water and baking soda rinse (1 teaspoon salt, 1 teaspoon baking soda in 4 cups of warm water) can soothe and cleanse the mouth. Your doctor may also prescribe stronger medicated rinses.
Adjust Your Diet: Opt for soft, moist foods and avoid those that are acidic, spicy, or crunchy, which can cause further irritation. Cold foods like ice cream or popsicles can also help numb the area.

Preventing Medication-Related Mouth Sores

Prevention is possible, especially in high-risk situations like chemotherapy:

Pre-Treatment Dental Exam: For patients about to undergo chemotherapy, a dental checkup to address pre-existing oral health issues can reduce the risk of severe mucositis.
Oral Cryotherapy: Sucking on ice chips during chemotherapy infusions of certain drugs can reduce the severity of mucositis.
Correct Administration: Ensure you are taking all medications exactly as prescribed. For instance, bisphosphonates must be swallowed with a full glass of water while remaining upright to prevent esophageal or oral irritation.

Conclusion

Mouth sores can be an uncomfortable and sometimes serious side effect of various medications, ranging from common NSAIDs and antibiotics to powerful chemotherapy agents. The root cause is not always the same, with mechanisms varying from direct cytotoxicity to immune reactions and opportunistic infections. The key to managing drug-induced oral lesions is to consult a healthcare professional, maintain diligent oral hygiene, and make dietary adjustments for comfort. By understanding the link between medication and oral health, you can take proactive steps to mitigate this adverse effect. For more information on oral complications from cancer treatment, please visit the National Cancer Institute website.

Frequently Asked Questions

Drug-induced mouth sores can appear as red, swollen patches (oral mucositis) or distinct, painful ulcers that look like canker sores, often with a white or yellow center surrounded by a red border.

The timing can vary. Chemotherapy-induced mucositis often develops within 5 to 14 days. Immune-mediated reactions or opportunistic infections may take longer to manifest.

Yes, some Nonsteroidal Anti-Inflammatory Drugs (NSAIDs), including ibuprofen, have been associated with oral lesions and can trigger reactions in sensitive individuals.

No, you should never stop a prescribed medication without first consulting your doctor. They can determine if the drug is the cause, assess the severity, and discuss alternatives or dosage adjustments.

Effective home care includes rinsing with salt water and baking soda, eating soft, bland foods, and avoiding spicy or acidic irritants. Sucking on ice chips can also provide temporary relief.

You should see a doctor if the mouth sores are severe, persistent, interfere with eating or drinking, or if you also have a fever. In the case of chemotherapy, it is important to notify your care team at the earliest sign of oral discomfort.

A doctor can help you with this diagnosis by reviewing your medication history and examining the sores. The timing of the sores' appearance relative to starting the medication is a key indicator, though other factors like infection or trauma are also possible causes.