Can Co-amoxiclav Cause Mouth Ulcers? An In-Depth Analysis

October 8, 2025 •

5 min read

While diarrhea is the most common side effect of co-amoxiclav, affecting about 9% of users, oral issues can also occur [1.8.2]. The question many ask is, can co-amoxiclav cause mouth ulcers, and if so, why does it happen and what can be done about it?

Quick Summary

Yes, co-amoxiclav can cause mouth ulcers as a possible side effect [1.2.2, 1.2.4]. This article examines the mechanisms, distinguishes them from other causes, and provides detailed strategies for management and prevention.

Key Points

Direct Link: Co-amoxiclav (Augmentin) is known to cause mouth ulcers, sores, or white spots in the mouth as a potential side effect [1.2.2, 1.2.4].
Multiple Causes: The ulcers can result from disruption of oral flora, leading to conditions like oral thrush, or from direct inflammation (stomatitis) [1.8.1, 1.10.1].
Severe Reaction Warning: In rare cases, mouth ulcers can be an early symptom of Stevens-Johnson syndrome (SJS), a life-threatening skin reaction that requires immediate medical attention [1.2.1, 1.6.1].
Management: Mild ulcers can often be managed at home with saltwater rinses and by avoiding irritating foods, but a doctor should always be consulted [1.5.3, 1.5.4].
Medical Consultation is Key: Never stop taking a prescribed antibiotic without consulting a doctor. Seek immediate help if ulcers are severe or accompanied by a rash or fever [1.3.2, 1.6.1].
Distinguishing Features: Ulcers caused by co-amoxiclav often appear alongside other drug-related symptoms, unlike common canker sores which are often isolated [1.2.2, 1.9.4].
Other Oral Effects: Besides ulcers, co-amoxiclav can cause swelling of the tongue (glossitis), black 'hairy' tongue, and tooth discoloration, particularly in children [1.8.1, 1.3.3].

Understanding Co-amoxiclav (Augmentin)

Co-amoxiclav, widely known by brand names like Augmentin, is a combination antibiotic medication [1.8.5]. It consists of two active ingredients: amoxicillin and clavulanic acid. Amoxicillin is a penicillin-type antibiotic that works by stopping the growth of bacteria [1.8.5]. Clavulanic acid is a beta-lactamase inhibitor. Its job is to overcome resistance in bacteria that produce beta-lactamase, an enzyme that can destroy amoxicillin, thereby broadening the spectrum of bacteria the medication can effectively treat [1.8.5]. This powerful combination is prescribed for a variety of bacterial infections, including sinusitis, pneumonia, ear infections, bronchitis, urinary tract infections, and skin infections [1.8.5]. While highly effective, it comes with a range of potential side effects, from common gastrointestinal issues to less frequent but more severe reactions [1.8.1, 1.8.2].

Can Co-amoxiclav Cause Mouth Ulcers?

Yes, developing sores, ulcers, or white spots in the mouth is a recognized side effect of taking co-amoxiclav [1.2.2, 1.2.4]. Although less common than side effects like diarrhea or nausea, oral lesions are a possibility that requires attention [1.8.2]. The presentation can range from minor, irritating sores to more severe and painful ulcerations. In some instances, these oral lesions can be a sign of a more serious systemic reaction [1.2.1].

Potential Mechanisms Behind Mouth Ulcers

Several factors can contribute to the development of mouth ulcers while taking co-amoxiclav:

Disruption of Oral Flora: Antibiotics, especially broad-spectrum ones like co-amoxiclav, do not just target harmful bacteria; they can also disrupt the natural balance of beneficial microorganisms in the body, including the mouth [1.10.1, 1.10.5]. This disruption can allow for the overgrowth of other organisms, like the fungus Candida albicans, leading to oral thrush (mucocutaneous candidiasis), which can present with white patches and soreness [1.8.1]. This imbalance may also contribute to inflammation and ulcer formation [1.10.1].
Allergic & Hypersensitivity Reactions: For some individuals, mouth ulcers can be a symptom of an allergic reaction to the medication [1.7.2]. Swelling of the lips, tongue, or mouth can occur, and in more severe cases, it can be part of a widespread skin reaction [1.3.2].
Stevens-Johnson Syndrome (SJS): In very rare instances, mouth ulcers can be an early and prominent sign of a severe and life-threatening mucocutaneous disease called Stevens-Johnson syndrome (SJS) or Toxic Epidermal Necrolysis (TEN) [1.2.1, 1.3.1]. SJS is a severe hypersensitivity reaction that causes blistering and peeling of the skin and mucous membranes, including the inside of the mouth [1.6.4]. This condition is a medical emergency and has been reported in association with co-amoxiclav use in both adults and children [1.6.1, 1.6.4]. If you develop a rash, blisters, or peeling skin along with mouth sores and fever, seek medical help immediately [1.7.2].
Stomatitis and Glossitis: Inflammation of the mouth (stomatitis) and tongue (glossitis) are listed as potential gastrointestinal side effects of co-amoxiclav [1.8.1, 1.8.4]. This inflammation can manifest as redness, swelling, soreness, and the formation of ulcers [1.3.3].

Comparison Table: Co-amoxiclav Ulcers vs. Common Canker Sores


Feature	Mouth Ulcers from Co-amoxiclav	Common Aphthous Ulcers (Canker Sores)
Timing	Typically develop during or shortly after a course of antibiotics [1.2.1].	Can occur at any time, often linked to stress, minor injury, or hormonal changes [1.9.4].
Primary Cause	Directly or indirectly related to the medication (e.g., flora disruption, allergic reaction) [1.4.4, 1.10.1].	Often idiopathic (unknown cause), but linked to triggers like stress, food sensitivities, or nutritional deficiencies (B12, iron, folate) [1.9.2, 1.9.3].
Accompanying Symptoms	May be accompanied by other drug side effects like diarrhea, rash, or signs of a systemic reaction like fever [1.2.2, 1.3.4].	Usually an isolated issue, though may be associated with underlying conditions like Crohn's disease in some cases [1.9.3].
Appearance	Can vary; may appear as white spots (thrush), red inflamed sores (stomatitis), or severe blistering lesions (SJS) [1.2.2, 1.8.1].	Typically round or oval with a white or yellow center and a red border [1.9.4].
Resolution	Often resolves after the medication is discontinued, though management may be needed [1.2.3]. Severe cases require immediate medical intervention [1.6.1].	Usually heal on their own within 1-2 weeks [1.9.3].

Managing and Treating Co-amoxiclav Induced Mouth Ulcers

If you develop mouth ulcers while taking co-amoxiclav, it is crucial to consult your doctor before stopping the medication. For mild cases, your healthcare provider may recommend supportive care to manage symptoms while you complete your antibiotic course.

At-Home Care and Management

Maintain Good Oral Hygiene: Brush gently with a soft-bristled toothbrush to avoid further irritation [1.5.3, 1.9.5].
Use a Saltwater Rinse: Rinsing your mouth several times a day with a warm saltwater solution can help keep the area clean and soothe discomfort [1.5.3]. A baking soda rinse can also be effective [1.9.5].
Avoid Irritating Foods: Stay away from foods and drinks that are spicy, acidic (like citrus fruits and tomatoes), salty, or have a rough texture (like toast or crisps) [1.5.4, 1.9.2].
Topical Anesthetics: Over-the-counter oral gels or rinses containing benzocaine (like Orajel) can provide temporary pain relief [1.5.3].

When to See a Doctor

You should contact your doctor right away if you experience any of the following:

The mouth ulcers are severe, numerous, or prevent you from eating or drinking [1.9.2].
You develop a skin rash, blistering, peeling skin, fever, or swelling of the face and tongue, as these could be signs of a severe allergic reaction or SJS [1.2.1, 1.3.2].
The ulcers do not improve after you have finished your course of antibiotics.

A doctor can determine the underlying cause and may prescribe treatments such as antiseptic mouthwashes, topical corticosteroids, or other medications to manage the condition [1.5.4]. In the case of a severe reaction, immediate discontinuation of the drug and emergency care are necessary [1.6.1].

Conclusion

In conclusion, co-amoxiclav can indeed cause mouth ulcers. This side effect can stem from a disruption of the mouth's natural microbial balance, a direct inflammatory reaction (stomatitis), or, in rare cases, a serious systemic hypersensitivity reaction like Stevens-Johnson syndrome [1.2.4, 1.6.1, 1.8.4]. While often mild and manageable with home care, it's vital for patients to monitor their symptoms closely. Differentiating between a simple ulcer and a sign of a more severe reaction is key. Always consult a healthcare professional for a proper diagnosis and treatment plan, especially if mouth sores are accompanied by other concerning symptoms like a rash or fever. Never discontinue your prescribed antibiotic course without medical advice.

For more information on the diagnosis and treatment of canker sores (aphthous ulcers), you can visit Ada's comprehensive guide.

Frequently Asked Questions

Side effects like mouth ulcers can appear at any time during the course of treatment, sometimes within a few days of starting the medication [1.6.1]. Severe reactions like SJS can develop weeks to months after starting [1.3.2].

Not necessarily. While they can appear similar, ulcers from co-amoxiclav are a drug-induced side effect and may be accompanied by other symptoms like a rash or thrush, whereas common canker sores (aphthous ulcers) are often triggered by stress or minor injury [1.2.2, 1.9.4].

You should contact your doctor for advice. For mild sores, they may suggest home remedies like saltwater rinses. Do not stop taking the antibiotic without medical guidance [1.2.3, 1.5.3].

Yes. If mouth ulcers are accompanied by a skin rash, blistering, fever, or swelling of the face, lips, or tongue, it could signify a severe reaction like Stevens-Johnson syndrome (SJS) and you should seek emergency medical help immediately [1.2.1, 1.3.2].

In most cases, drug-induced mouth ulcers will begin to heal and resolve after the medication is stopped [1.2.3]. If they persist or worsen, you should follow up with your healthcare provider.

While probiotics are studied for preventing antibiotic-associated diarrhea, their effect on oral ulcers is less clear. Antibiotics can disrupt the oral flora, which might contribute to ulcers, but specific evidence for probiotic prevention is limited [1.10.1].

Besides ulcers, co-amoxiclav can cause inflammation of the tongue (glossitis), black 'hairy' tongue, oral thrush (candidiasis), and, rarely, tooth discoloration, especially in children [1.8.1, 1.8.4].