Why do new medications cause mouth sores?

Have you ever noticed a sore in your mouth after starting a new medication? New medications can trigger mouth sores in a few ways: Some dry out your mouth, others cause an allergic-type reaction in the mouth's lining and some directly harm the fast-growing cells that make up your mouth's soft tissue. The sores usually fade once your body adjusts or the drug is stopped, but a dental provider should always take a look. 

What you will learn in this article: 

• Mouth sores after a new drug often come from dry mouth, an allergic-type reaction or direct tissue damage. 

• Dry mouth from medication can raise your risk of cavities and mouth infection. 

• Sudden, painful blistering or crusted lips after a new drug can signal a drug reaction that needs prompt attention. 

• These sores often clear up once the causing drug is addressed with your doctor's guidance, and a dental provider can help find the cause. 

If new mouth sores showed up after starting a medication, schedule an appointment with an Aspen Dental provider. Your care team can look at the sores, ask about your medications and help you figure out next steps. 

What causes mouth sores after starting a new medication? 

A medicine can affect your mouth in more than one way. It may lower saliva, trigger an immune reaction or harm fast-growing cells during treatments such as chemotherapy. 

Can medication cause dry mouth that leads to sores? 

Yes. Saliva keeps your mouth moist, clears away bits of food and helps control harmful germs. Many common medicines lower saliva flow. The National Institute of Dental and Craniofacial Research lists drugs used for depression, blood pressure and bladder problems among them. Signs of dry mouth can include cracked lips and mouth sores. Ongoing dryness also raises the chance of tooth decay and fungal infections.¹ 

Can a medication cause an allergic reaction in the mouth? 

Rarely, a medicine may trigger drug-induced erythema multiforme. This immune reaction can cause blisters and ulcers in the mouth and thick crusts on the lips. The exact process is not fully understood. 

A case report in Archive of Clinical Cases describes a man who developed burning mouth pain, bleeding ulcers and heavy lip crusting after taking diclofenac and cephalexin. The report lists nonsteroidal anti-inflammatory drugs (NSAIDs), some antibiotics and anti-seizure medicines as possible triggers. In this one case, clinicians stopped the suspected drugs, prescribed steroids and saw the sores fully heal within two weeks.² 

Can medication directly damage the mouth’s tissue? 

Yes, especially with some cancer treatments. The American Academy of Periodontology explains that chemotherapy, radiation to the head or neck and bone marrow transplants may affect healthy tissue in the mouth. Problems can include sore or swollen gums, ulcers, dry mouth, enamel wear, taste changes, jaw stiffness and slower healing. Lower saliva flow can also make infection more likely.³ 

How can you tell which type of mouth sore you have? 

The way your mouth feels and looks may offer clues: 

• A sticky or dry feeling, cracked lips or rough, burning tissue may go with dry mouth. 

• Blisters that break quickly, widespread ulcers or heavy crusts on the lips soon after starting a medicine may point to a rare drug reaction. 

• During cancer treatment, sores may appear with swollen gums, dry mouth, taste changes or slower healing. 

These signs can overlap, so do not try to diagnose the cause on your own. A dental provider can examine your mouth sores and review your medication list. Tell the doctor who prescribed the medicine when the sores started and whether your dose recently changed. 

Do mouth sores from medication go away on their own? 

Some do, but recovery depends on the cause. If the problem is dry mouth, your care plan might include a different dose or medicine or a product that replaces saliva.¹ Your doctor should decide whether any prescription changes are safe. Never stop a prescribed medication on your own. 

If sores appear during cancer treatment, tell both your cancer care team and your dental provider. If you are not sure whether to contact your oncologist or dental provider first, either one can help you plan the next step. 

When should you see a dental provider about mouth sores? 

See a dental provider if a sore is not improving, keeps returning or makes it hard to eat or drink. A dental provider can check whether it may have another cause, such as a canker sore, and whether it is past its usual healing time. 

Call the doctor who prescribed your medicine if the sores began after a new drug or dose change. MedlinePlus advises getting medical help when you appear to be reacting to a medicine. Call 911 if breathing becomes difficult or your tongue or face suddenly swells, since these can be signs of a serious allergic reaction.⁴ 

Mouth sores tied to a new medication should not be brushed off, and you do not have to manage them alone. Contact your local dental provider to have the sores checked and get guidance on protecting your mouth while it heals. 

Why do new medications cause mouth sores? FAQs 

Still have questions about mouth sores after starting a new medication? These answers cover a few common questions. 

How soon after starting a medication do mouth sores show up? 

Timing varies by medicine and by person. Write down when you started the medicine, when the sores appeared and whether your dose changed. This timeline can help your dental provider and prescribing doctor look for a connection. 

Can over-the-counter drugs cause mouth sores too? 

Yes. Medicines sold without a prescription can cause side effects or reactions too. Tell your dental provider and prescribing doctor about every medicine, vitamin and supplement you take. 

Should you stop taking a medication if it causes mouth sores? 

No. Stopping suddenly can be riskier than the sores themselves for some medications. Call the doctor who prescribed it and describe what you're seeing. If you have trouble breathing or sudden swelling, call 911. 

Can dry mouth from medication lead to bigger dental problems? 

Yes, especially if it goes untreated for months or years. A dental provider can check for early decay and suggest ways to keep your mouth moist before bigger problems develop. 

Sources 

¹ National Institute of Dental and Craniofacial Research, Health Info: “Dry Mouth.” https://www.nidcr.nih.gov/health-info/dry-mouth 

² National Institutes of Health, PubMed Central, Archive of Clinical Cases: “Drug induced erythema multiforme of the oral cavity.” https://pmc.ncbi.nlm.nih.gov/articles/PMC9769071/ 

³ American Academy of Periodontology, For Patients, Gum Disease Information: “Oral Health During Cancer Therapy.” https://www.perio.org/for-patients/gum-disease-information/oral-health-during-cancer-therapy/ 

⁴ National Library of Medicine, MedlinePlus, Medical Encyclopedia: “Drug allergies.” https://medlineplus.gov/ency/article/000819.htm