KYT Dental Services
Methotrexate · Mouth ulcers

Methotrexate and mouth ulcers

Quick answer

Mouth ulcers are one of the most common side effects of methotrexate, even at the low doses used for rheumatoid arthritis and psoriasis. They are sometimes mild and self-limiting, sometimes a sign that the dose is too high or that folic acid supplementation is not working. Persistent or severe ulcers should be reported to your prescribing physician promptly. The dental management focuses on comfort, healing, and ruling out infection.

The mechanism
Why methotrexate causes mouth ulcers

Methotrexate works by inhibiting an enzyme that processes folic acid, which is essential for DNA synthesis. The cells most affected are those that divide rapidly, including cancer cells but also the cells lining the mouth, gut, and bone marrow. When the cells lining the mouth cannot replace themselves quickly enough, small areas of the lining break down, leaving painful ulcers.

The ulcers tend to appear in areas of natural friction (the inner cheeks, the tongue edges, the soft palate) and can range from a single small sore to widespread mucositis affecting most of the mouth. Patients on low-dose methotrexate for autoimmune disease usually have intermittent, manageable ulcers. Patients on high-dose methotrexate for cancer can have severe mucositis that affects eating and drinking.

Folic acid supplementation, prescribed routinely alongside methotrexate for autoimmune use, reduces but does not eliminate the risk. Patients who skip their folic acid dose or who do not take the prescribed amount tend to have more ulcers. The ulcers can also signal that methotrexate dosing is too high relative to what your body is clearing, which is why your prescribing physician needs to know about them.

Practical steps
What to do about methotrexate mouth ulcers
  • Take your folic acid (or folinic acid) exactly as prescribed. Missing doses is one of the most common reasons ulcers worsen.
  • Tell your prescribing physician about ulcers, especially if they are painful, recurrent, or interfering with eating. The methotrexate dose may need adjustment.
  • Use a soft-bristle toothbrush and brush gently around active ulcers. Rough brushing makes them worse.
  • Avoid alcohol-containing mouthwash, which burns and slows healing. Saltwater rinses (one teaspoon of salt in a cup of warm water) several times a day are gentler.
  • Avoid spicy, acidic, or sharp foods during active ulcers. Smooth, room-temperature foods are easier.
  • Get persistent ulcers evaluated. Ulcers that last more than two weeks or grow over time may not be from methotrexate at all.
Red flags
When to call your dentist
  • Mouth ulcers that do not heal within two weeks.
  • Ulcers that grow larger over time instead of getting smaller.
  • Widespread mouth sores covering large areas of the cheek, tongue, or palate.
  • Severe pain that prevents you from eating or drinking adequately.
  • Ulcers paired with fever, fatigue, or bruising elsewhere on the body, which could indicate methotrexate toxicity (this also warrants a call to your prescribing physician).
Common questions
What patients ask about Methotrexate and mouth ulcers.
How long do methotrexate mouth ulcers last?
Mild ulcers usually heal within seven to ten days. More severe mucositis can take two to three weeks. Ulcers that persist longer or worsen during methotrexate use should be reported to your prescribing physician.
Does folic acid really help with methotrexate ulcers?
Yes. Studies show folic acid (or folinic acid) supplementation significantly reduces the rate of mouth ulcers and other side effects in patients on low-dose methotrexate for autoimmune disease. The supplement is typically prescribed alongside methotrexate for this reason.
Are mouth ulcers a sign that methotrexate is working?
Not directly. Mouth ulcers are a side effect, not a marker of therapeutic effect. Some patients have mild ulcers throughout treatment with no relationship to how well the medication is controlling their underlying disease. If ulcers are interfering with quality of life, talk to your prescribing physician about the dose or about folic acid.
Can I get dental cleanings on methotrexate?
Yes, in most cases. Routine cleanings are safe on methotrexate. We may adjust the cleaning approach if you have active ulcers or if your bone marrow function is suppressed (which your physician monitors with blood tests). Mention any recent labs at your visit.
What about cosmetic dental work like teeth whitening on methotrexate?
Teeth whitening can be irritating to oral tissues even in patients not on methotrexate. On methotrexate, the threshold for irritation is lower, so we usually defer whitening until ulcers and mucositis are not active.
Talk to a dentist about your case
Bring your medication list to your visit.

General guidance is a starting point. Your specific dental plan depends on your medical history, your other medications, and what your mouth looks like in person. Schedule a consultation and we’ll walk through it.

Schedule a consultationCall (833) 598-3368

Reviewed by Dr. Isaac Sun, DDS.

This page is general information, not medical advice. Do not start, stop, or change any medication based on what you read here. Talk to your prescribing physician and your dentist about your specific situation.