Arthritis medications with mouth sores as a side effect include: 

NSAIDs Methotrexate Tumor necrosis factor (TNF) blockers

Why Do NSAIDS Cause Mouth Sores?

Nonsteroidal anti-inflammatory drugs (NSAIDS) such as Motrin (ibuprofen) can increase your risk of getting mouth sores. Researchers from the Research Center at the University of Medicine and Dentistry of New Jersey found NSAIDs impair your body’s ability to repair soft oral tissue and heal from oral ulcers. 

Why Does Methotrexate Cause Mouth Sores?

Methotrexate naturally occurs in your body and increasing the levels with medication containing this substance is known to cause mouth ulcers.

A possible side effect of taking prescription methotrexate is mucositis, inflammation of the lining of your mouth. Patients taking high doses are even more susceptible.

Why Do TNF-Blockers Cause Mouth Sores?

It’s common to treat rheumatoid arthritis with immunosuppressant medications, including tumor necrosis factor inhibitors because they help suppress your body’s inflammation response. Because they suppress your immune system, latent conditions, such as the herpes simplex virus, which causes cold sores, or oral thrush can surface.

Oral thrush is a yeast infection that commonly presents as white patches on the tongue. Rubbing off the white patch reveals a red patch underneath and you might also have an unpleasant taste in your mouth or difficulty swallowing.

Treatments to Help Relieve Mouth Sores

In patients on methotrexate, taking daily folic acid, 1 mg or greater may reduce the incidence of mouth sores. If the problem persists, folinic acid (leucovorin) taken 8-12 hours after methotrexate may help without affecting the efficacy of methotrexate.

In patients who develop mouth sores on NSAIDs, it may help to switch to another NSAID or different therapy. Other treatments which may work to heal or prevent mouth sores include:

Supplemental folic acid (have your vitamin B12 checked as increased folic acid may mask occult B12 deficiency)YogurtAcidophilus

Local steroid therapy such as Kenalog or Orabase may help for a few ulcers, while a combination of dexamethasone/Benadryl/Maalox in a 1/1/1 solution (swish and spit out) may ease the symptoms of multiple ulcers and help to heal.

Many health conditions present with mouth sores as a symptom, including:

In Behçet’s (Beh-CHETS or Beh-SHETS) disease, both arthritis and mouth ulcers are symptoms In lupus, both joint pain and oral lesions are symptoms  In vasculitis (an unusual complication of rheumatoid arthritis), mouth ulcers are a symptom