Methotrexate (MTX) is commonly used for the treatment of patients with rheumatoid arthritis (RA) and in several other forms of inflammatory arthritis and autoimmune disease. Methotrexate (MTX) remains the cornerstone therapy for patients with rheumatoid arthritis (RA), with well-established safety and efficacy profiles and support in international guidelines. Detailed Methotrexate dosage information for adults and children. Includes dosages for Rheumatoid Arthritis, Psoriasis, Breast Cancer and more; plus renal, liver and dialysis adjustments. More than 900,000 people in the U.S. take methotrexate, often as a first-line treatment for rheumatoid arthritis (RA). It’s also used at much higher doses to treat some forms of cancer. How Does It Work? Methotrexate interrupts the process that causes RA inflammation, which damages your joints and organs over time. Your doctor may call it a “DMARD,” which is a type of RA. Methotrexate is one of the commonly used medications in the treatment of rheumatoid arthritis. It may also be used to treat lupus, inflammatory myositis, vasculitis, psoriasis, psoriatic arthritis, scleroderma, and some forms of childhood arthritis. Although there is currently no cure for RA, there are medications that a doctor can prescribe to slow the progression of joint destruction and deterioration. One of the most popular and also most effective of these is a folate analog called methotrexate (MTX).