Overview: Methotrexate is used to treat certain types of arthritis, cancer, and severe psoriasis. Common side effects include nausea or vomiting, upset stomach, and mouth sores. Serious side. Methotrexate is a medication commonly used in the treatment of Rheumatoid Arthritis, Psoriatic Arthritis, and other autoimmune conditions. It works by suppressing abnormal high activity of your immune system to reduce inflammation, swelling, and damage to your joints. Methotrexate injection, a treatment for certain autoimmune diseases and cancers, can lead to various side effects. These range from common, mild reactions such as headache and nausea to. Methotrexate treats certain leukemias and lymphomas, mycosis fungoides, rheumatoid arthritis, polyarticular juvenile idiopathic arthritis in children, and severe psoriasis in adults. Learn about side effects, interactions, and indications. Methotrexate injection is used alone or together with other medicines to treat several types of cancer, such as breast, head and neck, lung, blood, bone, lymph node, and uterus cancers. Methotrexate injectable IV solution is used to treat certain cancers and psoriasis. It’s also used to treat rheumatoid arthritis (RA), including polyarticular juvenile idiopathic arthritis. Methotrexate injection is used in combination with other cancer treatments to treat gestational trophoblastic neoplasia and breast cancer in adults. Methotrexate injection is also used alone to treat squamous cell carcinoma of the head and neck in adults. People who receive injections of Methotrexate Injection into their spine (intrathecal methotrexate) can develop inflammation of the lining around the spinal nerves. Severe, occasionally fatal, skin reactions have been reported following single or multiple doses of methotrexate. Reactions have occurred within days of oral, intramuscular, intravenous, or. Methotrexate Injection: learn about side effects, dosage, special precautions, and more on MedlinePlus.