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. 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 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. Methotrexate, formerly known as amethopterin, is a chemotherapy agent and immune-system suppressant. It is used to treat cancer, autoimmune diseases, and ectopic pregnancies. Methotrexate is injected 1 day a week, on the same day of the week. For instance, if you give yourself the first injection on a Saturday morning, you will repeat the injection the next Saturday morning, and every Saturday morning after that. Use only preservative-free Methotrexate Injection for treatment of neonates or low birth weight infants and for intrathecal use. Methotrexate Injection: learn about side effects, dosage, special precautions, and more on MedlinePlus Learn about Rasuvo® (methotrexate) injection, an RA treatment option. Access co-pay cards, RA Coach, and patient support for an RA auto-injector. Methotrexate injection may be given by the intramuscular, intravenous or intra-arterial route. However, the preserved formulation contains Benzyl Alcohol and must not be used for intrathecal or.