Methotrexate is a chemotherapy agent that is used to treat certain types of cancer and also acts as an anti-rheumatic drug. Consult your doctor before taking the medicine as it has some serious side effects including death. Take the medication once a week by injection if there is any side effects by tablet. It is given between the skin and muscle instead of into the vein. Some possible side effects of Nausea, Abdominal pain, Dyspepsia, Mouth sores, rash bruising/bleeding, black stools, enlarged glands, and bone pain. Methotrexate injection use is to cure psoriasis or rheumatoid arthritis.