Methotrexate is the most commonly used disease-modifying antirheumatic drug (DMARD). This is because it has been shown to work as well or better than any other single medicine. It is also relatively inexpensive and generally safe. Like other DMARDs, methotrexate has side effects; it can cause rash and stomach upset, can be toxic to the liver or bone marrow, and can cause birth defects. In rare cases, it can also cause shortness of breath. Regular blood work is necessary when taking methotrexate. Taking folic acid helps reduce some of the side effects. Methotrexate's biggest advantage could be that it has been shown to be safe to take for long periods of time and can even be used in children.