When you take methotrexate, your doctor will order blood tests every six weeks to check your liver function. The drug works by triggering your body’s cells to release a substance called adenosine, which blocks inflammation. However, it can also lead to scar tissue in the liver, which may, rarely, develop into liver disease. Your doctor will likely prescribe folic acid, which can prevent scar tissue and other side effects. Still, keeping an eye on your liver function is essential.