You should contact your doctor if you develop symptoms of an infection, such as a fever or cough,or if you think you are having any side effects. If you develop symptoms of an infection while using this medication, you should stop it and contact your doctor. The most common side effects are gastrointestinal upseand elevations of liver function tests. About 1-3% of patients develop mouth sores (called stomatitis), rash, diarrhea, and abnormalities in blood counts. Some side effects do not cause symptoms, so it is important to have routine blood tests performed every 8-12 weeks. Methotrexate may cause cirrhosis (scarring) of the liver,but this side effect is rare and most likely to occur in patients who already have liver problems or are using alcohol or taking other drugs that are toxic to the liver. Lung problems (persistent cough or unexplained shortness of breath) can occur rarely when taking methotrexate. Slow hair loss is seen in some patients, but hair grows back when the person stops taking this medication. This can often be managed by taking folic acid. It is important to remember that most patients do not experience side effects, and that, for those who do, many of the minor side effects will improve with time.