Side effects of lamivudine include fatigue, muscle aches, fever and chills, sore throat, nausea, stomach pain or cramps, and diarrhea. Serious side effects are rare, occurring in less than 1% of people taking lamivudine. They include inflammation of the pancreas, nerve damage, and buildup of lactic acid in the blood. About 25% of patients experience a temporary worsening, or flare, of hepatitis during the first few months of treatment. If flares are severe, it is important for researchers to determine whether they are caused by resistance to lamivudine or by the immune system acting against the hepatitis B virus or another liver condition. A flare of hepatitis can also occur when lamivudine is stopped, that is, a withdrawal. In such situations, testing for hepatitis B virus levels and other liver conditions is important. It may lead to other treatments or stopping lamivudine and taking another medication instead. While patients are participating in the study, they will have a careful evaluation of their hepatitis and general condition. They may have an improvement in their disease as a result of long-term lamivudine therapy.