Emtricitabine/tenofovir disoproxil fumarate (Truvada) can cause a range of side effects, which can vary from person to person. Common mild side effects include tiredness, headaches, diarrhea, nausea, headache, and appetite loss. These often improve within a few weeks. Serious side effects can include lactic acidosis, liver problems, kidney problems, bone changes, immune system changes, and allergic reactions. Lactic acidosis can lead to too much lactic acid in the blood. Liver problems can cause liver enlargement or fatty liver. Kidney problems can lead to kidney failure or Fanconi syndrome. Bone changes can lower calcium or mineral levels in bones, leading to bone pain and weaker bones. Immune system changes can cause immune reconstitution inflammatory syndrome (IRIS), which helps your immune system fight off hidden infections. Allergic reactions may include symptoms such as rash, itching, or difficulty breathing. Always consult your doctor about any side effects and follow their instructions.