Data by DrugsWatch from a clinical trial suggests that 1 in 10 Truvada PrEP users risk experiencing one or a combination of the following adverse effects when using the medication: Back pain. Headache. Joint pain. Itching or skin rash. Skin discoloration and hyperpigmentation. Abdominal pain. Stomach pain. Diarrhea. Nausea. Vomiting. Upper respiratory tract infection. Swollen glands. Sinusitis. Fatigue. Dizziness. Trouble sleeping. Insomnia. Strange dreams. Immune Reconstitution Syndrome (a condition triggered by the drug whereby your immune system responds to past infections that may still be in your body). Depression. Weight loss. Bone density loss. Kidney problems. Liver problems (leading to Lactic acidosis). Prior to starting Truvada PrEP, you should notify your doctor if you have ever suffered from osteopenia, kidney disease or liver disease as there are a number of drug interactions that they will consider prior to recommending the treatment for you. Kidney problems, liver problems and bone density loss are potentially serious long term side effects of Truvada, therefore it is important to regularly monitor your kidney and liver function with a healthcare professional, in addition to measuring bone density, whilst using the preexposure prophylaxis medication. Truvada should be safe to take with erectile dysfunction medications such as viagra (sildenafil) and cialis (tadalafil) as there are no known drug interactions between them. The risk of experiencing each side effect will vary depending on the individual.