Emtricitabine (commonly called FTC, systematic name 2',3'-dideoxy-5-fluoro-3'-thiacytidine), with trade name Emtriva (formerly Coviracil), is a nucleoside reverse-transcriptase inhibitor (NRTI) for the prevention and treatment of HIV infection in adults and children. Emtricitabine is also marketed in a fixed-dose combination with tenofovir disoproxil (Viread) under the brand name Truvada, and with tenofovir alafenamide (Vemlidy) under the brand name Descovy. A fixed-dose triple combination of emtricitabine, tenofovir and efavirenz (Sustiva, marketed by Bristol-Myers Squibb) was approved by the U.S. Food and Drug Administration (FDA) on July 12, 2006, under the brand name Atripla. Emtricitabine makes up one fourth of the Quad pill (brand names: Stribild and Genvoya). In fixed-dose combinations with tenofovir or with efavirenz and tenofovir it is on the World Health Organization's List of Essential Medicines. In 2019, it was the 494th most commonly prescribed medication in the United States, with more than 3thousand prescriptions. Medical uses HIV infection Emtricitabine is indicated in combination with other antiretroviral agents for the prevention and treatment of HIV-1 infection. HBV infection Emtricitabine exhibits clinical activity against the hepatitis B virus (HBV), but is not approved by the U.S. Food and Drug Administration (FDA) for the treatment of HBV infection. Among individuals with chronic HBV infection, emtricitabine treatment results in significant histologic, virologic, and biochemical improvement. The safety profile of emtricitabine during treatment is similar to that of a placebo. Emtricitabine, like all other FDA approved drugs, cures neither HIV nor HBV infection. In a study involving individuals with HBV infection, symptoms of infection returned in 23% of emtricitabine-treated individuals who were taken off therapy. In studies involving individuals with chronic HIV infection, viral replication also resumes when study subjects are taken off therapy. As with drugs used to treat HIV infection, drugs used to treat HBV infection may have to be used in combination to prevent the evolution of drug resistant strains. The effectiveness of emtricitabine in combination with other anti-HBV drugs has not been established. Side effects In clinical practice, toxicity with emtricitabine is unusual. The most common treatment-related adverse events are diarrhea, headache, nausea, and rash. These symptoms are generally mild to moderate in severity, but they caused 1% of clinical trial patients to give up treatment. Skin discoloration, which is typically reported as hyperpigmentation and usually affects either the palms of the hands or the soles of the feet, is reported in less than 2% of individuals and is almost