Tenofovir disoproxil fumarate is an antiviral medication primarily used to treat HIV and hepatitis B. It works by inhibiting the reverse transcriptase enzyme, which is essential for the replication of these viruses. This helps to lower the viral load in the body, improving the immune system's function. Additionally, Tenofovir disoproxil fumarate is also used as a preventive measure against HIV infection in high-risk populations, a strategy known as pre-exposure prophylaxis (PrEP). It is usually taken as a daily oral tablet and is well-tolerated by most patients, although some may experience side effects.