Used in the treatment of HIV infection and chronic hepatitis B, it works by inhibiting reverse transcriptase, an enzyme essential for viral replication. It is commonly part of combination antiretroviral therapy (ART) to reduce viral load, slow disease progression, and improve immune function in HIV patients. For hepatitis B, it helps lower the amount of virus in the liver, reducing the risk of liver damage and complications like cirrhosis or liver cancer. Due to the risk of resistance, it is not used alone for long-term hepatitis B treatment. It is available in oral tablet and liquid forms, often combined with other antivirals such as zidovudine or abacavir.