Lamivudine is a synthetic nucleoside analogue and reverse transcriptase inhibitor (NRTI) with the chemical formula C₈H₁₁N₃O₃S. It is commonly used as a reagent in pharmaceutical research and synthesis for antiviral drug development. Therapeutically, it is used in the treatment of HIV infection and chronic hepatitis B, where it works by inhibiting the reverse transcriptase enzyme, essential for viral replication. It is commonly prescribed as part of combination antiretroviral therapy (cART) to reduce the amount of virus in the body, helping to improve immune function and slow disease progression. In hepatitis B, it helps lower viral load and reduce liver damage. Due to its oral bioavailability and relatively favorable safety profile, it is widely used in both adult and pediatric populations. However, long-term use may lead to viral resistance, particularly in hepatitis B, so it is often used in combination with other antiviral agents for better efficacy.