Tenofovir monohydrate is the monohydrate form of tenofovir, a nucleotide reverse transcriptase inhibitor (NRTI). It is a key active pharmaceutical ingredient (API) used in the treatment of human immunodeficiency virus (HIV) infection and chronic hepatitis B virus (HBV) infection. Its chemical name is (R)-9-(2-Phosphonomethoxypropyl)adenine monohydrate. As an antiretroviral drug, tenofovir is a prodrug that is metabolized intracellularly to its active diphosphate form, tenofovir diphosphate. This active metabolite competitively inhibits viral reverse transcriptase and, upon incorporation into the viral DNA chain, acts as a chain terminator, thereby inhibiting viral replication. It is a cornerstone in combination antiretroviral therapy (cART) regimens. Tenofovir monohydrate is primarily formulated as the disoproxil ester prodrug (tenofovir disoproxil fumarate, TDF) or the alafenamide prodrug (tenofovir alafenamide, TAF) to enhance oral bioavailability. It is known for its high barrier to resistance and is widely used globally. Proper handling requires adherence to standard laboratory safety protocols for pharmaceutical actives.