Tenofovir Disoproxil Fumarate (TDF) is an antiviral medication primarily used to treat HIV and chronic hepatitis B. It belongs to a class of drugs known as nucleotide reverse transcriptase inhibitors (NRTIs), which work by blocking the reverse transcriptase enzyme, preventing the virus from replicating in the body. TDF is often prescribed as part of a combination therapy to enhance its effectiveness and reduce the risk of drug resistance. It is available in tablet form and is typically taken once daily. Common side effects may include nausea, diarrhea, and headache, but serious side effects can occur, necessitating regular monitoring by a healthcare provider.