Tenofovir disoproxil fumarate is an antiviral medication primarily used to treat HIV and chronic 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 and improve immune function. This medication is often prescribed as part of a combination therapy to enhance its effectiveness. It is available in tablet form and is usually taken once daily. Common side effects may include nausea, diarrhea, and headache, but serious side effects can occur, so regular monitoring by a healthcare provider is important.