Tenovid contains the active substance tenofovir disoproxil fumarate. This active substance is an antiretroviral or antiviral medicine which is used to treat HIV or HBV infection or both. Tenofovir is a nucleotide reverse transcriptase inhibitor, generally known as an NRTI and works by interfering with the normal working of enzymes (in HIV reverse transcriptase; in hepatitis B DNA polymerase) that are essential for the viruses to reproduce themselves. In HIV Tenovid should always be used combined with other medicines to treat HIV infection.