Lamivudine is an antiviral medication primarily used to treat infections caused by the human immunodeficiency virus (HIV) and the hepatitis B virus (HBV). It works by inhibiting the replication of these viruses, helping to reduce their presence in the body and improve the immune system's function. This medication is often prescribed as part of a combination therapy for HIV, meaning it is used alongside other antiviral drugs to enhance effectiveness. Lamivudine is available in various forms, including tablets and oral solutions, and is typically taken once daily for optimal results.