Nelfinavir is primarily used as an antiretroviral medication in the treatment of HIV infection. It works by inhibiting the protease enzyme, which is essential for the replication of the virus. This helps to reduce the viral load in the body and improves the immune system function. It is often prescribed as part of a combination therapy with other antiretroviral drugs to enhance its effectiveness and prevent the development of drug resistance. Additionally, nelfinavir has been explored in research for its potential anticancer properties, particularly in inhibiting pathways involved in tumor growth and survival. However, its use in cancer treatment remains experimental and is not yet standard practice.