HIV drug resistance occurs when antiretroviral drugs lose their ability to block the reproduction of the HIV virus within the body. There are several factors which contribute to the accumulation of drug-resistance during antiretroviral therapy. They include:

• Poor treatment adherence (not taking medications as or when recommended).
• Poor absorption (this can happen as a result of not taking medication with food or when diarrhea and vomiting is experienced and drugs are expelled from the gut too quickly).