There are approximately 25 HIV ‘antiretroviral’ drugs that have been approved for the treatment of HIV infection.  They are used in combination; typically 3 or more drugs from 2 or more different classes, with the aim of suppressing the virus to very low, ideally undetectable, levels in the blood.  This prevents the virus from depleting the immune cells that it preferentially attacks (CD4 cells) and prevents or delays illness and death. The use of combination antiretroviral therapy has dramatically reduced the levels of illness and death among those infected with HIV. A recent study found that the number of deaths due to HIV/AIDS in 12 high-income countries was reduced by 85% following the introduction of combination therapy.