HIV is a virus that attacks the body’s defence against infection and illness – the immune system. If you are living with HIV, you can take drugs to reduce the level of HIV in your body. By taking these anti-HIV drugs, you can slow down or prevent damage to your immune system. By protecting your immune system earlier, you can help prevent health problems occurring now and in the future. These drugs are not a cure, but they can help you stay well and lead a longer and healthier life. Anti-HIV drugs are known as antiretroviral drugs, or antiretroviral therapy (ART).

HIV mainly affects cells in the immune system called CD4 cells. Over many years of untreated HIV infection, the number of CD4 cells drops gradually and the immune system is weakened. It becomes unable to fight infections leading to a condition called AIDS (acquired immune deficiency syndrome). Antiretroviral drugs work by interrupting this process.

Someone living with HIV who isn’t taking HIV treatment may have thousands, or even millions, of HIV particles (‘copies’) in every millilitre of blood, which are replicating all the time. The aim of treatment is to reduce the amount of HIV (known as the ‘viral load’) to very low levels; when this level reaches below 50 copies per millilitre, this is called an 'undetectable' viral load.

To give you the best chance of reducing the amount of HIV in your blood to an undetectable level, your doctor will usually recommend that you take an effective combination of at least three antiretroviral drugs (‘triple therapy’). Once your viral load has become undetectable, your immune system should begin to recover. In addition to keeping you well and preventing damage to your immune system, taking treatment and having an undetectable viral load also prevents HIV from being passed on to someone else during sex.