There are six main types (‘classes’) of antiretroviral drugs.

Nucleoside reverse transcriptase inhibitors (NRTIs), and nucleotide reverse transcriptase inhibitors (NtRTIs), which target an HIV protein called reverse transcriptase. These are often all referred to as NRTIs.

In the past, this class of drugs has been referred to as the ‘backbone’ of a first-line HIV treatment combination.

Non-nucleoside reverse transcriptase inhibitors (NNRTIs), which also target reverse transcriptase, but in a different way to NRTIs and NtRTIs. 

Protease inhibitors (PIs), which target an HIV protein called protease.

Entry inhibitors, which stop HIV from entering human cells. There are two types: fusion inhibitors and CCR5 inhibitors. CCR5 inhibitors won’t work in everyone and are very rarely used for first-line treatment. You would have a test to see if this type of treatment would be effective before starting on it. A fusion inhibitor is used only for people who have no other treatment options and is not included in this booklet. 

Integrase inhibitors (INI), which target a protein in HIV called integrase, and stop the virus from inserting itself into the DNA of human cells.

Each class of drug attacks HIV in a different way. Generally, drugs from two (or sometimes three) classes are combined to ensure a combined attack on HIV. Most people start HIV treatment on two NRTI drugs combined with either one NNRTI, one PI or one INI – hence, ‘triple therapy’.