Atripla contains three active substances: efavirenz, which is a non-nucleoside reverse transcriptase inhibitor (NNRTI); emtricitabine, which is a nucleoside reverse transcriptase inhibitor; and tenofovir disoproxil, which is a ‘ prodrug ’ of tenofovir, meaning that it is converted into the active substance 7 Westferry Circus, Canary Wharf, London E14 4HB, UK Tel.