In pre-clinical animal studies of darunavir (Prezista), no particular safety concerns emerged. In the POWER studies, side-effects were mild to moderate, and were similar across all doses of darunavir. The commonest side-effects were diarrhoea, nausea and headache, but these were less common in the darunavir arms than in patients taking the comparator protease inhibitor^[1][2]. Around 7% of patients also experienced skin rash, which was serious in a few cases.