St John's wort causes a marked reduction in the
serum levels of indinavir, which may result in HIV treatment failure. Other
protease inhibitors are predicted to interact similarly.
The advice of the CSM in the UK is that patients taking
protease inhibitors should avoid St John's wort, and that anyone already taking both should stop the St John's wort and have their HIV
RNA viral load measured. The manufacturers also note that
protease inhibitor levels may increase on stopping St John's wort, and the dose may need adjusting. They note that the inducing effect may persist for up to 2 weeks after stopping treatment with St John's wort.