Coadministration is contraindicated in the European SPC (but no longer in the US Prescribing Information) for efavirenz as St John's wort is expected to substantially decrease efavirenz concentrations and may result in sub-optimal levels. If a patient is already taking St John's wort, stop St John's wort, check viral levels and if possible efavirenz levels. Efavirenz levels may increase on stopping St John's wort and the dose of efavirenz may need adjusting. The inducing effect of St John's wort may persist for at least 2 weeks after cessation of treatment. However, a recent study suggests a low risk of a clinically relevant pharmacokinetic interaction with low-hyperforin formulations (<1 mg/day) of St John’s Wort (hyperforin is the constituent responsible for induction of CYPs and P-gp). Coadministration may be considered with St John’s Wort formulations that clearly state the hyperforin content and which have a total daily hyperforin dose of 1 mg or less.