The effect of St John’s wort extracts on CYP3A: a systematic review of prospective clinical trials
Article first published online: 29 SEP 2006
British Journal of Clinical Pharmacology
Volume 62, Issue 5, pages 512–526, November 2006
How to Cite
Whitten, D. L., Myers, S. P., Hawrelak, J. A. and Wohlmuth, H. (2006), The effect of St John’s wort extracts on CYP3A: a systematic review of prospective clinical trials. British Journal of Clinical Pharmacology, 62: 512–526. doi: 10.1111/j.1365-2125.2006.02755.x
- Issue published online: 29 SEP 2006
- Article first published online: 29 SEP 2006
- Received 27 October 2005Accepted12 June 2006Published OnlineEarly29 September 2006
- cytochrome P450;
- herb-drug interactions;
- Hypericum perforatum;
- St John’s wort;
- systematic review
The aim of this systematic review was to assess the quality and outcomes of clinical trials investigating the effect of St John’s wort extracts on the metabolism of drugs by CYP3A.
Prospective clinical trials assessing the effect of St John’s wort (SJW) extracts on metabolism by CYP3A were identified through computer-based searches (from their inception to May 2005) of Medline, Cinahl, PsycINFO, AMED, Current Contents and Embase, hand-searches of bibliographies of relevant papers and consultation with manufacturers and researchers in the field. Two reviewers selected trials for inclusion, independently extracted data and recorded details on study design.
Thirty-one studies met the eligibility criteria. More than two-thirds of the studies employed a before-and-after design, less than one-third of the studies used a crossover design, and only three studies were double-blind and placebo controlled. In 12 studies the SJW extract had been assayed, and 14 studies stated the specific SJW extract used. Results from 26 studies, including all of the 19 studies that used high-dose hyperforin extracts (>10 mg day−1), had outcomes consistent with CYP3A induction. The three studies using low-dose hyperforin extracts (<4 mg day−1) demonstrated no significant effect on CYP3A.
There is reasonable evidence to suggest that high-dose hyperforin SJW extracts induce CYP3A. More studies are required to determine whether decreased CYP3A induction occurs after low-dose hyperforin extracts. Future studies should adopt study designs with a control phase or control group, identify the specific SJW extract employed and provide quantitative analyses of key constituents.