The effect of St John’s wort extracts on CYP3A: a systematic review of prospective clinical trials

Authors

  • D. L. Whitten,

    1. School of Natural and Complementary Medicine, Southern Cross University, Lismore, NSW and
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  • S. P. Myers,

    1. Australian Centre for Complementary Medicine Education and Research, University of Queensland, Brisbane, QLD and Southern Cross University, Lismore, NSW, Australia
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  • J. A. Hawrelak,

    1. School of Natural and Complementary Medicine, Southern Cross University, Lismore, NSW and
    2. Australian Centre for Complementary Medicine Education and Research, University of Queensland, Brisbane, QLD and Southern Cross University, Lismore, NSW, Australia
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  • H. Wohlmuth

    Corresponding author
    1. School of Natural and Complementary Medicine, Southern Cross University, Lismore, NSW and
      Hans Wohlmuth, Southern Cross University, PO Box 157, Lismore NSW 2480, Australia.
      Tel:+61 2 66203159
      Fax:+61 2 66203307
      E-mail:hans.wohlmuth@scu.edu.au
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Hans Wohlmuth, Southern Cross University, PO Box 157, Lismore NSW 2480, Australia.
Tel:+61 2 66203159
Fax:+61 2 66203307
E-mail:hans.wohlmuth@scu.edu.au

Abstract

Aim

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.

Methods

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.

Results

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.

Conclusion

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.

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