BMJ  2004;329:27-30 (3 July), doi:10.1136/bmj.329.7456.27

Primary care

Interaction of St John's wort with conventional drugs: systematic review of clinical trials

¹ Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada L8N 3Z5, ² Department of Medicine, Mayo Clinic College of Medicine, Rochester, MN 55905, USA, ³ London School of Hygiene and Tropical Medicine, London WC1E 7HU, ⁴ Biopharmaceutics, Watson Laboratories, PO Box 1900, Corona, CA 92878-1900, USA, ⁵ UK Cochrane Centre, Oxford OX2 7LG

Objective To determine the methodological quality of clinical trials that examined possible interactions of St John's wort with conventional drugs, and to examine the results of these trials.

View this table: [in this window] [in a new window]   Characteristics of methods used in 22 reviewed studies

 
Design Systematic review.

Data sources Electronic databases from inception to April 2004, reference lists from published reports, and experts in the field.

Study selection Eligible studies were prospective clinical trials evaluating the pharmacokinetic effect of St John's wort on the metabolism of conventional drugs.

Data extraction Two reviewers selected studies for inclusion and independently extracted data.

Data synthesis 22 pharmacokinetic trials studied an average of 12 (SD 5) participants; 17 trials studied healthy volunteers and five studied patients. Most (17) studies used a "before and after" design; four studies used control groups other than the active group. Three studies randomised the sequence of administration or the participants to study arms or periods; three studies blinded participants or investigators. In 15 trials, investigators independently assayed the herb. Of 19 trials with available plasma data, three found no important interaction (change in area under the curve < 20%) and 17 found a decrease in systemic bioavailability of the conventional drug; in seven studies the 95% confidence interval excluded a decrease of < 20%.

Conclusion Clinicians and patients should beware of possible decreases in the systemic bioavailability of conventional drugs when taken concomitantly with St John's wort.

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