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


METHODS
Systematic review.


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


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


METHODS
Two reviewers selected studies for inclusion and independently extracted data.


RESULTS
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%.


CONCLUSIONS
Clinicians and patients should beware of possible decreases in the systemic bioavailability of conventional drugs when taken concomitantly with St John's wort.
Mills
Edward
E
Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada L8N 3Z5. millsej@mcmaster.ca
Montori
Victor M
VM
Wu
Ping
P
Gallicano
Keith
K
Clarke
Mike
M
Guyatt
Gordon
G
D019540:Area Under Curve; D002986:Clinical Trials as Topic / Q000592:standards; D041743:Herb-Drug Interactions; D006801:Humans; D020902:Hypericum / Q000378:metabolism*; D015588:Observer Variation; D010599:Pharmacokinetics