Objective: To estimate the extent to which community pharmacists and health food store clerks provide appropriate advice regarding a drug interaction between oral contraceptives and St. John's wort (SJW).

Design: Cross-sectional study.

Setting: Three community pharmacy chains and three health food store chains in four highly populated counties in California.

Participants: Community pharmacists (n=99) and health food store clerks (n=84).

Intervention: Investigators, posing as consumers, telephoned pharmacists and health food store clerks and asked the following question: "Is there a problem with taking SJW with birth control pills?"

Main outcome measures: Respondents were classified based on their ability to correctly identify the drug interaction (yes or no) and on the overall appropriateness (i.e., the absence of incorrect advice) of their advice. Comparisons were made between men and women respondents and between pharmacists and health food store clerks.

Results: Community pharmacists were more likely than health food store clerks to correctly identify the drug interaction (50.5% versus 10.9%; Xchi(1 df) = 54.32, P < 0.001). Overall, 31.8% of respondents provided inappropriate advice that implied the absence of a drug interaction (26.3% of 99 pharmacists and 34.8% of 184 health food store clerks; Xchi(1 df) = 2.15, P = 0.14). Appropriateness of advice varied significantly among the three pharmacy chains (P < 0.001) and the three health food store chains (P < 0.05). Responses did not differ by gender of respondents (P = 0.18).

Conclusion: Lack of awareness of the potentially serious drug interaction between SJW and oral contraceptives by those who sell these products places the public at risk. Training and education, more comprehensive product labeling, and policies to refer consumers to drug information centers are needed.