St. John's Wort May Counteract Birth Control Pill: Sweden

St. John's Wort May Counteract Birth Control Pill: Sweden

STOCKHOLM--The Swedish Medical Products Agencyposted on its Web site two reports of women becoming pregnant because theircontraceptive pills' effectiveness was adversely affected by their use of St.John's wort products. According to a story on Reuters, the country will bestrengthening its existing warning about the use of St. John's wort while usingprescription medications.

In 1999, researchers raised initial concerns about St. John's wort's abilityto influence a particular metabolic pathway, making drugs move through the bodymore quickly than normal. At that time, the media raised an alert about thepossibility of St. John's wort influencing birth control and the Food and DrugAdministration (FDA) issued a warning to doctors about potential interactionswith both HIV treatment drugs and other drugs, including birth control. At thetime, many industry members had problems with these conclusions. "There areno specific studies showing that St. John's wort affects blood levels or theeffectiveness of oral contraceptives," Rob McCaleb, president of the HerbResearch Foundation, told INSIDER.

Last year, researchers found that St. John's wort appears to boost P-glycoproteinactivity, a "drug transporter" in the intestines, making drugs morelikely to be excreted than absorbed by the body. One researcher told ReutersHealth that a one-time use would not affect drug uptake, but that chronic usecould do so.

In the Swedish case reports issued Feb. 4, two women (ages 31 and 28) becamepregnant while taking the pill and St. John's wort. The report noted that St.John's wort has been shown to only moderately induce the enzyme that metabolizesthe pill. "To sum up, natural medicine containing St. John's wort canresult in a risk for reduced plasma concentrations and a decreased clinicaleffect of the Pill," MPA reported. (The report is online in Swedish at www3.mpa.se.) "The inducing effect can remain for at least two weeks afterstopping use of St. John's wort. This information has now been introduced in theproduct summary of the Pill."