- Since 2000, there have been 19 reported cases of contraceptive sabotage.
- Herbs may weaken pills and implants that can cause pregnancy
- Last year, two women who took the herb became pregnant while using the implant.
Drug safety chiefs have issued a new warning about the dangers of mixing the herbal medicine St John’s Wort with some contraceptives.
This herb can weaken the effectiveness of pills or implants, which can lead to unplanned pregnancy.
The Medicines and Healthcare products Regulatory Agency (MHRA) said two women accidentally became pregnant while using the implant late last year.
Experts warn that herbal remedies including St John’s Wort may interfere with contraceptive implants.
The company has received two Yellow Card reports, which are used when there are suspected interactions between drugs, or between drugs and herbal medicines or foods.
“These women experienced unplanned pregnancies after starting to take St John’s Wort,” the spokesman said.
Since 2000, a total of 19 reports of possible interactions between herbs and hormonal contraceptives have been filed.
Four involved implants and 15 involved the pill, 15 of which resulted in unplanned pregnancies.
Since 2000, a total of 19 cases of suspected interactions between St. John’s Wort and contraceptives have been reported, 15 of which involved the pill.
St. John’s Wort, used to treat mild to moderate depression, may also interact with immunosuppressants and lead to transplant rejection.
Oral contraceptive pills and implants already carry warnings in their patient information sheets not to take herbal remedies because they may reduce their effectiveness, and doctors are set to step up their advice to patients.
St. John’s Wort packaging also carries a warning, but unlicensed products and those available online often do not carry the warning information.
Dr Sarah Branch, deputy director of medicines surveillance and risk management at the MHRA, said: “Patient information leaflets for contraceptive pills and implants already contain information about interactions with St John’s Wort, warning that their effectiveness may be reduced.”
“Patients are encouraged to tell their doctors if they are using St. John’s Wort when they are prescribed contraceptives or when they undergo implant surgery.”
“Healthcare professionals should also warn patients about the risk of unintended pregnancy with St. John’s wort when using contraceptives.”
An estimated 10 million Britons regularly take herbal remedies, vitamins and minerals.
In the past, there have been warnings about side effects when some herbal supplements and foods are taken in combination with prescription or over-the-counter medications.
Herbs such as feverfew, ginger and ginkgo biloba may interact with aspirin, which millions of people take in small doses to prevent heart attacks.
Garlic may interfere with the effects of anticoagulants and cyclosporine, an immunosuppressant used to prevent transplant rejection, and valerian, a sedative, may increase the effects of anesthetics.
Other plants and herbs can also interact with medications, such as garlic, which can affect blood thinners.
Herbal products marketed for osteoarthritis may also pose serious risks when taken with prescription medications. For example, glucosamine and chondroitin can affect clotting agents.
Black cohosh may interact with the anti-cancer drug tamoxifen, and cat’s claw may interact with anticoagulants and blood pressure medications.
Studies of grapefruit juice and drug interactions suggest that compounds in grapefruit juice may inhibit enzymes in the intestine that normally break down many drugs.
Drinking a glass of grapefruit juice will provide the greatest blocking effect, which can last for more than 24 hours.
Because the effects are long-lasting, grapefruit juice does not need to be taken at the same time as the medication for an interaction to occur.
Many people are advised to avoid drinking grapefruit juice altogether while taking certain medications, including statins, antihypertensives, psychiatric medications, and Viagra.
