- Since 2000, 19 cases of interference with contraceptives have been reported.
- Herbs weaken the effects of pills and implants that can cause pregnancy
- Last year, two women who took the herb became pregnant while using implants.
Medicines safety chiefs have issued renewed warnings about the dangers of mixing the herbal remedy St John’s wort with some contraceptive pills.
This herb can make the pill or implant less effective and lead to an unplanned pregnancy.
Two women accidentally became pregnant while using implants late last year, the Medicines and Healthcare products Regulatory Agency (MHRA) said.
The company received two yellow card reports, which are used for suspected interactions between drugs or when drugs are combined with herbal medicines or even food.
“These women began taking St. John’s wort and subsequently had unplanned pregnancies,” the spokesperson said.
Since 2000, a total of 19 reports of suspected interactions involving herbal and hormonal contraceptives have been filed.
4 cases were due to implants and 15 cases were due to the pill, 15 of which resulted in unplanned pregnancies.
St. John’s wort is taken for mild to moderate depression, but it can also interact with immunosuppressants and cause transplant rejection.
Oral contraceptive pills and implants have a warning on the patient information sheet not to take herbal medicines due to the risk of decreased effectiveness. Physicians are reinforcing their advice to patients.
St. John’s wort packets also contain a warning, but some unlicensed products and those available online often do not include that information.
Dr Sarah Branch, Deputy Director of Medicines Vigilance 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, which could reduce their effectiveness. “We are warning that there is a sexual nature.”
“Patients are encouraged to tell their doctor if they are using St. John’s wort when they are prescribed contraceptives or receive an implant.
“Health care professionals should also warn patients about the risk of unintended pregnancy associated with St. John’s wort when using contraceptives.”
An estimated 10 million Britons regularly take herbal remedies, vitamins and minerals.
Previous warnings have been issued about the side effects of combining some herbal supplements and foods with prescription and over-the-counter medications.
The herbs feverfew, ginger, and ginkgo can interact with aspirin, which millions of people take in low doses to prevent heart attacks.
Garlic can interfere with the effects of anticoagulants and cyclosporine, an immunosuppressive drug that prevents transplant rejection, and sedative valerian can potentiate the effects of anesthetics.
Herbal products sold over the counter for osteoarthritis can also pose serious risks when combined with prescription medications. For example, glucosamine and chondroitin can affect clotting agents.
Black cohosh may interact with the cancer drug tamoxifen, and cat’s claw may interact with clotting agents and blood pressure medications.
Research on grapefruit juice and drug interactions suggests that compounds in grapefruit juice may block enzymes in the intestines that normally break down many drugs.
One glass of grapefruit juice provides the greatest blocking effect, and the effects can last for more than 24 hours.
Because the effects last for a very long time, it is not necessary to take grapefruit juice at the same time as the drug for an interaction to occur.
Many people are advised not to drink grapefruit juice at all while taking certain medications, such as statins, antihypertensives, psychotropic drugs, and Viagra.
