Herbal remedies are very popular around the world. Many people prefer them to pharmaceuticals because they believe herbs can elicit positive results without serious side effects. However, plants produce a wide variety of chemicals at varying concentrations, and might have a number of effects on your body, both good and bad. Furthermore, since herbal supplements are not evaluated by the FDA for safety or effectiveness, consumers often don’t have ready access to evidence about herbal products. We can’t even be sure that they contain the ingredients that are listed on the label!

St. John’s wort might decrease the effectiveness of birth control pills, and might be unsafe during pregnancy.

One popular herb is St. John’s wort, or Hypericum perforatum. While the scientific evidence is mixed at best, many people believe that St. John’s wort can be used as an antidepressant. However, people often treat themselves with herbal supplements without guidance from a medical doctor or pharmacist — and without knowing whether or not these herbs are safe to use with any medications they might be taking.

Over the millennia, plants have evolved all sorts of powerful chemicals, such as toxins, to defend themselves against insects and other predators. For this reason, we can’t assume that plants only contain inert chemicals that won’t affect us or interact with the chemicals in other drugs and supplements we use. St. John’s wort, in fact, contains chemicals that interfere with other medications. It has been banned in France, and other countries require or are considering warning labels on St. John’s wort products so consumers can be aware of possible drug interactions.

According to the National Institutes of Health, birth control pills are in a “major” risk group for possible drug interactions with St. John’s wort. The “morning-after pill” (emergency contraception) could also be negatively affected by St. John’s wort. An important component of this herb is called hyperforin, a powerful chemical that causes the human body to metabolize certain drugs faster. Birth control pills are one of the many pharmaceuticals thought to be affected by St. John’s wort. One dose of a birth control pill is designed to last for around 24 hours, which is why you need to take your pill at the same time every day. However, if your body metabolizes the pill too quickly, there might not be enough of the drug in your body to last the full 24 hours.

When taken as directed, the birth control pill is more than 99 percent effective. It works by suppressing ovulation — if the ovaries don’t release eggs, there is nothing for a sperm to fertilize, making pregnancy impossible. Even if an egg does manage to squeak through, the Pill also thins the uterine lining, making it more difficult for a fertilized egg to implant in the womb. However, there is still a small risk for unintended pregnancy among users of oral contraceptives, especially when they don’t take their pills properly.

In the medical literature there are several published cases of unintended pregnancies occurring in people who were taking only oral contraceptives and St. John’s wort at the time of conception — but with only a handful of scattered reports, we can’t know whether this relationship is causal or coincidental. However, we do have much more evidence about the possible mechanisms by which St. John’s wort can interfere with birth control pills.

A review of the literature indicates that St. John’s wort might interfere with oral contraception and could cause breakthrough bleeding among people who take the pill. Furthermore, at least three small studies have provided evidence for this relationship:

A study of 18 women found that, while ovulation was not detected in subjects who were taking oral contraceptives and St. John’s wort simultaneously, breakthrough bleeding was more likely to occur. However, the authors pointed out that their subjects still had thinner uterine linings, meaning that even if fertilization did take place, the ovum would be less likely to implant in the uterus to cause a pregnancy.

A study of 12 women also found increased risk of breakthrough bleeding. The authors recommended that people taking oral contraceptives and St. John’s wort at the same time should back up their birth control with condoms.

A study of 16 women found that taking St. John’s wort and birth control pills simultaneously led to a 13 to 15 percent reduction in the the levels of contraceptive hormones circulating in the body. The authors also reported increased breakthrough bleeding, as well as evidence of “probable ovulation” and “possible ovulation.”

Unfortunately, these studies suffer from small sample sizes — although it’s interesting to note that the results point to the same conclusion, that St. John’s wort can interfere with the birth control pill, at the very least by possibly increasing risk for nuisance breakthrough bleeding. Larger studies have not yet been undertaken, however, making it difficult to say for sure how much of a risk St. John’s wort really poses to people taking oral contraceptives to prevent pregnancy.

St. John’s wort is “possibly unsafe” to take during pregnancy, and can have interactions with many other pharmaceuticals as well, highlighting just how potent the chemicals in this herb can be. Aside from birth control pills, St. John’s wort can interact with many other common medications, including:

antidepressants, such as Prozac, Paxil, and Zoloft

antihistamines, such as Claritin, Zyrtec, and Allegra

cyclosporine, which recipients of organ transplants sometimes use

dextromethorphan, a cough medicine

digoxin, a heart medication

immune-suppressing drugs, such as Humira

indinavir and possibly other HIV drugs

irinotecan and possibly other cancer drugs

triptan drugs, used to treat migraines

sedatives, including Ambien, Depakote, and Xanax

seizure-control drugs, such as phenytoin and phenobarbital

theophylline, which treats asthma, emphysema, and chronic bronchitis

warfarin and related anticoagulants

If you suffer from depression that you feel needs treatment, you can consult with a health-care provider to learn about your options. While herbal supplements are not regulated by the FDA and ingredients and dosages can vary from those listed on the label, if you wish to take St. John’s wort but worry about interactions with your birth control, you can learn about other options, such as the non-hormonal copper IUD. You can make an appointment at a Planned Parenthood health center to discuss which birth control method is right for you.