St. John’s Wort May Not Be Safe During Pregnancy

St. John’s wort is a common name for a plant whose scientific name is Hypericum perforatum. This is an herbal product that is used commonly in managing depression, including peripartum depression. This term applies to a kind of depressive illness that some women experience during the time period just before and after giving birth. As an herbal product, H. perforatum may not be sold in stores purely for the purpose of treating or preventing a medical condition (such as depression). Selling the project for that reason would not be in line with evidence-based medicine, nor with science-based medicine. In the United States, however, due to a law passed during the 1990s, any herbal product may be sold to consumers, until it is proven to cause harm. This is opposite of what happens with a new pharmaceutical medication, which must be proven not to cause harm, and then must be proven to provide a benefit, before it can be sold. Pharmaceutical agents are much safer and much more effective than so-called ‘natural’ products, including St. John’s wort, which is sold in capsules that are labeled as providing 300 milligrams of H. perforatum.

A great deal of uncertainty surrounds the question of whether St. John’s wort is safe to use during pregnancy. Clinical studies have been limited. Results of different studies have conflicted in terms of safety. While some studies suggest that it is safe to consume many times the dosage that is offered in capsules of H. perforatum, there are not enough safety data regarding the use of this product during pregnancy to conclude that it is safe in any amount. It’s also difficult to know what you are getting if you purchase St. John’s Wort, since it is not a pharmaceutical and therefore it is unregulated. A study by Canadian researchers published in 2013 based on testing of numerous herbal products sold in North America found that most of the tested products were of poor quality, with many being contaminated. In the case of St. John’s wort, in particular, certain brands were found to contained filler material in place of the H. perforatum. The filler material is a particular type of herb that causes flatulence (gas) and other intestinal irritation. An old study involving hamsters hints that consuming very high quantities of St. John’s wort could reduce fertility both in females and males. An old study involving hamsters hints that consuming very high quantities of St. John’s wort could reduce fertility your male partner. If the results of either of these studies were confirmed and if the hamster study results were similar in humans, it would be harder for you to become pregnant if you, or your male partner, were using excessive quantities of St. John’s wort.

St. John’s wort is suspected as having potential to trigger uterine contractions, leading to spontaneous abortion (miscarriage). This is based on an old study in Bulgaria involving rabbits and guinea pigs. More research is needed before it can be determined whether such a risk is real. On the other hand, given the Canadian study mentioned earlier showing that herbal products that can be purchased, such as St. John’s wort, often contain substances that are not supposed to be in there, it is a good idea to avoid St. John’s wort during pregnancy. There has been some concern about St. John’s wort possibly causing birth defects, but this concern is based on a very small number of cases. Because St. John’s wort is an herbal product and thus unregulated, however, what you purchase may contain other substances that are not supposed to be in there. There is always a possibility that an herbal product will contain some unknown substance that is dangerous for the fetus. This is a major problem associated with taking substances that are not regulated as medications.

As for long-term consequences of taking St. John’s wort, there are many unknowns, because studies of any effects of herbal products in pregnant women have been limited, due to ethical problems attached to testing such products clinically.

As for safety of St. John’s wort in women who are breastfeeding, a limited number of small studies have been conducted. None of the studies have revealed any side effects in mothers or newborns as a result of the mother taking St. John’s wort. However, studies have generally been of poor quality. More studies, looking at long-term consequences in infants, are needed before St. John’s wort can be recommended for mothers who are nursing.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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