While pregnancy is a healthy condition, not a pathological one, it does require special consideration for medical treatment. The same is true to some extent for breastfeeding mothers. The obvious reason is that medications and other interventions might have negative effects on the developing child or newborn. It is therefore standard of care that any woman of childbearing age is asked about the possibility that they might be pregnant, and essentially treated as if they are pregnant unless we know they are not (using effective prophylaxis is adequate reassurance). Any medication that is not known to be safe in pregnancy is also treated with caution, and not used if it can be avoided.

Some pregnant women have medical conditions that need to be treated, however, and themselves might pose a risk to their child. Therefore a risk vs benefit approach is taken for any possible treatment, and when multiple options are available, greatest priority is given to the interventions that are safest for the pregnancy.

But then, in many cases, all this caution and calculus are thrown out the window when it comes to use of herbal products and dietary interventions. Most patients do not even disclose their use of herbal products to their doctors unless specifically asked. Literally centuries of marketing have created an unearned health halo around any product arbitrarily labeled as “natural” (the appeal to nature fallacy). In the US and elsewhere the herbal product industry has largely been deregulated, leaving few consumer protections in place. The lines between food and medicine have also been deliberate blurred, with so-called “nutraceuticals” and alleged “superfoods”.

There are good reasons for concern, however, that “natural” products, and even some foods, do present a potential risk to an unborn child. A recent review of the relevant literature finds that there is evidence substances derived from foods and herbal products can cross the placental barrier. Somethings this only occurs after they have been metabolized by intestinal flora. This means that we need to study not only the products themselves, but all downstream metabolites (which is common practice in pharmacology).

This is yet more evidence that the double standard between herbs and drugs is a false one, based upon the flawed premise of the appeal-to-nature fallacy. Co-author Andrew Machpherson summarizes the implications of their research:

Although plants products are ‘natural’ substances, they are always so-called xenobiotic substances that are foreign to the body and should be handled very carefully, especially when pregnant women take plant-based products in large quantities.

The use of herbal products during pregnancy is difficult to estimate because of low levels of reporting. Estimates vary from 4 to 69%. A 2010 study form the US estimated the use at 5.8%, but this is likely an underestimate. Even at the low end of the estimate range, this still represent a significant use for the pregnant population.

This is also not just a theoretical concern. A 2015 literature review found extensive evidence of harm from herbal product use during pregnancy. The authors warn:

While definitive data emerge, all herbal products should be viewed with caution, although there are no explicit warnings that herbals should not be used during pregnancy and lactation.

They key in on the problems. First, we don’t really know what the risk is. We have evidence for potential harm, and we have essentially case reports of actual harm. But we lack the kind of systematic safety research that is required for medications. This highlights the second problem they identify – lack of explicit warnings. This in turn is due to the double standard, both in popular belief and reflected in regulations. Herbal products are largely thought of as “natural” which somehow makes them magically safe. It is worth pointing out that many things found in nature – such as botulinum toxin and the death’s cap mushroom – are extremely toxic.

As I have been pointing out since the beginning of this blog, herbs are drugs. When an herbal product is taken in concentrated form for alleged pharmaceutical (as opposed to nutritional) effects, that is a drug. Herbs have drug-drug interactions, they have to be metabolized, they can cause toxicity, and they can cross the placental barrier or be excreted in breast milk.

However, we allow the supplement industry to falsely tell consumers not to worry about their herbal products, because they are natural, or because they are “nutraceuticals”. We allow them to self-regulate when it comes to product purity and fidelity. There is no standardization of dosage. We largely lack the kind of specific information we demand for pharmaceuticals, such as pharmacodynamics and pharmacokinetics.

Herbs need to be thought of for what they are – unregulated, poorly studied drugs with largely unknown properties. Further, they are marketed with health claims that are not substantiated by research. In fact, they are often marketed with claims that have already been shows not to be true. As I have pointed out before:

One by one rigorous clinical trials have shown that the most popular herbal remedies do not work as advertised: ginkgo biloba for memory and dementia, echinacea for cold and flu, glucosamine and chondroitin for arthritis, black cohosh for hot flashes, and saw palmetto for the prostate and urinary tract.

Further, the popular antioxidants are also largely useless, and may even be harmful in some cases. We are essentially allowing an entire industry to gaslight the public, to make false claims, and to be free of any burden of having to prove safety or efficacy. The results are predictable.

Pregnancy does present a special case, and woman who are pregnant, trying to become pregnant, or may be pregnant, should exercise extreme caution when it comes to any herb, supplement, extreme diet, or alleged “superfood”. Taking large amounts of anything should be avoided. The risk vs benefit analysis is pretty clear – there is potential risk, and no proven benefit.


Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.