Herbs are commonly consumed by pregnant and breast-feeding women, possibly because they believe that “natural products” are safer than drugs. However, even though some have been available for hundreds or thousands of years, little is known about their effects on the embryo, fetus, newborn, or nursing infant. Moreover, as unregulated products, the concentration, contents, and presence of contaminants cannot be easily determined. Detailed reviews of the 22 most commonly used herbs discussed here can be found in “Drugs in Pregnancy and Lactation,” Briggs GG, Freeman RK, 10th ed., Philadelphia: Wolters Kluwer Health, 2014).
In the following discussions, dose, one of the two key factors that determine the risk of developmental toxicity (abnormal growth, structural anomalies, functional and/or neurobehavioral deficits, or death), is rarely reported. In addition, all herbs contain multiple chemical compounds, few of which have been studied during pregnancy or lactation. Thus, with few exceptions, a woman who takes an herb in pregnancy should be informed that the risk to her developing baby is unknown.
Six herbs are considered contraindicated in pregnancy: arnica, black seed /kalanji, blue cohosh, feverfew, salvia divinorum, and valerian.
• Arnica. The dried flowers, and sometimes the roots and rhizomes, are the parts of this perennial plant that are used topically for their anti-inflammatory and analgesic effects. There is no clinical evidence to support this use. Occasional topical use probably represents a low risk, but absorption may occur when it is applied to broken skin. The Food and Drug Administration has classified arnica as an unsafe herb and, when used orally, it is considered a poison. It is a uterine stimulant and an abortifacient. Nevertheless, in homeopathic formulations, it has been promoted for use before and during labor for internal and external bruising of the mother and newborn. In Italy, it is one of the top 10 herbs taken by women (Pharmacoepidemiol. Drug Saf. 2006;15:354-9).
• Black seed/kalanji. This herb has been used for thousands of year as a medicine, food, or spice. Because of this, it is unlikely that it causes teratogenesis. Nevertheless, its use to stimulate menstruation and its potential contraceptive properties suggest that it is contraindicated in pregnancy.
• Blue cohosh. Some of the components of this herb have been shown to be teratogenic and toxic in various animal species, so it should be avoided in the first trimester. The herb has uterine stimulant properties that are used by nurse-midwives to stimulate labor. Blue cohosh was the most frequently used herbal preparation for this purpose. However, some sources believe that the potential fetal and newborn toxicity may outweigh any medical benefit (“PDR for Herbal Medicine,” 2nd ed., Montvale, N.J.: Medical Economics, 2000:109-10; “The Review of Natural Products,” St. Louis, MO: Facts and Comparisons, 2000).
• Feverfew. This herb has been used for labor, menstrual disorders, potential miscarriage, and morning sickness; as an abortifacient; and for several other indications. Because of its antipyretic properties, it has been known as “medieval aspirin.” The doses used for these indications have not been quantified. Because of its emmenagogic (capable of provoking menstruation) activity, the herb should not be used in pregnancy.
• Salvia divinorum. This herb has hallucinogenic effects and is used in certain regions of Mexico for healing and divinatory rituals. It is also thought to have antidiarrheal properties. The herb is either smoked or chewed, or its juices are ingested. When taken orally, systemic effects are dependent upon absorption across the oral mucosa as the active ingredient is destroyed in the GI tract. Persistent psychosis has been observed in people who smoked the herb, so it is contraindicated in pregnancy.
• Valerian. A large number of preparations containing valerian are available. It has been used as a sedative and hypnotic for anxiety, restlessness, and sleep disturbances, as well as several other pharmacologic claims. Because of the risk of cytotoxicity in the fetus and hepatotoxicity in the mother, the herb should be avoided during gestation.
For the remaining 16 herbs, small, infrequent doses probably cause no harm to the mother, embryo, fetus, or newborn. Nevertheless, as noted below, some of these herbs are best avoided during pregnancy.
• Chamomile. Excessive use of this herb should be avoided because it is thought to have uterine stimulant, emmenagogic, and abortifacient properties. Although controversial, some nurse-midwives prescribe chamomile teas for the treatment of morning sickness. Because the plant sources of the herb contain coumarin compounds, ingesting chamomile by pregnant women with coagulation disorders is a concern. However, the herb has been used for thousands of years, so the risk of harm, at least from occasional use, must be very rare.