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Virtually no medicinal herb has been established as safe in pregnancy or breast-feeding, and even herbs that might seem safe because of their wide use in cooking could cause problems when they are taken in the form of highly concentrated extracts. For example, based on food use, it is unlikely that cookedgarlic presents much risk; however, garlic supplements contain certain rather potent and potentially toxic ingredients present only in raw garlic. Few people eat large quantities of raw garlic on a regular basis, and therefore there is no long history of use to reassure us.
Some herbs are definitely known to be toxic in pregnancy, such as blue cohosh and pennyroyal. Other herbs that are traditionally regarded with caution during pregnancy include andrographis, boldo, catnip, essential oils, feverfew, juniper, licorice, nettle, red clover, rosemary, shepherd's purse, and yarrow, along with many others.1
Modern research has raised concerns about many other herbs, as well. For example, the herb chasteberry has shown a theoretical potential for inhibiting milk supply. In addition, herbs with estrogen-like properties make scientists worry about possible effects on the fetus; these include soy, isoflavones, red clover, flaxseed, lignans, and hops.
Further health concerns exist with traditional Chinese herbal combinations and Ayurvedic herbal combinations. These products have been found on occasion to contain toxic heavy metals, poisonous herbs, or unlabelled prescription drugs.4,11 For example, in one case report, a brain-damaged child born to a mother using an Ayurvedic formula was found to have the highest bloods levels of lead ever recorded in a living newborn.11 Analysis of the formula revealed a very high lead content, along with toxic levels of mercury. In general, it is probably accurate to say that noherb can be regarded as definitely benign.2
Supplements that are essential nutrients, such as vitamins, generally have a known maximum safe intake level during pregnancy and nursing, and these are discussed in the relevant articles in this database. However, other supplements that are not essential nutrients are in much the same position as herbs, and they could conceivably cause harm. For example, the supplement conjugated linoleic acid (CLA) appears to reduce the fat content of breast milk, with potentially harmful effects on the nursing infant,3chitosan may cause impaired nutrient absorption, and at times may contain arsenic. (Contamination with toxic substances is also a real possibility with one nutrient supplement: certain calcium supplements have been found to contain high levels of lead.)
Nonetheless, many herbs and supplements have a high enough safety factor that researchers have felt comfortable giving them to pregnant women. For more information on a particular herb or supplement, see its entry in the Herbs & Supplements database.
1. Newall C, Anderson LA, Phillipson JD. Herbal Medicines: A Guide for Health-Care Professionals. London, England: Pharmaceutical Press; 1996:15-16.
2. Ernst E. Herbal medicinal products during pregnancy: are they safe? BJOG. 2002;109:227-235.
3. Masters N, McGuire MA, Beerman KA, et al. Maternal supplementation with CLA decreases milk fat in humans. Lipids. 2002;37:133-138.
4. Boyer EW, Kearney S, Shannon MW, et al. Poisoning from a dietary supplement administered during hospitalization. Pediatrics Electronic Pages. 2002;109:E49.
5. Florkowski CM, Elder PA, Lewis JG, et al. Two cases of adrenal suppression following a Chinese herbal remedy: a cause for concern? N Z Med J. 2002;115:223-224.
6. Cronin AJ, Maidment G, Cook T, et al. Aristolochic acid as a causative factor in a case of Chinese herbal nephropathy. Nephrol Dial Transplant. 2002;17:524-525.
7. Misidentified Herb Causes Serious Problems for Users of Imported Chinese Herbal Medicine. Kampo Today [serial online]. 1998;3. Available: http://www.tsumura.co.jp/english/kthp/3-1-03.htm. Accessed November 20, 2002.
8. Ernst E. Adulteration of Chinese herbal medicines with synthetic drugs: a systematic review. J Intern Med. 2002;252:107-113.
9. Verucchi G, Calza L, Attard L, et al. Acute hepatitis induced by traditional Chinese herbs used in the treatment of psoriasis. J Gastroenterol Hepatol. 2002;17:1342-1345.
10. Chan TY. Incidence of herb-induced aconitine poisoning in Hong Kong: impact of publicity measures to promote awareness among the herbalists and the public. Drug Saf. 2002;25:823-828.
11. Tait PA, Vors A, James S, et al. Severe congenital lead poisoning in a preterm infant due to a herbal remedy. Med J Aust. 2002;177:193-195.
12. Navarro-Peran E, Cabezas-Herrera J, Garcia-Canovas F, et al. The antifolate activity of tea catechins. Cancer Res. 2005;65:2059-2064.
Last reviewed December 2015 by EBSCO CAM Review Board Last Updated: 12/15/2015