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Herbal medicine during pregnancy

Herbal and other supplements are marketed cleverly, based explicitly or implicitly on the naive notion that ‘natural’ means ‘safe’. For many patients, this fallacy is as compelling as it might be worrying to their GPs.

One group of individuals particularly likely to be taken in by this ploy is pregnant women. As soon as a woman finds out she is expecting, she thinks twice about taking ‘dangerous chemical drugs’. This cautious attitude is, of course, laudable but it also makes pregnant women easy victims for the ‘natural’ supplements industry.

The situation is made worse by the fact that many midwives are besotted with the wonders of alternative medicine and encourage their patients to try this or that herbal remedy.1 As a result, a large proportion of pregnant women use such treatments, often without telling their GP or healthcare team.2

Few people seem to question the assumption that natural equals safe. Yet the facts are clear and well documented. Herbal medicine, for instance, can cause harm through:

  • the toxic effects of one or more ingredients in the plant3
  • interactions with prescription drugs4
  • contamination with heavy metals5
  • adulteration with potent prescription drugs6
  • replacing (more) effective treatments for serious conditions.

Even though the potential for causing harm is so very obvious, there is little systematic research in this area. We therefore have to rely mostly on case reports that suggest adverse effects of herbal remedies do occur and can be serious.7,8,9

Herbalists and other interested parties tend to play down these risks and argue that, if there were a real problem, we would have long been aware of it; and anyway, herbal medicine is certainly miles safer than conventional drugs. These notions usually calm down worried mothers-to-be, but they are hardly convincing arguments: harm can be delayed in such a way that it is far from straightforward to identify the cause, and a fair comparison of the safety of drugs with that of herbs would require similar pharmacovigilance for both.

I would argue that safety is too important to be left to conjecture. What we need is data. For most herbal remedies, we have no evidence to show that they are safe for pregnant women. Until positive evidence emerges, the principle of primum non nocere – ‘first, do no harm’ – leaves us little choice but to consider the use of herbal and other ‘natural’ supplements during pregnancy with healthy scepticism.

Professor Edzard Ernst is the emeritus professor of complementary medicine at the Peninsula Medical School, University of Exeter


1 Ernst E, Watson LK. Midwives' use of complementary/alternative treatments. Midwifery 2011;Oct 18.

2 Broussard CS, Louik C, Honein MA et al. National Birth Defects Prevention Study. Herbal use before and during pregnancy. Am J Obstet Gynecol. 2010;202:443.e1-6. Epub 2009 Dec 29.

3 Ernst E. Harmless herbs? A review of the recent literature. Am J Med 1998;104:170-8.

4 Izzo AA, Ernst E. Interactions Between Herbal Medicines and Prescribed Drugs: An Updated Systematic Review. Drugs 2009;69:1777-98.

5 Ernst E, Thompson Coon J. Heavy metals in traditional Chinese medicines: a systematic review. Clin Pharmacol Ther 2001;70:497-504.

6 Ernst E. Adulteration of Chinese herbal medicines with synthetic drugs: a systematic review. J Internal Med 2002;252:107-13.

7 Ernst E. Serious adverse effects of unconventional therapies for children and adolescents: a systematic review of recent evidence. Eur J Pediatr 2003;162:72-80.

8 Chuang CH, Doyle P, Wang JD et al. Herbal medicines used during the first trimester and major congenital malformations: an analysis of data from a pregnancy cohort study. Drug Saf 2006;29:537-48.

9 Marcus DM, Snodgrass WR. Do no harm: avoidance of herbal medicines during pregnancy. Obstet Gynecol 2005;105(5 Pt 1):1119-22.

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