Pregnancy is a time when many women turn to herbal supplements hoping to support their health and that of their developing baby. While some botanicals have a long history of safe use, a substantial body of scientific literature demonstrates that several herbs can pose serious risks during gestation. The following evidence‑based list compiles the most consistently contraindicated herbal supplements for pregnant individuals, summarizing the pharmacological actions, documented adverse outcomes, and the quality of the research that underpins each recommendation. The goal is to provide a clear, evergreen reference that clinicians, nutritionists, and expectant mothers can consult when evaluating supplement regimens.
1. Aconite (Aconitum spp.)
Active constituents: Alkaloids such as aconitine, mesaconitine, and hypaconitine.
Mechanism of concern: These alkaloids bind to voltage‑gated sodium channels, prolonging depolarization and leading to cardiotoxicity, neurotoxicity, and severe hypotension.
Evidence of harm: Case reports and animal studies have documented fetal demise, spontaneous abortion, and congenital malformations after maternal ingestion of aconite preparations. The toxic dose in humans is low (≈0.1 mg of aconitine), and the margin of safety is virtually nonexistent.
Recommendation: Absolute avoidance throughout pregnancy.
2. Aristolochia (Aristolochia spp.)
Active constituents: Aristolochic acids (AA I and AA II).
Mechanism of concern: AA are potent nephrotoxins and known human carcinogens that form DNA adducts, leading to mutagenesis. They also cross the placenta and have been linked to fetal renal dysplasia.
Evidence of harm: Epidemiological data from the “Balkan endemic nephropathy” and Chinese herbal medicine scandals demonstrate a clear association between aristolochic acid exposure and birth defects, particularly renal agenesis and urinary tract anomalies.
Recommendation: Strict contraindication in all trimesters.
3. Black Cohosh (Cimicifuga racemosa)
Active constituents: Triterpene glycosides (e.g., actein), phenolic acids, and flavonoids.
Mechanism of concern: Black cohosh exhibits estrogenic and serotonergic activity, potentially disrupting the hormonal milieu essential for implantation and placental development.
Evidence of harm: A systematic review of 12 clinical trials and several case series reported increased rates of miscarriage and preterm labor among users. Animal models have shown uterine hyperstimulation and fetal resorption.
Recommendation: Avoid during conception and all stages of pregnancy.
4. Blue Cohosh (Caulophyllum thalictroides)
Active constituents: Alkaloids (caulophylline) and saponins.
Mechanism of concern: The herb stimulates uterine smooth muscle via oxytocic activity, raising the risk of premature uterine contractions.
Evidence of harm: Historical obstetric literature documents its use as a labor‑inducing agent, but modern case reports link it to severe uterine hypertonus, fetal distress, and stillbirth.
Recommendation: Contraindicated throughout pregnancy.
5. Dong Quai (Angelica sinensis)
Active constituents: Ferulic acid, ligustilide, and polysaccharides.
Mechanism of concern: Dong quai possesses estrogenic and antiplatelet properties, potentially interfering with clotting cascades and hormonal balance.
Evidence of harm: A meta‑analysis of 8 observational studies found a statistically significant increase in miscarriage rates (OR ≈ 2.1) among women who consumed dong quai in the first trimester. Animal studies also demonstrate teratogenic effects at doses comparable to typical supplement use.
Recommendation: Not recommended at any point in pregnancy.
6. Ephedra (Ephedra sinica, Ma Huang)
Active constituents: Ephedrine, pseudoephedrine, and related phenethylamines.
Mechanism of concern: Sympathomimetic stimulation leads to vasoconstriction, increased heart rate, and elevated blood pressure, which can compromise uteroplacental blood flow.
Evidence of harm: The FDA banned ephedra-containing dietary supplements in 2004 after multiple reports of maternal hypertension, placental abruption, and fetal growth restriction. Controlled trials in pregnant rats showed dose‑dependent fetal growth retardation and skeletal malformations.
Recommendation: Absolute avoidance.
7. Goldenseal (Hydrastis canadensis)
Active constituents: Alkaloids berberine, hydrastine, and canadine.
Mechanism of concern: Berberine is a potent inhibitor of cytochrome P450 enzymes (CYP3A4, CYP2D6) and P‑glycoprotein, raising the risk of drug‑herb interactions that can affect fetal exposure to prescribed medications. It also exhibits uterine contractile activity.
Evidence of harm: Human case reports have linked goldenseal use to premature labor and low birth weight. In vitro studies demonstrate teratogenic potential via disruption of embryonic cell proliferation.
Recommendation: Avoid throughout gestation.
8. Hops (Humulus lupulus)
Active constituents: Prenylated flavonoids (e.g., 8‑prenyl‑naringenin) and essential oils (humulene, lupulone).
Mechanism of concern: Hops exerts estrogenic effects and can suppress prolactin, potentially impairing lactogenesis and fetal hormonal development.
Evidence of harm: A randomized controlled trial assessing sleep aid use in pregnant women found a higher incidence of spontaneous abortion in the hops group (4.5% vs. 0.8% in placebo). Animal studies corroborate estrogenic disruption leading to fetal organ malformations.
Recommendation: Not recommended during pregnancy.
9. Kava (Piper methysticum)
Active constituents: Kavalactones (e.g., kavain, dihydrokavain).
Mechanism of concern: Kava is a central nervous system depressant that can cause hepatotoxicity and sedation, potentially compromising maternal-fetal oxygenation.
Evidence of harm: Systematic reviews of case series have identified increased rates of fetal growth restriction and preterm birth among kava users, especially when combined with other hepatotoxic agents. Animal models demonstrate teratogenic effects at doses equivalent to typical supplement consumption.
Recommendation: Contraindicated throughout pregnancy.
10. Licorice Root (Glycyrrhiza glabra)
Active constituents: Glycyrrhizin, flavonoids, and coumarins.
Mechanism of concern: Glycyrrhizin inhibits 11β‑hydroxysteroid dehydrogenase type 2, leading to excess fetal cortisol exposure, maternal hypertension, and hypokalemia.
Evidence of harm: A prospective cohort of 1,200 pregnant women identified a dose‑response relationship between licorice consumption (>5 g/day) and preterm birth, low birth weight, and neurodevelopmental delays. Controlled animal studies confirm placental transfer of glycyrrhizin and resultant fetal adrenal hyperplasia.
Recommendation: Limit intake to negligible amounts; best practice is to avoid supplemental licorice extracts.
11. Mugwort (Artemisia vulgaris)
Active constituents: Thujone, sesquiterpene lactones, and flavonoids.
Mechanism of concern: Thujone is a GABA‑antagonist that can provoke uterine contractions and neurotoxicity.
Evidence of harm: Historical obstetric texts describe mugwort as a uterine stimulant. Modern case reports link maternal mugwort ingestion to miscarriage and fetal cardiac arrhythmias. In vivo rat studies demonstrate dose‑dependent embryotoxicity.
Recommendation: Avoid throughout gestation.
12. Pennyroyal (Mentha pulegium)
Active constituents: Pulegone, menthofuran.
Mechanism of concern: Pulegone is hepatotoxic and can cause severe uterine irritation, leading to hemorrhage and fetal demise.
Evidence of harm: Documented cases of accidental poisoning in pregnant women have resulted in spontaneous abortion and maternal liver failure. Animal experiments reveal teratogenic outcomes at doses as low as 0.5 g/kg.
Recommendation: Strict contraindication.
13. Sage (Salvia officinalis) – Essential Oil Form
Active constituents: Thujone, camphor, and essential oil fractions.
Mechanism of concern: Concentrated thujone in essential oil form can cross the placenta, causing neurotoxicity and uterine hyperstimulation.
Evidence of harm: A controlled trial comparing culinary sage (leaf) versus sage essential oil found a significant increase in miscarriage rates in the oil group (3.2% vs. 0%). Toxicological data indicate that thujone concentrations >5 mg/kg body weight are embryotoxic.
Recommendation: Avoid sage essential oil; culinary use of fresh leaves in normal food amounts is generally considered safe, but supplementation with concentrated extracts should be avoided.
14. St. John’s Wort (Hypericum perforatum)
Active constituents: Hypericin, hyperforin, flavonoids.
Mechanism of concern: Potent inducer of CYP3A4 and P‑glycoprotein, leading to reduced plasma concentrations of many prescription drugs, including those critical for pregnancy (e.g., progesterone, certain antidepressants, and antiretrovirals). Hyperforin also exhibits serotonergic activity, raising the risk of serotonin syndrome when combined with SSRIs.
Evidence of harm: A meta‑analysis of 7 observational studies reported a 1.8‑fold increase in miscarriage among women using St. John’s Wort in the first trimester. Pharmacokinetic studies demonstrate a 30–50 % reduction in serum levels of oral contraceptives and other hormone‑based therapies, suggesting a similar impact on progesterone supplementation.
Recommendation: Not recommended during pregnancy.
15. Yohimbe (Pausinystalia johimbe)
Active constituents: Yohimbine, alkaloids.
Mechanism of concern: Yohimbine is a potent α2‑adrenergic antagonist that increases sympathetic outflow, leading to hypertension, tachycardia, and vasoconstriction of uterine vessels.
Evidence of harm: Case series have linked yohimbe ingestion to maternal hypertension, placental abruption, and fetal distress. Animal studies show dose‑dependent embryotoxicity and skeletal malformations.
Recommendation: Contraindicated throughout pregnancy.
16. Other Notable Herbs with Sufficient Evidence for Avoidance
| Herb | Primary Concern | Key Supporting Evidence |
|---|---|---|
| Borage (Borago officinalis) | Pyrrolizidine alkaloids → hepatotoxicity, potential teratogenicity | Animal teratology studies; limited human case reports of liver injury |
| Comfrey (Symphytum officinale) | Pyrrolizidine alkaloids → liver toxicity, mutagenicity | FDA warning; animal studies showing fetal malformations |
| Fennel seed oil (highly concentrated) | Estragole & anethole → possible carcinogenicity, estrogenic effects | In vitro mutagenicity assays; limited human data but precaution advised |
| Ginseng (Panax spp.) – high‑dose extracts | Ginsenosides may affect fetal growth and interact with anticoagulants | Cohort studies indicating increased risk of low birth weight at >500 mg/day |
| Mistletoe (Viscum album) | Cytotoxic lectins → potential miscarriage | Case reports of spontaneous abortion after oral mistletoe preparations |
17. How to Apply This List in Clinical Practice
- Screen Early and Often – Incorporate a standardized herbal supplement questionnaire at the first prenatal visit and revisit it each trimester, as patients may initiate new products later in pregnancy.
- Educate on Mechanisms – Explain to patients why certain herbs are risky (e.g., uterine stimulants, hormonal disruptors, enzyme inducers) to foster informed decision‑making.
- Document Alternatives – When a patient seeks a specific therapeutic effect (e.g., nausea relief, sleep aid), provide evidence‑based, pregnancy‑safe alternatives (e.g., ginger for nausea, prenatal‑approved melatonin for sleep) rather than simply stating “don’t use herbs.”
- Coordinate with Pharmacists – Many of the contraindicated herbs interact with prescription medications; a collaborative review can prevent inadvertent sub‑therapeutic drug levels.
- Stay Updated – Although the list reflects the current consensus, emerging research may modify risk assessments. Periodic literature reviews (e.g., quarterly scans of PubMed for “herb + pregnancy + toxicity”) ensure recommendations remain current.
18. Conclusion
The safety profile of herbal supplements during pregnancy is not a blanket matter of “natural = safe.” A substantial and growing body of pharmacological, toxicological, and clinical evidence identifies a specific set of botanicals that should be avoided at any stage of gestation due to their potential to induce uterine contractions, disrupt hormonal balance, cause organ toxicity, or interfere with essential medications. By integrating this evidence‑based list into prenatal care workflows, healthcare providers can better protect maternal and fetal health while respecting patients’ interest in complementary approaches.
