Blue cohosh (Caulophyllum thalictroides)

Free to every reader. The safety section of every monograph is open to everyone, signed in or not. In an emergency call 000. For poisoning, call the Poisons Information Centre on 13 11 26.

15. Safety

Red flags (Medicine, reviewed 2026).

1. Pregnancy, at any stage, including to induce or assist labour: do not use. Neonatal heart attack and heart failure, perinatal stroke and hypoxic brain injury have been reported after maternal use in late pregnancy, one of its constituents is teratogenic in embryo culture, and a root extract disrupts heart and face development in fish embryos [17,18,22,28]. Evidence: case reports (very low certainty for cause) with consistent preclinical toxicity; no study shows safety.
2. Breastfeeding and trying to conceive: do not use [13,18,31]. Evidence: manufacturer and practitioner-text contraindications; no human data.
3. Children: keep the plant and the seeds away from them. Children have been poisoned by eating the bright blue seeds [14].
4. Signs of nicotinic poisoning after a blue cohosh preparation (fast heart, sweating, abdominal pain, vomiting, muscle twitching or weakness, high blood pressure, fits, laboured breathing) are an emergency: call 000, or the Poisons Information Centre on 13 11 26 for advice [14,18,30].
5. Blue cohosh is a different plant from black cohosh (Actaea racemosa), and practitioner texts warn against confusing them [8]; one of nine US products sold as blue cohosh contained black cohosh, and two were homoeopathic sugar tablets (section 10) [25]. Check the botanical name and plant part on the label.

Adverse effects from trials. None; there are no trials.

Case reports and causality. The primary reports are on the full-text request list; the accounts below are as given in the full-text library books and reviews cited. Causality is read on the WHO-UMC scale by Medicine (Dr Eleanor Whitcombe), from those accounts; it will be re-read when the primary reports arrive. Certainty that blue cohosh causes these outcomes, taken together: very low (GRADE; case reports only, no product analysed, co-exposures in two).

Midwives in the 1999 US survey also reported nausea, more meconium-stained fluid and transient fetal tachycardia with blue and black cohosh, without separating the two herbs [16,18]. Trickey records that these reports were formally disputed, citing a 1997 reply to the New Zealand case, on the ground that the toxic effects would need much higher doses than those reported, and advises caution in pregnancy until the question is settled [15]. That dispute does not weaken the red flag: the reports are few and uncontrolled, but their outcomes are grave and no study shows safety.

Toxicology. Nicotinic toxidrome with high doses: nausea, vomiting, headache, dizziness, fasciculations, seizures, tachycardia, tachypnoea and hypertension, progressing to respiratory failure, with muscarinic signs (salivation, bronchorrhoea, slow heart) possible; the saponin fraction is credited with vasoconstriction, hypertension and vaso-occlusion; the review notes that death can follow severe untreated poisoning [30]. Evidence: a clinical toxicology review extrapolating from nicotine and the case reports, not from measured blue cohosh overdoses. The powdered root irritates mucous membranes [14], and the dust provokes sneezing [11]. Developmental and mitochondrial toxicity in section 14 [22,23,28]. No repeat-dose animal study of the root was found.

Contraindications.
Each line carries its sources and the kind of evidence behind it.

• Pregnancy: contraindicated [13,19,45]; Mills and Bone’s pregnancy table lists it as contraindicated "except to assist with birth" [18]; Hechtman’s pregnancy table, taken from Romm, gives AHPA class 2b and Mills and Bone category D, "possibly safe for short-term use during labour only, and with proper monitoring of fetal heart tones", while Hechtman’s own text says it "is no longer recommended for use in pregnancy" [16]. Trickey (2003) still gave a first-trimester dose, not more than 0.25–0.5 mL three times a day, always with Viburnum prunifolium and only on a trained herbalist’s prescription [15]; that advice is superseded by the current manufacturer contraindication and is not followed here. AIP adopts the strictest position, with no exception for labour (red flag 1). Evidence: case reports (very low certainty) with consistent embryo-culture and fish-embryo toxicity; practitioner consensus.
• Lactation: contraindicated [13,18]; LactMed finds no data on use while breastfeeding, notes the gastrointestinal and cardiovascular toxicity, and reports that most sources recommend strongly against it [31]. Evidence: no human data; precaution from toxicity.
• Women trying to conceive: contraindicated [13]. Evidence: manufacturer label, with antifertility and developmental effects in animals and embryo culture (section 14); no human data.
• Cardiovascular disease, hypertension or angina: avoid. Barnes notes that it is not known whether excessive doses raise blood pressure through N-methylcytisine, and an older British compendium warns of interference with angina therapy [14,20]; the caulosaponin constricted coronary vessels in animals [14]. Evidence: pharmacology and theory; no human study. AIP makes this an avoid rather than a caution because the toxicity would fall on the heart.
• Gastrointestinal inflammation: may irritate [14]. Evidence: reference-text statement.

Herb–drug interactions.

No clinical interaction study or pharmacokinetic interaction study exists, so no interaction is graded above theoretical. MediHerb refers prescribers to its separate herb–drug interaction chart for this extract [13].

Children and older people. No data. Not for children: no source read gives a dose for children, and children have been poisoned by the seeds (red flag 3). This is AIP’s position, from the absence of data. Older people: no data; those with heart disease or high blood pressure should avoid it (see contraindications).

Overdose. There is no antidote. Treat as nicotinic poisoning: cardiovascular and respiratory support, fluids and vasopressors for low blood pressure, benzodiazepines for seizures, atropine for muscarinic signs, antihypertensives for a hypertensive crisis; haemodialysis is unlikely to help [30]. In Australia, call 000 in an emergency; the Poisons Information Centre is on 13 11 26.

Australian safety record. Checked by Medicine in September 2026. The TGA website search and the DAEN medicines search both returned a bot-protection challenge page to our tools, so neither could be read that day; a web search restricted to the TGA site returned no TGA page naming blue cohosh or Caulophyllum. That is not proof of absence. No TGA safety alert, advisory or recall for blue cohosh was found in any source read, and none is cited by the Australian practitioner texts [13,15,16,19]. The DAEN query and a TGA alert search by hand stay on the list in section 18; the result, nil or not, is to be added here. Blue cohosh is a permitted ingredient with no specific requirements (section 0.1) [2]; no ARTG product carries its name [51].

Referral. Anyone considering blue cohosh should consult a degree-qualified herbalist with competencies and adequate training in pharmacognosy, and should not use it at all if pregnant, breastfeeding or trying to conceive.