Black cohosh

Is black cohosh safe?

For most women using a reputable product for menopausal hot flushes for up to six months, yes. Trials lasting as long as a year found it well tolerated, and it has few known drug interactions. The real concern is rare liver injuryDrug-induced liver injuryLiver damage caused by a medicine, herbal product or supplement. It is usually rare and unpredictable, but it can be serious.More in the glossary: dozens of cases, a few needing a transplant, have been reported in people taking products labelled black cohosh. Whether the herb, a substituted plant or something else was to blame is still debated.

Black cohosh is the root of Actaea racemosa (also called Cimicifuga racemosa), a North American plant of the buttercup family. It has been used medicinally in Germany since the late 19th century, and the European Medicines Agency accepts certain extracts as medicines for hot flushes and sweating.

What dose is normal?

The EU herbal monograph, which sets the dose for licensed medicines, lists three standard dry extracts with daily doses between 5 and 6.5 mg: one taken as 2.8 mg twice a day, one as a single 6.5 mg dose, and an isopropanol extract at 2.5 or 5 mg once or twice a day. These are small amounts of concentrated extract, so milligram figures on US supplements, which may refer to raw root or other extracts, are not directly comparable.

The monograph sets a limit of six months without medical advice and says it has no relevant use in men, children or adolescents.

How serious is the liver risk?

This is the question that decides the score. LiverToxLiverToxA free US National Institutes of Health database that summarises what is known about liver injury caused by medicines, herbs and supplements.More in the glossary, the US National Institutes of Health database on drug-induced liver injuryDrug-induced liver injuryLiver damage caused by a medicine, herbal product or supplement. It is usually rare and unpredictable, but it can be serious.More in the glossary, says products labelled black cohosh have been implicated in many cases of acute liver injury, some severe enough to require an emergency liver transplant or to end in death.

The European review was more cautious. In 2007 its herbal committee examined 44 reported cases, many poorly documented. It found four where liver damage and black cohosh intake fitted together, two of them probable, both a form of autoimmune hepatitis. Four further cases had appeared by 2010. Controlled trials reviewed by the EMA showed no clinically relevant changes in liver tests.

The EMA's response was to require a warning on every licensed product: take it with caution if you have had liver problems, and stop and see a doctor at once if you develop tiredness, loss of appetite, yellow skin or eyes, severe upper stomach pain with nausea, or dark urine. Germany added a dedicated pharmacovigilance plan in 2009.

For comparison, valerian has a cleaner liver record, and some valerian liver cases involved blends that also contained black cohosh.

The wrong-plant problem

Some of the liver cases may come from products that were not black cohosh at all. NCCIH notes that some commercial products contained the wrong herb or unlisted mixtures. In a 2012 DNA study of 36 US black cohosh supplements, 27 matched black cohosh and 9 (25%) matched three Asian Actaea species, which are cheaper and have a different chemistry.

Licensed medicines in the EU and UK use defined extracts that must meet the European Pharmacopoeia standard. In the US, a USP VerifiedThird-party testingTesting of a supplement by an independent lab to check that it contains what the label says and is free of set contaminants.More in the glossary mark is the best available signal of identity testing.

Interactions and hormone questions

Black cohosh does not appear to change how the liver clears most drugs. In a 28-day study in healthy volunteers, it reduced CYP2D6CYP450 enzymesA family of liver enzymes that break down many medicines. When another drug or supplement speeds them up or slows them down, drug levels change.More in the glossary activity by about 7%, a change the authors judged not clinically relevant, and the EU monograph lists no reported interactions. A lab study suggested it might affect how tamoxifen is converted to its active form, which is one reason for caution after breast cancer.

The EMA advises against taking it together with oestrogens unless a doctor recommends it, and says people treated for breast cancer or other hormone-dependent cancers should not use it without medical advice. In an open study of 400 postmenopausal women reviewed by the EMA, it showed no oestrogen-like effect on the womb lining.

Who should be careful

• Anyone with liver disease or a history of liver problems, or who drinks heavily.
• Women on hormone therapy, or who have had breast or womb cancer: talk to your doctor first.
• Pregnant or breastfeeding women: the EMA does not recommend it, and NCCIH says it may not be safe.
• Anyone who notices vaginal bleeding while taking it: see a doctor.

Do not confuse it with blue cohosh, a different plant that can raise blood pressure and has been linked to serious harm in newborns when used to induce labour.

How we scored it

Interactions (80) and dose safety (75) are the strongest factors: trials show it is well tolerated, with few drug effects. Organ toxicity (50) and product quality (50) pull the score down because of rare severe liver cases and frequent substitution with other species. It scores level with turmeric, another herb with rare but serious liver cases, below ginseng, and well above kava.