Black Cohosh

What side effects can black cohosh cause?

Black cohosh was generally well tolerated in studies lasting up to a year. The EU monograph lists allergic skin reactions, swelling of the face and limbs, and digestive complaints such as indigestion and diarrhea, with unknown frequency. 1 2

In pooled trials, dropout rates with black cohosh were similar to placebo. 3

Can black cohosh harm the liver?

Cases of liver damage, some very serious, have been reported in people taking products labeled as black cohosh. NCCIH calls them rare and notes that it is uncertain whether black cohosh caused them. 1

A US Pharmacopeia committee reviewed 30 case reports and rated all as possibly, not probably, related. It still decided that products should carry a cautionary statement. 4

A meta-analysis of five controlled trials with 1,117 women taking an isopropanolic extract for 3 to 6 months found no effect on liver enzymes. That analysis was led by staff of the extract's manufacturer. 5

The EU monograph lists liver toxicity as a known adverse effect. People should stop and see a doctor if they develop tiredness, loss of appetite, yellow skin or eyes, severe upper stomach pain with nausea, or dark urine. People with a history of liver disorders should use it with caution, and EU regulators keep monitoring the risk. 2 6

Is black cohosh safe after breast cancer?

Observational studies found no link between black cohosh use and breast cancer, and a large retrospective cohort of breast cancer patients found no higher recurrence rate among users of an isopropanolic extract. 7

In tumor-bearing mice, an extract increased the share of animals with lung metastases. The EU monograph says an influence on hormone-dependent tumors cannot be excluded and that patients treated for breast cancer should not use it without medical advice. NCCIH also calls its safety uncertain after hormone-sensitive cancers. 1 2

A US two-year study gave rats and mice very high doses by gavage and found equivocal evidence of uterine tumors in female rats. The EU committee judged the human relevance unknown, given doses far above those used in people. 6

Interactions with medicines

The EU monograph reports no known interactions but advises against combining black cohosh with estrogens unless a doctor recommends it. 2

In healthy volunteers, black cohosh weakly inhibited the liver enzyme CYP2D6, by about 7%, which the authors did not consider clinically relevant, and it did not affect CYP3A4, CYP1A2 or CYP2E1. Because tamoxifen is mainly processed by CYP2D6, NCI notes that even mild inhibition may deserve attention. 7 8

Memorial Sloan Kettering lists laboratory and case findings on tamoxifen, some chemotherapy drugs and simvastatin, and reports that liver problems were most often seen when black cohosh was combined with prescription drugs. NCCIH advises people on any medicine to talk with their provider first. 1 9

Who should be careful?

Pregnancy and breastfeeding: safety has not been established and use is not recommended. Memorial Sloan Kettering advises pregnant women to avoid it because of a possible abortifacient effect. 1 2 9

People with liver disease, people treated for breast cancer or other hormone-dependent tumors, and anyone using estrogens should take medical advice first. If vaginal bleeding or other new symptoms occur, a doctor should be consulted. 2

Doses studied and how long

Trials used a median of 40 mg per day of root equivalent. EU-licensed products give 5 to 6.5 mg dry extract per day, depending on the extract. 2 10

Because long-term safety data are lacking, the EU monograph says black cohosh should not be taken for more than 6 months without medical advice. There is no official upper limit. 2 7