Similar results were seen in open studies. Based on these and other results, black cohosh came to be described as a phytoestrogen a plant that produces effects similar to estrogen. An animal study has also found no evidence that black cohosh works like estrogen. The answer is that we really don t know. The standard dosage of black cohosh is 1 to 2 tablets twice daily of a standardized extract manufactured to contain 1 mg of 27-deoxyacteine per tablet.
Blue cohosh is potentially more dangerous because it contains chemicals that are toxic to the heart.
A recent case report indicates that it caused severe heart problems in a woman who took blue cohosh during pregnancy. 6 Safety Issues Black cohosh seldom produces any obvious side effects, other than occasional mild gastrointestinal distress. Studies in rats have shown no significant toxicity when black cohosh was given at 90 times the therapeutic dosage for a period of 6 months. Because 6 months in a rat corresponds to decades in a human, this study appears to make a strong statement about the long-term safety of black cohosh. Unlike estrogen, black cohosh does not stimulate breast cancer cells growing in a test tube.