The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Avoid if allergic to black cohosh or other members of the Ranunculaceae (buttercup or crowfoot) family. In nature, black cohosh contains small amounts of salicylic acid (which is found in aspirin), but it is not clear how much (if any) is present in commercially available products. Black cohosh should be used cautiously in people allergic to aspirin or to other salicylates.
Side Effects and Warnings
Black cohosh is generally well tolerated in recommended doses and has been studied for up to six months. High doses of black cohosh may cause frontal headache, dizziness, perspiration, or visual disturbances. Several side effects have been noted in studies including constipation, intestinal discomfort, loss of bone mass (leading to osteoporosis), irregular or slow heartbeat, low blood pressure, muscle damage, nausea, and vomiting. Dysphoria and "heaviness in the legs" may occur.
It is not clear if black cohosh is safe in individuals with hormone-sensitive conditions such as breast cancer, uterine cancer, or endometriosis. There is controversy as to whether black cohosh is similar to estrogen in its mechanism, although recent studies suggest that it may not be. The influence of black cohosh on anti-estrogen drugs (like tamoxifen) or hormone replacement therapy is not clear. It is not known if black cohosh possesses the beneficial effects that estrogen is believed to have on bone mass or the potential harmful effects such as increased risk of stroke or hormone-sensitive cancers.
A few gynecologic organ-related adverse events have been reported including vaginal bleeding and miscarriage; however, the effects of black cohosh in these events are unclear.
Hepatitis (liver damage) and liver failure has been reported with the use of black cohosh containing products. Liver transplantation has been required in some patients. These reports are concerning, although the cases have been criticized by some as not being adequately substantiated. Nonetheless, patients with liver disease should consult a licensed healthcare professional before using black cohosh.
Black cohosh should also be used cautiously in patients with a history of blood clots, seizure disorder, or high blood pressure.
Pregnancy and Breastfeeding
Safety during pregnancy and breastfeeding has not been established. Black cohosh may relax the muscular wall of the uterus and some nurse-midwives in the United States use black cohosh to stimulate labor. Black cohosh may also have hormonal effects and caution is advised during breastfeeding. There is one report of severe multi-organ damage in a child delivered with the aid of both black cohosh and blue cohosh ( Caulophyllum thalictroides ) who was not breathing at the time of birth. The child survived with permanent brain damage. However, blue cohosh is known to have effects on the heart and blood vessels and may have been responsible for these effects.
Tinctures may be ill-advised during pregnancy due to potentially high alcohol content.