Black cohosh is a member of the buttercup plant family native to North America and is not to be confused with blue cohosh or white cohosh, which are unrelated. Black cohosh was used by Native Americans for variety of diseases and by 9th century Americans for rheumatism and fever. Today, it's taken primarily for hot flashes and other menopausal symptoms, but those same estrogenic properties may cause serious side effects in some people.
Blood Clots, Blood Vessels
An article in a 2005 issue of the "Postgraduate Medical Journal" reported that a patient with protein S deficiency, which causes an increased risk of blood clots, did indeed develop clots after taking black cohosh with other herbal products. Although it's not known if black cohosh alone was the cause, if you have protein S deficiency, you should probably avoid the herb. Black cohosh may also be associated with cutaneous vasculitis, an inflammation of blood vessels, according to the Sloan-Kettering Institute.
Drug Interactions
Black cohosh taken together with Tamoxifen and other chemotherapy drugs may increase the toxicity of those drugs. The National Institutes of Health also warn that black cohosh may decrease the effectiveness of cisplatin in cancer treatments. Black cohosh could also interact with drugs metabolized by the CYP3A4 enzyme or any drugs that are changed and broken down by the liver. These include everything from Elavil to Prozac, so if you're on any prescription medication, check with your doctor before taking black cohosh.
Estrogenic Effects
The National Institutes of Health reported that a large study following women on estrogen medications showed a small but significant increase in the risk of certain diseases. Due to the uncertainty about how potent the estrogenic qualities of black cohosh are, especially over long periods, you should avoid taking black cohosh if you have breast cancer or another hormone-related disease such as uterine or ovarian cancer, endometriosis or fibroids, or are in a high risk group for these diseases.
Kidney Damage
A 2003 report in the "American Journal of Transplantation" linked a patient who had received a kidney transplant to transplant rejection because the patient took a product containing black cohosh plus alfalfa. If you're a kidney transplant recipient, it may be wise to avoid black cohosh supplements.
Liver Damage
One of the most serious side effect concerns surrounding black cohosh is possible liver damage. One woman taking black cohosh for symptoms of menopause developed an acute case of hepatitis, which required a liver transplant three weeks after she started taking the herb.
Liver disease has also been reported in other people taking the herb, which has prompted the U.S. Pharmcopeia, the standards-setting organization for food and drugs, to advise that black cohosh be labeled with a cautionary statement. If you take black cohosh and develop signs of liver trouble such as abdominal pain, dark urine or jaundice, discontinue use and contact your physician.
Pregnancy and Delivery
Black cohosh has uterine-stimulating effects and may cause premature birth in large doses. There are also published reports about babies of mothers taking black cohosh developing neurological problems. Women who are nursing should also avoid the herb, as it may cause colic in infants.
Other Side Effects
The most-common side effects from taking black cohosh are stomach upset and rashes. In large doses of 5 to 12 grams, black cohosh can cause headaches, dizziness, tremors, low blood pressure, low pulse rate, vomiting, heaviness in the legs and vision problems. One case of seizures has also been reported.
Standardization
Researchers at Columbia University, the City University of New York and the Chinese Academy of Sciences analyzed the chemical components of 11 different black cohosh products in the U.S. They found that four of them contained an Asian species of black cohosh, which has different chemical properties. They concluded that the varying makeup of such products may produce different and unexpected health effects, and thus, consumers should use caution.
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