Black Cohosh Side Effects


While the list of black cohosh benefits appears to be growing everyday,  there are some things you may want to keep an eye on.  While there is not a whole lot of information available on the subject,  and some results seem to contradict one another,  I urge you to read this carefully and then make your own decision.

Toxic Effects

In human studies using a fluid extract of 890 mg a day, no toxic effects were found. In vitro tests showed no mutagenic potential when exposed to black cohosh extract.


Certain estrogens (estradiol) have been associated with increased risk of ovarian, breast, and cervical cancers. Other forms of estrogen (estriol) have been associated with lower rates of cancer. The effect of Remifemin (a proprietary black cohosh extract) have been said by the manufacturer to have estriol like properties, and the German Commission E has not issued and warnings about taking black cohosh in patients with estrogen dependent tumors.

It would be wise to consult your doctor if you have estrogen dependent tumor activity; however, in vitro studies have shown an anti-proliferation effect on tumor cells from black cohosh extract. In a study of 50 day old female rats with estrogen dependent tumors, doses of black cohosh extract equivalent to 100 times the average therapeutic dose for humans failed to show any tumor promoting activity. Another study done in China seems to have shown completely opposite results; however, the reasons for this are not clear.

Drug Interactions

Standardized black cohosh extracts have been studied with hormone replacement therapy with minimal side effects. A combination of Black cohosh extract and St. Johns wort showed minimal side effects. In a study involving 800 women, 99% tolerated this combination very well.

One case of seizures was reported in a 45 year old woman while combining black cohosh extract with Vitex angus-castus and evening primrose oil; however, with the amount of unknowns in this case, it is impossible to say if the supplements were the cause.  In order to avoid possible black cohosh side effects,  please follow the instructions from the manufacturer.

Pregnancy and Lactation

There is little information available on the safety of black cohosh to pregnant women and nursing babies. The American Herbal Products Association’s Botanical Safety Handbook (1997) lists black cohosh extract as a class 2b herbal medicine, meaning that it should not be taken by pregnant women without first consulting a doctor that specializes in herbal medicines.

The American Materia Medica reported in 1919 that high doses of black cohosh given prenatally could help induce labor and prevent hemorrhage. Herbalists have long recommended a dose of black cohosh extract, and blue cohosh to aid with labor. There has been one documented case of a woman who was taking black and blue cohosh when the baby she was carrying was born with no spontaneous breathing; however, there is no direct cause and effect evidence available, and the death was likely due to poor resuscitation practices.

Black Cohosh Side Effects

Jean Brunton reported in 1992 that daily doses of 890 mg of black cohosh appeared to be safe. Minor gastrointestinal discomfort is the only known side effect.  One important thing though is to use the proper black cohosh dosage.  The dosage used in the studies have varied,  so be sure to follow the instructions on the bottle.

The German Commission E recommends daily doses of black cohosh should not exceed 6 months; however, no evidence has been found to suggest that a longer duration would be harmful. Remember to consult a licensed professional if you are pregnant, or plan on taking black cohosh extract for long durations.