Black and blue cohosh are two unrelated herbs commonly used for women's health issues. Both of these herbs have a long traditional use as a uterine stimulant, both for the induction of labor and to trigger abortion. Midwives and herbalists may recommend these herbs late in the third trimester to help prepare the body for birth or encourage labor to begin; however, they should only be used under close professional supervision.
Blue cohosh, or Caulophyllum thalictroides, has several pregnancy related uses. It is a uterine tonic and toner and may be taken the last few weeks of pregnancy to prepare the uterus for birth and in higher doses to induce labor. According to a study in the Canadian Journal of Clinical Pharmacology, 64% of midwives in the United States have used blue cohosh as a labor inducer. Taken early in pregnancy, the uterine contractions caused by blue cohosh may trigger a miscarriage.
Black cohosh, or Cimicifuga racemosa, is said to help to ripen and open the cervix late in pregnancy. According to WebMD, approximately 45% of midwives in the United States use black cohosh as a labor aid; however, there are no studies confirming the efficacy of this. Used earlier in pregnancy, black cohosh may put the pregnancy at risk and has been used along with other herbs to intentionally trigger miscarriage.
Herbal preparations intended to induce labor or prepare the cervix and uterus for birth should only be taken in the last few weeks of pregnancy. Taking blue cohosh or black cohosh earlier in pregnancy could result in a pre-term baby or other significant complications. While these herbs have a long traditional use, recent information suggests that blue cohosh in particular poses significant dangers to the fetus.
Blue cohosh may have historically been used a uterine stimulant, but that does not make it a safe choice for labor inductions. Aviva Jill Romm, a prominent herbalist, states that blue cohosh has teratogenic properties and that these properties may be responsible for several negative outcomes associated with blue cohosh, including an infant with heart failure. A study on the safety of blue cohosh published in the Canadian Journal of Clinical Pharmacology recommends that blue cohosh preparations be removed from the market.
Both blue and black cohosh pose risks of potential side effects. Blue cohosh may affect blood pressure, causing an unsafe increase in blood pressure for the laboring mother. Black cohosh seems to cause fewer side effects, but there are some reports of liver problems, including liver failure with regular use, according to the National Institutes of Health. Digestive side effects may also accompany black cohosh.