The oral LD50 for rats is 17,000 to 27,211 mg/kg.MSDS

Clinical trials using a variety of black cohosh formulas to manage menopausal symptoms have shown that its use is associated with a low incidence of adverse effects. The most commonly reported side effects are gastrointestinal discomfort and rashes, both of which have shown to be mild and transient. Some other adverse effects in clinical trials have included breast pain or enlargement, infection, vaginal bleeding or spotting, and musculoskeletal discomfort. The incidence of these symptoms, however, was similar in women taking black cohosh and those taking a placebo.^L2303

Reports have been made globally of at least 83 cases of liver damage—including hepatitis, liver failure, elevated liver enzymes, and various other liver injuries—associated with black cohosh use. However, no evidence of a causal relationship exists. It is possible that a subset of reported cases of hepatotoxicity were due to impurities, adulterants, or incorrect Acteae species in the black cohosh products used. However, no independent analysis of these drugs has been done to confirm the existence of these problems.^L2303

The American Herbal Products Association recommends that pregnant women not ingest black cohosh, except under the supervision of their healthcare provider because studies have not thoroughly evaluated its use during pregnancy. The U.S. Pharmacopeia advises that individuals with liver disorders should also avoid the use of black cohosh. In addition, users who develop symptoms of liver disease, such as abdominal pain, dark urine, or jaundice, while taking the supplement should discontinue use and contact their healthcare provider.^L2303

As with other drugs believed to have potential estrogenic effects, there has been concern about the safety of black cohosh in women with a personal history or family history of breast cancer. Though further research is warranted, at least one tissue-culture study showed no stimulation of estrogen receptor-positive breast cancer cell lines by black cohosh extract.^A32559 This study found that black cohosh extract amplified the inhibitory action of tamoxifen (Nolvadex) on breast cancer cell lines. Because this question has not yet been fully answered, physicians should discuss this issue with their patients who are at risk of breast cancer while considering taking black cohosh.^L2307

Black cohosh is contraindicated during pregnancy due to its potential ability to promote uterine contraction. The safety of black cohosh in breastfeeding mothers and the level of transmission of black cohosh in breast milk are both unknown.^L2307