Interactions with Drugs
Because black cohosh may contain estrogen-like chemicals, the effects of other agents believed to have estrogen-like properties may be altered. The potential estrogen-like effects of black cohosh remain debated, and the active chemical contents of black cohosh have not been clearly identified. Although recent studies suggest no significant effects of black cohosh on estrogen receptors in the body, caution is warranted in people taking both black cohosh and estrogens, due to unknown effects. The influence of black cohosh in combination with tamoxifen is not clear in studies, and it is not known if tamoxifen counteracts the effects of black cohosh. Drugs like raloxifene may also interact.
Black cohosh may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants (blood thinners) such as warfarin (Coumadin®) or heparin, antiplatelet drugs such as clopidogrel (Plavix®), and nonsteroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).
Black cohosh may lower blood pressure and therefore should be used cautiously with other hypotensive agents such as beta-blockers like metoprolol (Lopressor®, Toprol®) or propranolol (Inderal®) and calcium-channel blockers like diltiazem (Cardizem®, Tiazac®) or verapamil (Isoptin®, Calan®). Black cohosh may contain small amounts of salicylic acid and may increase the anti-platelet effects of other agents such as aspirin.
Black cohosh may interfere with the way the body processes certain drugs using the liver's cytochrome P450 enzyme system. As a result, the levels of these drugs may be altered in the blood and change the intended effects. People taking any medications should check the package insert and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.
Black cohosh may also interact with agents for arthritis, cancer, or osteoporosis; agents for depression or selective serotonin reuptake inhibitors (SSRIs); agents for inflammation, pain relief, or sensation loss; agents for the brain, intestines, or stomach; agents taken by mouth; agents that affect dopamine; agents that inhibit blood clots and platelet aggregation; agents that may lower seizure threshold; agents that widen blood vessels; agents toxic to the liver; alcohol; antihistamines; cholesterol-lowering agents; estrogens; hormonal agents; raloxifene; salicylate-containing agents (e.g., aspirin); and tamoxifen.
Many tinctures contain high levels of alcohol and may cause nausea or vomiting when taken with metronidazole (Flagyl®) or disulfiram (Antabuse®).
Interactions with Herbs and Dietary Supplements
Because black cohosh contains estrogen-like chemicals, the effects of other agents believed to have estrogen-like properties may be altered. Black cohosh should be used cautiously in people taking herbs with possible hormonal effects. This is a theoretical concern, and it is not clear if the amounts of salicylates present in commercial or processed black cohosh products have significant effects in humans.
Seizures were reported in a woman taking a combination of black cohosh, chaste-tree (berries and seeds), and evening primrose oil for four months and who also consumed alcohol. The cause of her seizures is not clear.
Both black cohosh and blue cohosh (Caulophyllum thalictroides) are used by nurse-midwives in the United States to assist birth. There is one report of severe multiorgan damage in a child delivered with the aid of both black cohosh and blue cohosh 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. Pennyroyal and black cohosh should not be used together, as there is a possibility of increased toxicity and death.
Black cohosh may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.
Black cohosh may lower blood pressure and therefore interact with other herbs or supplements that also affect blood pressure.
Black cohosh may interfere with the way the body processes certain herbs or supplements using the liver's cytochrome P450 enzyme system. As a result, the levels of other herbs or supplements may become changed in the blood. It may also alter the effects that other herbs or supplements possibly have on the P450 system.
Black cohosh may potentially interact with American pennyroyal; antihistamines; antioxidants; blue cohosh (Caulophyllum thalictroides); chasteberry; cholesterol lowering herbs and supplements; evening primrose oil; herbs and supplements for arthritis, cancer, or osteoporosis; herbs and supplements for depression or selective serotonin reuptake inhibitors (SSRIs); herbs and supplements for inflammation, pain relief or sensation loss; herbs and supplements for the brain, intestines or stomach; herbs and supplements taken by mouth; herbs and supplements that alter the effect of dopamine; herbs and supplements that inhibit blood clots and platelet aggregation; herbs and supplements that may lower seizure threshold; herbs and supplements that prevent androgen expression; herbs and supplements that widen blood vessels; herbs and supplements toxic to the liver; hormonal herbs and supplements; hormone replacement therapy herbs and supplements; salicylate-containing herbs and supplements (e.g., willowbark); and St. John's wort.
This evidence-based monograph was prepared by The Natural Standard Research Collaboration