• Basic Info
• Top Questions

Interactions

Interactions with Drugs

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 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 alter the way the liver breaks down or metabolizes certain drugs. In theory, due to possible alcohol content in some tinctures of black cohosh, combination with disulfiram (Antabuse®) or metronidazole (Flagyl®) may cause nausea and vomiting.

Although not well studied in humans, black cohosh may potentially interact with antidepressants, antihistamines, and antioxidants. It may also interact with agents taken for the treatment of cancer and osteoporosis.

Interactions with Herbs and Dietary Supplements

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 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 multi-organ 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 lower blood pressure and therefore interact with other herbs or supplements that also affect blood pressure.

In theory, 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, fewer cases with garlic, and two cases with saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.

Black cohosh may alter the way the liver breaks down or metabolizes certain herbs and supplements.

Although not well studied in humans, black cohosh may potentially interact with herbs and supplements with antidepressant, antihistamine, or antioxidant effects. It may also interact with herbs or supplements taken for the treatment of cancer and osteoporosis