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Higher doses are recommended for black cohosh consumed as tea because it is less easily absorbed by the body.

The FDA do not regulate black cohosh, so the purity, quality, and strength of different supplements and brands vary. Recommended doses depend on the specific product, and there is no recognized standard dose. People should be sure to buy any products from a reputable source.

Black cohosh preparations are usually made from the root and underground stems of the herb. These are most commonly consumed as a ground powder, liquid mixture, or as extract in a pill.

General dosing information for black cohosh root is drawn mostly from traditional or theoretical data.

Authoritative and recent resources vary. The British Herbal Compendium recommends taking 40-200 milligrams (mg) of the herb in dried form, spread throughout the day into individual doses. Traditionally, much higher doses spread out evenly in three doses were recommended.

In liquid or tincture form, doses of 0.4-2 milliliters of a 60 percent ethanol mixture may be enough. For less easily absorbed forms of the herb, such as teas or powders, 1-2 gram (g) doses are recommended three times daily.

Other studies have shown benefits from taking 6.5 to 160 mg of black cohosh orally for up to a year. In liquid or tincture form, some studies showed menopause symptom relief with 40 drops of the herb mixture taken orally one or twice daily for up to 24 weeks.

Limited studies have shown that certain doses of black cohosh may be more effective than others at treating individual menopause symptoms.

Additional potential dosing recommendations include:

  • Postmenopausal breast cancer: One to four 2.5 mg tablets daily for 6 months alongside tamoxifen, or 20 mg daily taken orally for one year.
  • Postmenopausal heart disease: 40 mg daily for 3 months, stopped, then taken for another 3 months.
  • Mental performance in postmenopausal women: 128 mg daily for 1 year.
  • Bone density in postmenopausal women: 40 mg daily for as many as 3 months.

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People with pre-existing conditions may have a higher risk of experiencing adverse side effects.

There is little to no long-term data on the risks associated with black cohosh use.

As black cohosh preparations are not regulated by the FDA, there is also a chance that products may contain other botanical or chemical ingredients that could cause harm.

Because of these uncertainties, the North American Menopause Society do not recommend the use of the herb for the treatment of menopause symptoms. Most health authorities and studies suggest that if black cohosh is used, it should only be taken for a maximum of one year.

Though rare, liver injury is the most studied, and potentially the most dangerous, complication associated with black cohosh use. Those with signs of jaundice or liver failure should immediately see a doctor. If the signs are severe, they should seek emergency care.

Common signs of jaundice include:

  • yellowing of the skin and eyes
  • severe upper stomach pain or cramps
  • nausea and vomiting
  • extreme tiredness not related to exercise or lack of sleep
  • dark urine

Many additional health complications of varying severity have been connected with the use of the black cohosh.

As the herb acts as a blood thinner, bleeding and blood pressure disturbances may occur with use. A doctor should assess symptoms that involve bleeding or become severe.

The full list of currently known side effects of black cohosh use includes:

  • abnormal or increased vaginal discharge
  • vaginal bleeding or stimulation of menstrual flow
  • abnormal heartbeat or altered blood pressure, typically lowered
  • blood clots, especially in the legs
  • breast cancer recurrence
  • fluid buildup
  • headache
  • irritability, moodiness, depression
  • breast pain or tenderness
  • chest discomfort
  • constipation
  • liver damage or failure
  • hepatitis infection
  • muscle weakness
  • minor skin irritations or lesions
  • eye inflammation
  • nausea and vomiting
  • dizziness or vertigo
  • overgrowth of the uterine lining
  • seizures
  • excessive sweating
  • general swelling
  • fatigue
  • mild visual impairments
  • weight gain

Certain people may be at a higher risk of complications if using black cohosh. Those on estrogen or hormone therapies may not be able to take it safely.

Factors that increase the likelihood of adverse reactions to black cohosh include:

  • hormone-sensitive conditions, such as breast and uterine cancers, and endometriosis
  • seizure disorders
  • liver disease
  • history of stroke
  • conditions involving blood clots
  • medication that lowers blood pressure
  • estrogen medications and hormone replacement therapies
  • blood-thinning and antiplatelet medications
  • nonsteroidal anti-inflammatory medications
  • alcohol use

In many classes of medications, there are ones that increase the risk of complications and interaction when used alongside black cohosh. These classes include:

  • liver medications
  • osteoporosis and arthritis medications
  • depression and mood medications
  • anti-seizure medications
  • antihistamines
  • cancer medications
  • cholesterol medications

Some people are allergic to black cohosh and its components. The herb may also contain small levels of salicylic acid, the active component in aspirin. People with aspirin intolerance or allergies should avoid it.

Black cohosh may also interact negatively with other herbs or traditional remedies. Supplements used to treat conditions, such as those considered risk factors for black cohosh use, might also raise the chance of side effects when used alongside this herb.

Natural supplements to avoid while using black cohosh include:

  • chaste-tree berries
  • evening primrose oil
  • blue cohosh
  • pennyroyal
  • ginkgo biloba
  • garlic
  • saw palmetto
  • willow bark
  • St. John's wart