Side effects are uncommon, but occasional stomach pains and intestinal discomfort, dizziness, nausea, severe headaches, stiffness, and trembling limbs have been noted. Germany’s Commission E, which is similar to the US Food and Drug Administration, recommends that black cohosh not be used for more than 6 months, since no studies have been conducted for longer periods.
Black cohosh has weak estrogenic effect on the breast and should be used cautiously in patients with breast cancer or a high risk of breast cancer. A 2-month double-blind, randomized controlled trial of black cohosh in breast cancer survivors demonstrated no short-term side effects; however, therapy was only significantly beneficial in relieving sweating and ineffective in reducing flushes.24 The long-term effects are unknown. A recent systematic review suggests that the side effects of black cohosh are transient, and severe adverse event reports are unproven (Table 2).24
Dong quai
Dong quai, a common Chinese herb extracted from the Angelica sinensis root, has become popular in the US. In contrast to China, where it is sold as part of a mixture that includes several other herbs, dong quai typically is sold in the US as a single herb.
Although some women report improvements in their vasomotor symptoms, there have been very few studies on the effects of dong quai on menopause. In one 24-week study of 71 postmenopausal women, researchers could not demonstrate a significant difference between dong quai and placebo in alleviating vasomotor symptoms (LOE: 2b).25 The investigators suggested that studying the effects of dong quai alone, rather than in combination with other herbs, may have been a factor in their findings.
Two caveats: Dong quai increases photosensitivity, so women taking the herb should be cautioned that too much exposure to sunlight may result in a rash. Also it has been reported to potentiate the effects of warfarin (Table 2). It should not be used during pregnancy.26
Evening primrose
Native Americans consumed the leaves, roots, and seedpods of evening primrose (Oenothera biennis) for food, and made extracts from it to treat a variety of conditions. Today, the flowers and seeds are pressed to make oil that is high in the omega-6 fatty acid gamma-linolenic acid (known as GLA) and essential polyunsaturated fatty acids, which convert into prostaglandins. Evening primrose oil also is a good source of linoleic acid.
Although there are a number of good studies in which evening primrose oil has been used to successfully treat eczema and several other conditions with few side effects, it appears to have no benefit over placebo for hot flushes (LOE: 2b).27
Patients should be warned that mild upset stomach, indigestion, nausea, softening of stools, and mild headaches may occasionally occur. Also, evening primrose is contraindicated in women taking seizure medications or antipsychotics because it lowers the seizure threshold in patients on phenothiazines (Table 2).
Red clover
Red clover (Trifolium pratense) is a plant that contains the phytoestrogens formononetin, biochanin A, daidzein, and genistein. It was originally used by Native Americans to treat whooping cough, gout, and cancer.
Two clinical trials conducted in Australia failed to demonstrate that red clover extract was more effective than placebo in reducing vasomotor symptoms (LOE: 2b).28,29 However, one recent presentation found that women who took 40 mg of red clover per day—the recommended dosage—experienced a significant reduction in hot flushes.30
There is still little information on whether red clover will have any effect on the uterine lining or breast tissue. Because red clover contains coumarin-like substances, high dosages may cause the blood to thin (Table 2).31