The popular herbal remedy St. John’s wort may help ease menopausal hot flashes, a small study suggests.

St. John’s wort is probably best known as an herbal antidepressant, with some clinical trials suggesting that it can help relieve mild to moderate depression symptoms.

A few studies have also investigated the herb’s effects on menopausal symptoms, but have focused on its impact on mood - and not the so-called vasomotor symptoms of menopause, which include hot flashes and night sweats.

“(The) findings of our study suggest that this herbal medicine can be used to treat hot flashes due to menopause, and it is a new finding about the usage of St. John’s wort,” Marjan Khajehei, of Shiraz University of Medical Sciences in Iran, told Reuters Health in an email.

Khajehei and her colleagues found that among a group of women they randomly assigned to take either St. John’s wort or an inactive placebo for eight weeks, those using the herb saw a greater reduction in daily hot flashes.

Among women taking St. John’s wort, the average number of hot flashes declined from roughly four per day at the start of the study to fewer than two per day at week eight. In contrast, women in the placebo group were having an average of 2.6 hot flashes per day by the eighth week.

The herb also appeared to lessen the duration and severity of the women’s hot flashes, Khajehei and her colleagues report in the journal Menopause.

The study included 100 women who were 50 years old, on average, and had been having moderate to severe hot flashes at least once per day. The women were randomly assigned to take either drops containing St. John’s wort extract or placebo drops three times a day for eight weeks.

While women in both groups saw their hot flashes improve, those taking the herbal extract had a better response, on average.

St. John’s wort contains estrogen-like plant compounds called phytoestrogens, and it’s possible that these compounds explain the benefits seen in this study, according to Khajehei.

However, she said, further research is needed to confirm that the herb eases hot flashes and that phytoestrogens are the reason.

St. John’s wort is generally considered safe when taken as directed, Khajehei noted. Still, she added, since phytoestrogens have mild estrogen-like effects in the body, women who have any contraindications to using estrogen - such as a history of breast or endometrial cancers - should talk with their doctors before starting St. John’s wort.

The herb has also been shown to interact with certain medications, including antidepressants, the heart medication digoxin and the blood thinner warfarin. Experts generally recommend that people on any medication talk with their doctors before starting an herbal remedy.

SOURCE: Menopause, February 2010.