The majority of the trials used a combination of more than five herbs. The most common herbs were Chinese angelica root (Danggui), Szechuan lovage root (Chuanxiong), red peony root (Chishao), and white peony root (Baishao).
Just how the herbs might help isn't exactly understood. According to traditional Chinese medicine, these herbs can regulate the flow of energy (called "qi") and blood, warm the body, and improve the flow of energy through the liver and kidney. In scientific terms, the researchers said that the herbs could affect hormone levels and blood circulation.
The Australian-based study involved 3,475 women in China, Taiwan, Japan and the Netherlands. More studies are needed, however, because many of the ones included in the review had a small number of participants or could have been better-designed.