Four-Agents Decoction ( Si Wu Tang) is composed of dry roots of four plants native to China: prepared Radix Rehmanniae praeparata (Soe Dee Huang), Radix Paeoniae Alba (Bai Sau), Radix Angelicae Sinensis (Dang Guay), and Rhizoma Ligustici Chuanxiong (Tsuan Chyong).

This formula is originally listed in the Prescriptions of People’s Welfare Pharmacy (in Chinese) as a remedy for nourishing the blood and has been used as a basic formula in traditional Chinese medicine for treating women’s illnesses since the Song dynasty (twelfth century). Although many analgesics are available, this formula is worth studying, as non-specified dysmenorrhoea is still one of the most common gynecological complaints in young women worldwide.

New research by scientists in Taiwan has shown that the 800-year-old formula does not significantly reduce menstrual pain after three cycles of treatment; however, a beneficial effect may be present after a longer treatment.

“We did not obtain clear evidence for our hypothesis that Four-Agents-Decoction had a beneficial effect to treat primary dysmenorrhoea” says Dr. Lan Lan Liang Yeh, the study’s principal investigator. “But the unexpected result of a statistically significant pain-reducing effect in the first post-treatment cycle is intriguing and warrants a rigorous similar trial with a larger sample size, a longer treatment phase, and multiple batched study products in different populations to determine the definitive efficacy of this historically documented formula.”

The participants in the study were 78 primary dysmenorrheic women in the Taipei, Taiwan, metropolitan area. At the end of treatment, both menstrual overall–pain- and peak-pain-intensity did not differ significantly between the Four-Agents-Decoction group and the placebo group. But statistically significant pain-reducing effect appeared in the first follow-up cycle.

Source: A Randomised Placebo-Controlled Trial of a Traditional Chinese Herbal Formula in the Treatment of Primary Dysmenorrhoea, Yeh LLL, Liu J, Lin K, Liu Y, Chiou J, et al. (2007), PLoS ONE 2(8): e719. doi:10.1371/journal.pone.0000719