Xiao Yao San is a blend of herbs used for centuries in Traditional Chinese Medicine (TCM). Traditional Chinese medicine practitioners believe that Xiao Yao San works by clearing stagnation in the liver to improve the flow of qi (energy). Stagnant liver qi is said to affect the blood and contribute to stress / mood swings, pain, irritability, constipation, abdominal pain, premenstrual syndrome (PMS), and irregular menstrual periods.
Xiao Yao San can be mixed by hand with the herbs themselves, but it is also sold as a dietary supplement. Although the blends may vary, the herbs that are most frequently combined in Xiao Yao San are:
Chai Hu (Radix Bupleuri)
Bai Zhu (Rhizoma Attraylodis Macrocephalae)
Fu Ling (Poria)
Dang Gui (Radix Angelicae Sinensis)
Bai Shao (Radix Paeoniae Albae)
Sheng Jiang (Rhizoma Zingiberis)
Bo He (Herba Menthae Haplocalycis)
Gan Cao (Radix Glycyrrhizae)
A variation called Jia Wei Xiao Yao San contains all eight herbs with the addition of peony bark and gardenia fruit.
Although there is limited scientific research looking at the effectiveness of Xiao Yao San for therapeutic reasons, and most of what does exist are animal studies, there are a handful of diseases and conditions for which the herbal blend appears promising.
An animal study published in Phytotherapy Research suggests that Xiao Yao San may help alleviate depression by enhancing amino acid metabolism and altering the intestinal microflora.
An evidence-based review published in Complementary and Alternative Medicine included 26 randomized controlled trials involving 1,837 people with depression. The studies compared Xiao Yao San with a placebo and different antidepressants, and also looked at it as an adjunct to antidepressants.
The review concluded that Xiao Yao San appeared to improve the efficacy of antidepressants.
Post-traumatic stress disorder
In 2009, researchers found that Xiao Yao San reduced stress-induced anxiety behaviors in rats. A later study linked this effect to allopregnanolone, a neurosteroid, a natural hormone derived from progesterone identified as a key player in the development of PTSD.
Again, using stress-induced rats, the researchers found that Xiao Yao San not only reduced anxiety behaviors, but also increased brain levels of allopregnanolone.
The anti-inflammatory compounds in Xiao Yao San may be key to its beneficial impact on PTSD, according to a 2017 study. Researchers found that these compounds, previously shown to alleviate depression, impact neurobiological pathways associated with PTSD symptoms. .
Additionally, a 2017 study found that the blend counteracts oxidative stress using pathways similar to those of the antidepressant Prozac (fluoxetine), a common treatment for PTSD.
Research investigating Xiao Yao San's effect on stress is limited to rodent studies. The stress hormone cortisol impacts neurons in the hippocampus, the part of the brain responsible for concentration, memory, and mood. A study in rats found that Xiao Yao San appears to protect against this.
Xiao Yao San is traditionally used to soothe a "sour" stomach. Current research suggests that the herbal blend helps relieve functional dyspepsia, better known as chronic indigestion.
According to a review of 14 studies published in the Journal of Gastroenterology and Hepatology, Xiao Yao San can help relieve stomach discomfort, nausea, bloating, and belching associated with indigestion.
The researchers noted that the herbal preparation appears to work just as well as prokinetic drugs, drugs that increase intestinal motility, such as Motilium (domperidone) and Reglan (metoclopramide).
A 2018 review of Chinese herbal remedies for indigestion also confirmed these results and suggested that Xiao Yao San was more effective than prokinetic drugs.
Formulas based on the Xiao Yao San formula: