Herb Research: Shao Yao Gan Cao Tang

At Root and Branch Medicinary, we are often asked whether there is biomedical evidence that supports the clinical effects we routinely see when using formulas like this one. From a Chinese medicine standpoint, the formula works—its indications are clear, its mechanisms are described in terms of pattern differentiation, and its efficacy is confirmed through centuries of lineage-based clinical observation and our direct, daily experience in our own clinic. Still, we recognize that many people find value in looking at formulas through a modern research lens as well. If you're looking for that kind of evidence though, the research is thin and the papers usually cover small number of participants or are limited to animal tests in mice or rabbits. Nonetheless, we decided to dig around and find some research to offer an additional layer of perspective to the question of what it means for something to "work." In that spirit, we looked into the biomedical research on Sháo Yào Gān Cǎo Tāng that came across our desk to see what current research has to say.

Sháo Yào Gān Cǎo Tāng (芍藥甘草湯), often translated as Peony and Licorice Decoction, is a classical formula with elegant internal logic rooted in the traditional Chinese understanding of flavor and function. The formula consists only of Bái Shāo (白芍, Paeonia lactiflora) and Gān Cǎo (甘草, Glycyrrhiza uralensis), typically in a 2:1 ratio. This pairing combines the sour flavor of Bái Shāo, which nourishes the blood and softens the Liver, with the sweet flavor of Gān Cǎo, which harmonizes and relaxes tension. In classical theory, sour gathers and constrains, while sweet moderates urgency and soothes spasms. When Bái Shāo is used at lower doses, the sour flavor predominates, encouraging a constraining action on the sinews. As the dosage increases, its flavor profile deepens—moving toward bitterness—and it begins to exert a more downward-directing, softening influence. This change in flavor dynamics is mirrored by a change in physiological action. The sweet and sour pairing, especially when Bái Shāo is used in higher proportion, is said to 'relax the sinews and stop pain.' This flavor-based strategy forms the foundation of the formula’s function and helps explain why it has been used consistently across dynasties for pain and cramping conditions.

Traditionally, Sháo Yào Gān Cǎo Tāng is indicated for spasmodic pain due to disharmony between the Liver and Spleen. It is especially useful for cramping of the calves or abdominal musculature, including postpartum cramping or pain following miscarriage. In classical usage, it is often associated with deficiency of yīn or blood, combined with internal wind or constrained qì that leads to pain. The combination of Bái Shāo, which nourishes the blood and relaxes the sinews, with Gān Cǎo, which moderates spasm and tonifies the middle, creates a synergistic effect that has proven both gentle and powerful.

"Yes, but how does it work?" people ask us. On my own, I'd repeat what I just wrote but if they are looking for a biochemical action, one study we found examined the pharmacological activity of the formula’s main constituents and found that paeoniflorin, a compound in Bái Shāo, exhibits calcium channel-blocking effects that may contribute to muscle relaxation[1]. The study was done on rabbits of course and it is essentially just a guess about why the formula may have had a relaxing effect on musculature. But this finding might begin to explain from a biomedical standpoint why the formula is effective for various forms of spasm and tension. While modern research on whole-formula clinical use remains limited, the pharmacological evidence supports the classical rationale for pairing these herbs, particularly in cases involving muscle or sinew tension.

At Root and Branch Medicinary, we source high-quality granule extracts of Sháo Yào Gān Cǎo Tāng from trusted suppliers, ensuring both the purity of individual herbs and the fidelity of the compound formula. Each batch is tested for identity, potency, and contaminants. Additionally, we stock well-sourced and high-quality Bái Shāo and Gān Cǎo in whole plant, bulk form for use in decoction or as a sǎn powder. For clinicians, this provides assurance that when you reach for this simple two-herb formula, you are accessing a preparation that aligns with both classical principles and modern safety standards.

We encourage practitioners to consider Sháo Yào Gān Cǎo Tāng not only for its classical indications, but also for modern contexts in which gentle spasm relief is needed—particularly in patients with complex comorbidities or those who may be sensitive to pharmaceuticals. As with all formulas, careful pattern differentiation remains the cornerstone of safe and effective use, but the pharmacological research on its compounds invites continued confidence in its relevance and clinical value.

If you would like to review published studies or testing certificates for our current batches, we are happy to share them. As always, our goal is to support your clinical work with herbal medicine that is rooted in history, informed by science when helpful, and ready to use in your practice.

[1] Wang F, Yang Y, Ji X, Tao X, Wang Y, Wang C. Effects of Paeoniflorin on the activity of muscle strips, intracellular calcium ion concentration and L‑type voltage‑sensitive calcium ion channels in the sphincter of Oddi of hypercholesterolemic rabbits. Mol Med Rep. 2019 Jun;19(6):5185-5194. doi: 10.3892/mmr.2019.10183. Epub 2019 Apr 24. PMID: 31059080.