Cinnamon Twig Decoction (Gui Zhi Tang, 桂枝汤) is a foundational formula in Traditional Chinese Medicine (TCM), first documented in the Shang Han Lun (Treatise on Cold Damage) by Zhang Zhongjing during the Eastern Han Dynasty (25–220 CE). This formula is renowned for its ability to harmonize the body's defensive (Wei) and nutritive (Ying) Qi, making it effective in treating various external Wind-Cold invasions, especially in individuals with underlying deficiencies.
