归经

Channel tropism (归经, guī jīng) is the third of the three primary attributes of every Chinese herb, alongside nature and flavor. It expresses the observation that an herb does not act on the body uniformly — instead, its effects are most pronounced in particular organs or along particular meridians. Platycodon (桔梗, Jié Gěng) is said to enter the Lung channel, and so it benefits the Lung qi, transforms phlegm, and stops cough. Chinese angelica (当归, Dāng Guī) enters the Liver, Heart, and Spleen channels, and so it tonifies Liver-blood, nourishes Heart-blood, and supplements Spleen-blood.

The channel tropism of an herb has historically been determined empirically: physicians observed which symptoms an herb reliably treated, identified the organ system to which those symptoms belonged, and inferred that the herb "enters" the channel of that organ. An herb that effectively treats red, swollen, painful eyes is taken to enter the Liver channel, since the eyes are the orifice of the Liver. An herb that calms cough and wheezing enters the Lung channel, since the Lung governs qi and respiration. Channel tropism is therefore a pragmatic clinical category, derived from outcomes, rather than a claim about the herb's anatomical distribution.

Channel tropism transforms an herb from a generic tool into a targeting key. Two herbs may share the same fundamental action — say, tonifying qi — but enter different channels and so be used in different clinical situations. Astragalus (黄芪, Huáng Qí) tonifies qi but enters chiefly the Spleen and Lung, making it the herb of choice for Spleen-qi and Lung-qi vacuity. Ginseng (人参, Rén Shēn) also tonifies qi but enters the Spleen, Lung, and Heart, so it both tonifies qi and calms the spirit. Among the heat-clearing bitter herbs, coptis (Huáng Lián) enters the Heart and Stomach (clearing Heart and Stomach fire), scutellaria (Huáng Qín) enters the Lung and Gallbladder (clearing Lung and Gallbladder heat), and phellodendron (黄柏, Huáng Bǎi) enters the Kidney and Bladder (clearing damp-heat in the lower burner). When constructing a formula, the practitioner uses channel tropism to direct each ingredient to the part of the body where it is needed.