Bái Qián is a focused Lung herb used primarily for coughs with a lot of phlegm, wheezing, and chest congestion. It works by directing Lung Qi downward and breaking up accumulated phlegm, and is notably gentle compared to stronger cough herbs. It appears in many classical cough formulas and is especially helpful when breathing feels tight and phlegm rattles audibly in the throat.

'Descends Qi' is the core action of Bái Qián. The Lungs are supposed to send Qi downward (a function called 'descending and purifying'), but when phlegm or pathogenic factors block the airways, Lung Qi rebels upward, causing coughing, wheezing, and a sensation of fullness in the chest. Bái Qián redirects this rebellious Qi back downward, restoring the Lung's normal descending movement. As the classical Ben Cao Gang Mu states, Bái Qián 'excels at descending Qi' and is suited for conditions where the Lungs are congested with excess phlegm. This descending nature makes it complementary to herbs like Jié Gěng (Platycodon) that open the Lungs upward: one lifts and the other lowers, together restoring the full range of Lung function.

'Transforms Phlegm' means Bái Qián helps break down and expel accumulated phlegm from the airways. Its pungent taste disperses and moves stagnation, while its slightly warm nature helps dissolve cold, watery phlegm that can accumulate in the Lungs. Importantly, it is described as 'warm but not drying' (温而不燥), making it gentler than many other phlegm-resolving herbs. Because of this balanced quality, it can be used for both cold phlegm and, with appropriate combinations, even heat-related phlegm conditions.

'Stops cough and calms wheezing' follows directly from the two actions above. Once rebellious Qi is redirected downward and phlegm obstruction is cleared, coughing and wheezing naturally resolve. Bái Qián is particularly indicated when coughing is accompanied by an audible rattling of phlegm in the throat, chest fullness, and difficulty breathing.