In Traditional Chinese Medicine (TCM), Gua Lou belongs to the 'Cool herbs that transform Phlegm and stop Cough' category. In TCM Phlegm is a condition of Stagnation of Fluids which tends to start in the Spleen and then goes to the Lungs. If this overly accumulates it thickens and becomes pathological Phlegm. Phlegm, being a form of Stagnation, often starts as being Cool and transforms to Hot as the condition progresses. The herbs in this category are Cold in nature so they treat the later stages of the Stagnation: Hot and Dry-Phlegm with symptoms such as cough, goiter or scrofula.

As suggested by its category Gua Lou is Cold in nature. This means that Gua Lou typically helps people who have too much 'Heat' in their body. Balance between Yin and Yang is a key health concept in TCM. Those who have too much Heat in their body are said to either have a Yang Excess (because Yang is Hot in nature) or a Yin deficiency (Yin is Cold in Nature). Depending on your condition Gua Lou can help restore a harmonious balance between Yin and Yang.

Gua Lou also tastes Sweet. The so-called 'Five Phases' theory in Chinese Medicine states that the taste of TCM ingredients is a key determinant of their action in the body. Sweet ingredients like Gua Lou tends to slow down acute reactions and detoxify the body. They also have a tonic effect because they replenish Qi and Blood.

The tastes of ingredients in TCM also determine what Organs and Meridians they target. As such Gua Lou is thought to target the Large intestine, the Lung and the Stomach. In TCM the Large Intestine receives the "impure" parts of the digested food from the Small Intestine, absorbs the remaining fluids and excrete the remainder as feces. In addition to performing respiration, the Lungs are thought in TCM to be a key part of the production chain for Qi and the Body Fluids that nourish the body. The Stomach is responsible for receiving and ripening ingested food and fluids. It is also tasked with descending the digested elements downwards to the Small Intestine.