In Traditional Chinese Medicine (TCM), Da Huang belongs to the 'Purgative herbs that drain downward' category. The herbs in this category are those whose main purpose is to treat constipation. The fact they're 'purgative' means that they do so by removing Excess Heat in the Intestines and/or Stomach. As such all herbs in this category are Cold in nature, in order to cool the Heat.
Furthermore Da Huang is Cold in nature. This means that Da Huang 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 Da Huang can help restore a harmonious balance between Yin and Yang.
Da Huang also tastes Bitter. 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. Bitter ingredients like Da Huang tends to have a cleansing action on the body by clearing Heat, drying Dampness and promoting elimination via urination or bowel movements.
The tastes of ingredients in TCM also determine what Organs and Meridians they target. As such Da Huang is thought to target the Spleen, the Stomach, the Large intestine, the Liver and the Pericardium. In TCM the Spleen assists with digestion, Blood coagulation and Fluids metabolism in the body. The Stomach on the other hand is responsible for receiving and ripening ingested food and fluids. It is also tasked with descending the digested elements downwards to the Small Intestine. 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. The Liver is often referred as the body's "general" because it is in charge of regulating the movements of Qi and the Body Fluids. It also takes a leading role in balancing our emotions. The Pericardium is also called the "heart protector". It is the first line of defence for the Heart against external pathogenic influences