In Traditional Chinese Medicine (TCM), Hei Zhi Ma belongs to the 'Laxative herbs that drain downward' category. The herbs in this category are those whose main purpose is to treat constipation. They're called 'laxative' because they're often rich in oils. This allows them to lubricate the Intestines in order to help it remove the stools from the body.
Furthermore Hei Zhi Ma is Neutral in nature. This means that Hei Zhi Ma typically doesn't affect the balance in your body. Balance between Yin and Yang is a key health concept in TCM. Eating too many "Hot" (Yang) ingredients can lead to an imbalance whereby one has a Yang Excess. The inverse is true as well: too many "Cold" (Yin) ingredients can lead to a Yin Excess. The Neutral nature of Hei Zhi Ma means that you don't have to worry about that!
Hei Zhi Ma 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 Hei Zhi Ma 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 Hei Zhi Ma is thought to target the Kidney and the Liver. According to TCM, the Kidneys do not only regulate the urinary system but also play a key role in the reproductive system and the growth and aging process of the body. The Liver on the other hand 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.