In Traditional Chinese Medicine (TCM), Jiu Cai Zi belongs to the 'Tonic herbs for Yang Deficiency' category. Tonic herbs are used for patterns of Deficiency, when one lacks one of the 'Four Treasures' (Qi, Blood, Yin and Yang). Yang Tonics are generally used in combination with a small amount of Yin tonics. If Yin is deficient, neither Qi nor Yang herbs alone will be effective. The most common symptoms associated with Yang Deficiency are low libido and impotence. It is worth mentioning that another very effective remedy against Yang Deficiency is regular exercise.
Furthermore Jiu Cai Zi is Warm in nature. This means that Jiu Cai Zi tends to help people who have too much 'Cold' in their body, although with less effect than a plant that would be Hot in nature. Balance between Yin and Yang is a key health concept in TCM. Those who have too much Cold in their body are said to either have a Yin Excess (because Yin is Cold in nature) or a Yang Deficiency (Yang is Hot in Nature). Depending on your condition Jiu Cai Zi can help restore a harmonious balance between Yin and Yang.
Jiu Cai Zi also tastes Pungent and 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. Pungent ingredients like Jiu Cai Zi tends to promote the circulations of Qi and Body Fluids. That's why for instance someone tends to sweat a lot when they eat spicy/pungent food. On the other hand Sweet ingredients tend 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 Jiu Cai Zi 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.