In Traditional Chinese Medicine (TCM), Xian Mao 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 Xian Mao is Hot in nature. This means that Xian Mao typically helps people who have too much "Cold" in their body. 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 Xian Mao can help restore a harmonious balance between Yin and Yang.
Xian Mao also tastes Pungent. 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 Xian Mao 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.
The tastes of ingredients in TCM also determine what Organs and Meridians they target. As such Xian Mao is thought to target the Spleen, the Kidney and the Liver. In TCM the Spleen assists with digestion, Blood coagulation and Fluids metabolism in the body. 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 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.