山栀子 (Shan Zhi Zi) or simply 栀子 (Zhi Zi) is a well known Chinese medicinal. The fruit is the primary part used in medicine and can be found in early materia medicas such as the Shen Nong Ben Cao （神农本草）and the Ming Yi Bie Lu （名医别录）。
Gardenia jasminoides (Ellis) is a sub-tropical and tropical shrub and small tree of the Rubiaceae plant family, also known as the Coffee family. Two great plants, one big family. This plant family is also sometimes referred to as the Bedstraw Family and this relates to plants like Galium aparine (Cleavers), which can be found in my book，and Rubia cortifolia (茜草, qian cao) and many other Chinese medicinals.
Gardenia fruits are bitter, cold and enter the heart, liver, lung, stomach and the triple burner channels. It is used to drain fire and eliminate vexation, clear heat and disinhibit dampness, and cool blood and resolve toxin (中药学，Zhong Yao Xue, 2002, pg. 74). The Shen Nong Ben Cao Jing, mentioned above states that this herb treats evil qi in the five internal organs. The Ming Yi Bie Lu, also mentioned above, states that it treats red and painful eyes due to heat, heat in the chest, heart, small and large intestines, heat in the stomach, as well as vexation and oppression in the chest/heart region. This last indication is repeated by many authors and has significant clinical applicability today.
Modern culture has lead to over-work, over-eating, lack of sleep, lack of exercise, and the ingestion of various toxins from the air, water, food, etc. These factors combined lead many to have significant stress-related complaints. Stress often leads to depression of the qi dynamic, which eventually leads to blood stagnation, both of which will lead to heat. Since the heart is the commander of blood the house of the spirit/mind, the combination of blood stasis and qi stagnation with the stressful life so many people lead, vexation and oppression in the chest is a relatively common complaint. Gardenia treats this as well as any herb I know, or better, and is a great addition to so many formulas. Additionally, from an ecological point of view, this medicine comes from a fruit that is easily cultivated and thus there is little to no threat to the sustainability of using this plant as medicine.