What role does Rhizoma Coptidis play when taking medicine?

The ancient book "Medicinal Nature Fu" contains: Xuan Huanglian treats cold-heat dysentery and thickens the stomach to stop diarrhea.

Upstairs (you were under me, but I changed, so I am below. HOHO~) ... Chinese medicine pays attention to compatibility, and the combination of the two drugs can improve the curative effect or enhance the medicinal properties and reduce the side effects. This compatibility is called soul mate, soul mate. If a single medicine is used to treat diseases, it is just a folk prescription ... there is no prescription but medicine.