I have read a few articles recently that mention that the so-called active constituents of many Chinese herbs have very low bioavailability in real-life use cases. A well-known example is Turmeric. Very little of the curcumin in Turmeric enters the general circulation. However, it has long been known to have a direct anti-inflammatory effect on the tissues of the GI tract that it comes in direct contact with. This article suggests that various microbiota might act on various Chinese herbs in a way that has systemic physiological effects that would not have occurred without such mediation. Interesting stuff.
Read on www.sciencedirect.com/science/article/abs/pii/S037887411530283X