throw some tobacco leaves (or any other drug that comes in plant form) on a fire

That is most likely. In many cultures however, you'll find a lot of folklore where legendary/mythic figures are given credit for developing medicine. In the case of TCM at least, there has actually developed a complex system based on basic axioms of human health and physiology as it relates to our living environment and a set of metaphysical principles about the nature of reality. Traditional pharmacists/physicans go about a systematic way of characterizing and using various materials to cure illnesses and treat physical conditions. Evidence-based methods of western science has revealed that as kooky as much of it can be, there is often a scientific basis for the effectiveness of a great deal of this body of knowledge. In other words, the basic science may have been off or even completely wrong, but trial/error and repeated application (with adjustments) of a crude form of the scientific method actually produces results that are useful.