Hi Health.
It is very misleading to make a statement that all medicines are natural. And it is exploitive to bend the term in this context just to prove a point.
In law, they select a desired conclusion and then bend the story to fit. In science, the facts should determine what the conclusion is.
In the sense that everything in the universe is natural, you are correct. In fact, even feces is natural, but it is poison. Uranium is natural.
A valid definition and understanding of the word “natural” would render prescription drugs as unnatural, especially in comparison to the holistic, organic, and non-genetically modified substances used in alternative/complementary health care, as well as other modes of “alternative” care.
The primary reason is, whether there is tree bark or whatever in the substance, the molecules of those ingredients are altered, modified, synthesized to where they can be considered anything but “natural”, and the manufacturers even admit such by claiming the benefits outweigh the risks.
And it is by that broader understanding, that there is a valid claim to be made that scripts are not natural.