It will depend, it could even be a drug that is out there but being used for something else. For example, some of the older antidepressants (to treat depression) are being used to treat nerve pain (though in smaller doses). Certain chemotherapy treatments, in smaller doses, are being used to treat inflammatory disease (rheumatoid arthritis).
In terms of drugs coming from natural products, flower petals are not that far off. Aspirin (used to treat pain) came from the leaves of the willow tree.