This is our standard disclaimer for statements about drugs, experimental compounds, bioactives, biogenics and metabolites.
We use a "annotate by delegation" model to arrive at conclusions about the biological activity and biogenic origin of compounds. Specifically, we assign curated catalogs to one of these categories, from which we infer, categorically, how compounds should be classified.
Thus, if a compound is in HMDB Endogenous, it is classed an endogenous human metabolite. Similarly, if it is in DrugBank illicit, we classify it as having been "in man". If a single or a few compound(s) turns out to be incorrectly classified, we will inform the source catalog curator, and await a catalog update to apply the change to ZINC.
If there are more than a few misclassifications, we may re-assign the catalog into another category. Were this to happen, it would likely be due to our misunderstanding. If you suspect this has happened, please let us know and we will attempt to address the problem promptly. Thus for instance, imagine we misclassified ChEMBL19 as "bioactive", (drug=2) but it really should have been "in an annotated catalog" (drug=1). This change is simple to make.