For repurposing candidates, the complication is that they usually refer to pharmaceutical company compounds offered for repurposing because the clinical development was halted (i.e. failed) for their intended indication but they had a safe Phase I result profile. This is distinct from reports of approved drugs being successfully repurposed because (by definition) these candidates were unsuccessful in the first place. The subject of vendor compound offerings might seem peripheral but from practical point of view they are important because it is certain that some of them will be used in experiments related to ADEV investigations where they can serve as reference compounds, negative controls or for comparative system perturbation. As a quality vendor of stock compounds (as opposed to large-scale brokerage operations) Tocris provides a good example of a targetcentric specialist reagent supplier with 6190 links to PubChem CIDs, of which 1876 are also However, as already alluded to, there are caveats associated with probe classification and choice even with quality vendors. For example, from the 218 CID entries for the historical non-probes mentioned above 72 are listed by Tocris, 98 by GtoPdb and 49 by both. To be rigorous these are not explicitly endorsed as probes by either of these sources but the publications (which may have declared them as probes) have passed the threshold for curation in each case.