CVS, Walgreens, and Walmart all know how much stock they are buying and selling. We aren't talking about denying individuals as much as whistleblowing on trans changes in addictive prescriptions. We're talking about the big pharmacies being culpable with Purdue Pharma.
I think you are looking for the FDA which oversees "legal" drugs whereas the DEA is largely focuses on "illegal" drugs. Quotes because context matters