This is a very ill-informed opinion. The supply chain is very strictly regulated for pharmaceutical medications.
Do you really think that Amazon can get their stock medications from just anyone? Do you think there is no oversight on this kind of thing? The DEA doesn't fuck around. They take all of this stuff very seriously.
Commingling medications? Really? In a pharmacy, medications are NEVER allowed to be commingled. If your medication is coming from two different manufacturers, or even the same manufacturer but the pills just look different, the pharmacy must put them in two different bottles to give to you. Stock bottle are not allowed to be mixed together. Ever heard of a recall on medications? That is exactly why. When a recall happens, they need tedious records of where every pill went.
When a prescriptions for a schedule II drug is filled, the pharmacy technician has to count the number of pills being filled twice. Then the pharmacist has to count the number of pills, and then backcount the stock bottle to make sure everything is kosher and no pills are missing.
I understand not everyone knows everything about the pharmaceutical industry, my wife is a pharmacist is the reason I know as much as I do, but to think that there is that little oversight on pharmaceuticals is ludicrous.