Back when I lived in the boondocks, the county I lived in had two mom and pop pharmacies and no large ones. Once in a while they would try to switch my Fentanyl patch and it was always because they were out of what I normally took. I couldn't use the Watson brand because they made me break out so I had my pharmacist buy my brand from the pharmacy down the road and then resell it to me. Perfectly legal. Otherwise, I would need to get permission from my pain doc to use a different pharmacy per my drug contract.