With regard to the limit on quantity, referred to by Barsel above, while ordinary shops are only allowed to sell 32 tablets at a time, pharmacies can sell bigger quantities.
For example, when I was booked in for a hospital op, I was advised to stock up on both paracetamol and ibuprofen to take for quite some time afterwards. I thought the limit was 32 tablets of each but, when I tried to purchase that many at the self-service checkout in Morrison's, I found out that the limit was actually a total of 32 tablets. (16 of each).
However when I walked just a few metres from the checkout, the in-store pharmacist was happy to sell me as many tablet as I thought that I might need once I explained my situation to her.
(As it turned out, I never had even the slightest twinge of pain after my op, either in hospital or when I got home!)