My experince of trying to get pain medication, that I ran out of (my home doctor can only prescribe a month's worth; gave me two post dated prescriptions to bring along) and one of them, you almost have to be terminal to get, the other not even in the country!
My wife (part of the reason why I love her) found an Argentine Doctor who would see me - he being a neurosurgeon at the Central Military Hospital. He was sympathetic to my my problem; it helped that I had a 7 page document from my doctor regarding my chronic pain issues; but even he could not write a prescription for the "closest" medication that I could use, Oxycontin. He called the Director of the Pain Management Clinic at the hospital, explained the problem, then walked us to her office. After about 10 minutes she wrote the three part prescription for me and we were on our way to the pharmacy that carried the meds.
Polostar - what Roxana says, and on some other threads, as I was told to do, go see an Argentine Doctor, take your prescription vial with you (to show you are using the medication) and ask for the prescription...my visit to the Central Military Hospital cost me the price of a cab there and the Subte back; then $45 US for the medication was well worth paying.