Well, you do know the prime incredient in most allergy/cold meds is the main ingredient in the making of meth right?
Back to the op for a second: I've been on morphine 3 times in my life and not long enough to get addicted but having given up pot, alcohol, and other substances, I can say this without ANY reservations: a morphine high is THE best high I've ever had and can totally understand how people can get addicted to it. When I had knee surgery my doc asked if I wanted some in pill form and I declined. I said "that stuff is TOO good, I might be inclined to save it for recreational use" lol....