I'm a successful drug user in the sense I haven't died from it yet.
Personally, I've been through a lot when it comes to drugs. I'm only 20, I haven't had any hard addictions besides a 2 year long Opiate habit, but I know what it's like to be addicted to drugs. I feel even though I'm not addicted to them physically anymore, I still am mentally. Though, I don't think it's the drugs fault. It's one reason I hate when people say drug addiction is a disease. It's not a disease, it's a choice. A drug user chooses to get high, while a cancer patient didn't choose to have cancer.
Everyone has their fix though. Some people smoke cigarettes, some people drink a glass of wine at the end of the day. Some even rely on coffee or other forms of caffeine to get by. It's human nature to desire a change in our perception of reality. That's how it is for me, that's how I imagine it is for everyone else. It's fun, it's exciting, it's dangerous, it's all sorts of things. For some people, including me, I think it really comes down to a desire to self destruct. Some people do it to just feel good, some people do it because they hate themselves and want to not give so much of a fuck.