Effects of long-term adderall use?

I'm 25 now, but since I was 15, I've been prescribed adderall. First it was the regular, 10 mg twice a day. Then when I was about 20, I got switched to 20 mg XR. I took it on and off for four years or so, and then about a year ago I felt that it might be dangerous to take it all the time, but i still needed it so i just started taking 10 mg. It worked for a while, but then It stopped working pretty much completely, so I started taking the 10s twice a day. It still doesn't work that well--I can fall asleep on it, right after I take it! So I got my prescription switched back to the 20mg....now I take either that or I take a couple of the tens. I often take it before I go to bed, because it helps me wake up in the morning! Is this bad?? I use it to stay up and work a lot, which isn't it's intended use really.... So what I'm wondering, is how bad is it to kind-of misuse adderall (on & off) for ten years or more? Could It really be effecting me and I don't realize it? Am I going to suddenly have a heart attack one day? (I never take more than a 30-40 mg a day, and even that much is kind of rare....usually 20 mg). Should I just take the standard 20 every day? How long would it take me to detox, so when I take just 20 mg every day, it actually works like it used to?? Sorry for all the questions, please help. :) Thanks.