Aok, you have good questions, I think I can answer, excuse me if its not completely cohesive.
Your son likely does have ADD/ADHD, that is the most likely explanation for smoking crack (also a stimulant) making him calm instead of sped up.
People who actually do have ADD/ADHD tend to feel calm almost "zombie" like when they take stimulants, people without ADD/ADHD however feel very euphoric and sped up....So it makes sense that stimulants would not be something your son enjoys...Combine that with the fact children just hate taking pills and want to rebel for whatever reasons and it makes some sense.
Why would he want to use oxy and heroin if he spent years fighting the ritalin?
Well the oxy and the heroin (opiates) were probably much more enjoyable to him than stimulants, plus my guess is he was jealous watching how much euphoria all his friends got from stimulants but he for some reason he could not achieve.
Also, poor kids are lied to so much about drugs he probably thought, "hell im already on speed I can handle anything" not exactly, but felt a little stronger since he was experienced fighting ritalin.
People are often either speed people or opiate people when it comes down to it, your son is an opiate person. They are really different beasts.
I am also an opiate person, I can use speed once every month, take it or leave it, usually regret it afterwards.
Opiates however I have a weak spot for, I can understand alot of what he's going through.
I completely agree with that statement about those two drugs.
~What I'm curious about now is Ritalin. One of my sons is doing time because of heroin addiction. He was diagnosed with ADD/ADHD and mild OCD since he was 4. He hated taking Ritalin. When the nurse at school used to make him take it, she would have to inspect his mouth to make sure he swallowed it. He said he couldn't stand the way it made him feel, like a walking zombie. So why would he want to use oxy's and heroin if he spent years fighting the Ritalin? He also told me once that smoking crack made him feel calm. I told him how crazy that sounded. When my ex begged me to do it with him 25 years ago, the last thing I felt was calm! I wonder if that really happens to people with ADD? Anyone else out there experience that too? I'm very interested in finding that out.