I found methylphenidate-based drugs to be useless after a few days.

Have you tried pure lis or dexamphetamine? I know dex can be prescribed without the mixture, maybe lis can too. I keep meaning to ask my doctor about it.

The other issue I find is tolerance, though even with this I'm still far more focused than when I'm not taking adderall. It really is amazing how much better it makes me feel. I find no problem with addiction whatsoever -- if I forget to take it, then I just have full blown ADHD, but I'm no worse off. I also find it's more effective if I minimize coffee, but I haven't yet cut coffee entirely. (I find caffeine is vastly more addictive than amphetamines.)