Um ... how's this ...
STOP TAKING IT NOW.
And you'll be totally fine, unharmed by what you've done for the rest of your life.
If you DON'T ... you might end up completely addicted, eventually moving on to oh, I dunno, smoking/shooting up crystal (a very similar drug, basically meth-amphetamine vs. dex-amphetamine), losing all your teeth, looking 30 years older than you are, with a damaged heart, brain, and other organs.
I speak from some level of experience, done plenty of ritalin and adderall and dexedrine over the years. I ended up doing crystal eventually because it was cheaper and easier to come by (and just as good a buzz). So I'm not just pulling this advice outta my rear end, okay?
LOTS of us 'played' with our drug of choice for YEARS before we finally got hopelessly addicted. NONE of us thought it would ever GO THAT FAR. No way, not US, why we're <insert some indication of 'specialness' here> and would NEVER become addicts.
Consider yourself lucky that you've become concerned about this problem in the early stages. Stop now, and you'll be fine.
Fail to do so, and you risk consequences.
That simple.