I'd think hard about the possible consequences of doing this. It could be challenging to explain if you're ever asked about it when undergoing official diagnosis, you might be forced to lie or risk being labeled a drug seeker.
And I don't think looking out for whether it "helps you concentrate" is a valuable metric. Healthy people also abuse stimulants because it helps them concentrate.
Perhaps a more valuable effect to pay attention to is whether it calms you down? This is a counter-intuitive effect common in people with ADHD.
