Does Adderall become less effective over time?

It is quite common to develop a tolerance to Adderall. If and when it happens varies. Every few years, I've needed to increase my dose to be able to function. I would say yes, it becomes less effective over time for most people.

Yes, taking Adderall consistently for a long period of time will eventually build your brain's tolerance to it and the same dose may not be as effective as it once was. How long this takes depends on consistency and frequency of use, and obviously whether you continue to take the same dose or increase it. You can build a tolerance to it very, very quickly if you abuse it, like days or weeks. However, when used therapeutically, you'd probably have to be on your Adderall for the entire day, every day, for months to notice a significant tolerance.

No, actually one becomes more tolerant to the med needing to increase the dose, it happens with most meds in different drug classes.