Can this be legitimate?

My 18 yo son says he needs more. He is absolutely not selling it. (We live rurally and he doesn't have his license yet.)

When he takes it, it takes about 2 hours to start working and then wears off in6-8 hours, not 12. I can very clearly observe this, it's not just his perception. So he only gets about 5-6 hours benefit.

He was prescribed Adderall (not XR) to take in the afternoon, but that also wears off quickly.

We're new to all this and it's so frustrating. I don't know whst to believe or what to do. I have read that some people "burn through" it faster than others, and that makes sense to me. I've read that some people take more than 70mg. I don't know how they get it or if that's a really bad idea.