While the topic of using nootropics as an aid to concentration is surely debatable, the idea of using Amphetamine (Adderall) as a meditation aid is simply ridiculous. I use to take Adderall, as I was prescribed it for ADD. I also used to meditate on it, and while it did allow me to maintain focus on the breath quite well, the pleasant effects, the peacefulness, the calm, would not arise like does when I am sober. Adderall is highly potent, highly mind-altering. Nootropics are interesting as they are cognitive enhancers, but again I do not think that meditation is simply about being super-focused. How you approach meditation, and how you hold the meditation object, seems to be a fractal expression of how you handle all things in your life. Looking for shortcuts is not necessarily helpful. I may be wrong about this, but I'll take a guess that the search for a neurological understanding of Nibbana is a dead end.