Ritalin
"I've been taking methylphenidate (Ritalin) for years. I started during my professional career, because according to my psych, I am "too smart to sit still", and that because of that, my brain gets bored easily then my attention span fades. With Ritalin I can focus like a laser on tasks, get much more done, stay organized, and it also helps with that afternoon sleepiness. Added bonus is it revs up your basal metabolic rate, and reduces appetite so you can lose weight easily.

Downside, it increases BP. If you have high BP you may want to avoid it.

I take a 20 mg pill 3-4 times a day, never after dinner if you want to sleep."