Seriously - if any of these Ritalin / Adderall etc help you think clearly and do more than just let you work on less sleep, you most likely have ADD, and can treat it in a structured way with a doctor helping you, instead of ad-hoc self medication.
People without ADD experience significant benefits from using Adderall because it's an amphetamine--not because they have undiagnosed ADD.
Any amphetamine helps you think clearly through being more alert and ability to concentrate for longer periods of time.