Adderall is the first-choice drug for attention deficit hyperactivity disorder (ADHD), but you should always take it in the morning (avoid the afternoon); otherwise, it can cause difficulty falling asleep. It is an efficient drug and starts working within hours of taking it. But it is not safe for people who have pre-existing heart problems. Keep in mind that Adderall can be a habit-forming drug if you use it for a longer duration or in high doses.