Great question, I've been asked this a zillion times (I'm a shrink). It depends on the person, and type and severity of their ADHD as well as the side effects they get. For young children with combined type (very hyper), everyday is a must. For mostly inattentive types, you can get away without it on weekends or days when you just dont need much focus. But it you have severe ADHD, going a day without it might cause unnecessary impulsive behaviors or problems with others. As far as side effects, if the stimulants cause too much weight loss, especially in people still growing, I find it important to try to either push nutritional shakes everyday, or skip the meds on weekends and breaks. Sometimes just a reduction in dose on those days can help the appetite come back, and sometimes help with sleep as well.