First, Adderall and Ritalin are similar, but not the same. Both are prescribed for long-term use to treat ADHD and narcolepsy, and both are available in multiple dosages, in both ordinary tablets and extended-release capsules. They are central nervous system stimulants and increase the availability of two neurotransmitters, dopamine, and norepinephrine, essentially “speeding up” brain activity. Ritalin works faster and has a shorter half-life in the body than Adderall.
The choice of Ritalin or Adderall depends upon how important long-acting performance is (in which case Adderall is usually preferred) and the desire to keep side effects to a minimum (in which case Ritalin is usually preferred). The two drugs cost about the same, and generics are available for both.