I know this is about Modafinil, but since many of you are commenting on Adderall and the various amphetamine salt mixes out there, I wanted to comment:
20mg of instant release Adderall daily (or worse, twice daily) is not a trivial amount to be taking. The long-term effects of the increased heart-rate and sudden spikes you will get from Adderall are not yet well studied or well understood in the medical community.
Stress, arterial stress, vasoconstriction[1], increased heart rate, and high blood pressure are all just a few of the things that happen when you take amphetamine salts. It's not just the jitters.
While these side-effects are okay from time to time, the body is not used to being treated this way on a daily basis, for years and years.
If you are in a place in your life where you don't think you need to be taking it, consider not taking it. Take a break on weekends, or a week at a time.
1: This is part of why many of you get "short" or "agitated" on these drugs... drink more water to at least help.