It certainly varies a lot by person. Modafinil only really works for me if I take it once a week, max twice. Otherwise I seem to build some sort of tolerance.

It certainly varies a lot by person. Modafinil only really works for me if I take it once a week, max twice. Otherwise I seem to build some sort of tolerance. Also, when it wears off I very often get awful tension headaches and "mind fuzz", kind of like from caffeine but much worse. Unlike caffeine though, I can go a good 9 hours feeling energetic and only feel the pain once I get home and am done with the day, which is an advantage I suppose. Interestingly, I also seem to get fairly powerful euphoria for about 2 hours after it kicks in, which to my understanding is unusual. (And yes, I'm sure what I'm taking is really modafinil.) I only take it in "emergencies".