I came to the same conclusion after taking modafinil daily for 5 months. I quit because I was getting completely drained by 7pm. I had to hit the bed as soon as I got home, and then slept for 10-12 hours straight. I did the arithmetic and it wasn't worth it. Supposedly, there isn't such thing as a "modafinil withdrawal," but I was nonfunctional for about 6 weeks after I left it cold turkey. Not only that, but because I wasn't aware there was a withdrawal phase, I thought my symptoms (not being able to wake up, narcolepsy, nausea) were an ominous sign of an underlying disease.
Taking modafinil daily, especially for that amount of time was not a wise move. It's a uniquely "safe" substance but even the most avowed users stress not to take it daily even if for nothing more to preserve perceived effectiveness.
That was four years ago, and I was back to my baseline self in about two months.
A month ago I was diagnosed with severe apnea, and since starting treatment I feel like a different person. I wonder whether the apnea was worsened by modafinil four years ago, and that was the reason for my constant wearing down. Maybe I'll do an experiment just to see, but I don't need stimulants anymore to be productive, not even coffee.
