I threw my last pack away last year, due to the emergence of a nasty side effect. I'd used it to power through a few insane projects, and had what I would call a decent "honeymoon period": get up at 4am, brain so groggy it was hard to tie my shoelaces, pop 100mg and within 30 minutes I'd be hyper-awake, clear headed and have laser sharp focus. The euphoria he mentions was nothing mild for me either, it really wasn't far off something like cocaine or ecstacy (minus accompanying loss of faculty).

Then gradually another feeling started accompanying it, which I can only describe as a "darkening" of my perception of the world, and strong sense of impending doom which became intrusive and hard to ignore (to the detriment of whatever task was at hand). It rendered me mildly depressed and highly anxious at the same time (although only for about 12-14 hours), and it did so consistently. I've never heard anyone else mention such an effect, but if anyone starts feeling a bit like that (and for me it was frankly a powerful and rather scary side-effect), consider whether the drug is to blame.