Which stimulants/eugeroics have a short (< 3 hours) half-life? I did some research into this. Nicotine and selegiline (~1.5 hours) are the shortest I could find. Methylphenidate comes in next (~3.5 hours), but that's longer than I'd like. I don't particularly like any of these choices for various reasons and am interested in learning about others. Alternatively, if there's a way to significantly reduce the half-life of modafinil, I'd like to hear about that.
I've considered amphetamine, armodafinil, atomoxetine, caffeine, ephedrine, methylphenidate, modafinil, nicotine, pseudoephedrine, and selegiline.
There are individual differences in metabolism rates of all drugs, so you might want to try some in the 3-5 hour range to see how they affect you. If tolerance worries you consider cycling some drugs or taking days off.
Nicotine could increase the clearance of caffeine as much as 50 %, you could use this to your advantage.
Consider raising your alertness nonpharmacologically, like exercise or cold showers for example. Consider working in an upright position.
In the other comment you said you have problems with sleep. There are several options to improve that ...
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