It sounds very much like your problem is the same one students have a couple of months before their exams. Googling it seems that their study drug of choice is something called Modafinil with somewhere between 20% and 25% of students at some British universities supposedly using it to help them study in the weeks leading up to their exams.
There is some published research which suggests it might help.
RESULTS: Improvements under modafinil were seen on spatial working
memory, planning and decision making at the most difficult levels, as
well as visual pattern recognition memory following delay. Subjective
ratings of enjoyment of task performance were significantly greater
under modafinil compared with placebo, but mood ratings overall were
not affected. The effects of modafinil on creativity were inconsistent
and did not reach statistical significance.
CONCLUSIONS: Modafinil reliably enhanced task enjoyment and
performance on several cognitive tests of planning and working memory,
but did not improve paired associates learning. The findings confirm
that modafinil can enhance aspects of highly demanding cognitive
performance in non-sleep deprived individuals. This article is part of
a Special Issue entitled 'Cognitive Enhancers'.
But you should note that Modafinil is on the list of FIDE banned substances along with amphetamines (including ADHD drugs like Ritalin and Adderall), ephedrine (common in over the counter nasal decongestants - a few years ago a Scottish skier lost his Olympic bronze medal due to use of a nasal spray he bought in a pharmacy), caffeine and codeine.
Personally I'm a bit skeptical. If you woke up in the morning and took one of these and immediately opened your book of rook and pawn endgames then it might work. But if you logged on to an online chess site and started playing blitz you might be stuck there for 8 hours! Oh, wait, that second scenario happens all the time (or at least until it's time for lunch).