A better idea is to pace yourself.
Set aside regular breaks in your study to go outside and do something physical. Get your heart rate up, the usual 30 minutes of exercise - this will stimulate blood flow to your brain. It has the added bonus of letting your subconscious think about what youve just been studying, while your conscious mind works on jogging/cycling/swimming/whatever you're doing.
Have plenty of fruit available while you study - the fructose is still sugar to give you the energy to keep studying, but its better for you than sugary food sugar.
Maybe write yourself a timetable - 60 mins study, 10 minute break, 60 minute study, 30 min exercise... and so forth.
You need to give your brain time to process all this information, instead of stimulants to drag you through longer study sessions where you lose effectiveness.
Most human brains can only learn effectively in blocks of about 50-60 minutes at a time, after which you need a short break to refresh.