Most energy drinks contain high doses of B vitamins. B vitamin deficiency causes fatigue, weakness, and depression. I'm not sure if mild B vitamin deficiency is common or if very high doses do the opposite, but I've noticed a bigger mental boost from some energy drinks than from a similar amount of caffeine without the vitamins.
Taurine a stimulant? I thought that's a relaxing aminoacid they put there so you won't get too nervous with all that caffeine.
Sorry, taurine is not actually a stimulant even though it is commonly referred to as such.
If you're willing to branch out into other stimulants, I'd strongly recommend Kratom, feel free to ask if you have any questions.