I've used jack3d before and did not notice any major side-effects, but that doesn't mean my body did not struggle. Mixing caffeine with creatine is just not a good idea. You need your water while working out extensively and caffeine is a diuretic. You may enjoy that little buzz while working out, but is it worth crashing for the rest of the day? Perhaps if you like to workout b4 bed or something. I don't know. Jack3d definitely isn't the best creatine out there by any means. I would choose any simple monohydrate over it.