I took the original jack3d nearly every day during the week and had weekends off, 2 scoop every time and was fine, great for workout, even had it when playing football and running around like a headless chicken lol
they then brought the new version without the DMAA and was weak and no good (Jacked3d Micro i think) , then i moved onto Craze which was good, then they also released Frenzy
its got bad name in the UK because someone died running a marathon and then later realised that person had heart issues
just take one scoop and see how you go, i never took more than 2 a time and waited 24 hours before the next one
a friend of mine got a jitters on one scoop and i had 2 scoops and never felt any jitters, just a great buzz and energy
you can always try a weaker pre workout and see how your body reacts to it first
Always good to cycle it as well, do it for a few weeks and then have a week or 2 off before your body gets used to it, then next thing u know u having 3 scoops lol