I've tried xenadrine, hydroxycut and adipo kinetix. As far as the neck pain goes i haven't experienced any from thier use. I used them for fat-burning at first but now just to get jacked for lifting. I would suggest to cycle these thermogenics. The body has a high affinity to adapt to these stimulants. it's just like drinking coffee if you have it everyday you end up drinking more to get the same effects. I would use one for a couple of weeks and then switch brands maybe this will take care of your problem. I also heard that adipo kinetix was going to be taken off the market soon.