I've used a ton of clen over the years and mostly veterinary sourced from the local horse race track.lol I never took the breaks from clen, but used it more as a long term pre-workout instead of my favourite which is the ephedrine/caffeinne stack. I never used it for dieting, just as a pre-workout and now nothing else will work.haha If you want to know about clen, hit me up with a PM and I can probably help with that end of things. Clen just doesnt have the original kick that ephedrine gives before the workouts. However, clen over time it works very well with diet and seems to stay effective for a longer period but I'm not sure of the half life of it in your system. just my 2cnts.