I used clen a handful of times from different brands. The only brand that really shined for me was malay tiger's clenox. I don't know what they put in there but i thinks there's more than clen alone...
Turns out they are overdosed when i looked up on the internet and found some old posts on it. I never found any clen that had the same effect...
It turned me into a stage ready conditioned freak after 4 weeks of use. I was bulky at 16% and it turned me into this zyzz/jeff seid type of look really quick.
This is why i think clen is so abused and loved in the bodybuilding community. The drugs is not only good for fat loss but the muscle mind connection is crazy as well.
I've not only burned fat but build muscle on it as well. It's a great anti-catabolic drug and if you eat clean you can recomp on it pretty well...
But then again i tried clen from other brands that were weaker or where effects are non existent...
Nowadays i've become more prudent for my heart though. I know the shit is cardiotoxic and we all know what that means. Taking clen is tempting but is it really worth the risk? If you wanna get lean just do some caffeine with some green tea extract or pure EGCG. DO your fucking cardio and eat clean.