Clen is Clenbuterol. I've never used it and you can't ask on this forum where to get it. Clenbuterol is considered a research chemical. Research chemicals are not for human consumption. There are many Research chemical companies out there. A google search will point you in the right direction. I'll pull up some info on it for you.
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You can search hundreds of threads on this forum in regards to Clenbuterol.
You could also consider an ECA stack(Ephedra, Caffeine, Aspirin.) Search that
An ECY stack(Ephedra, Caffeine, Yohimbine) Seach that
I've used Leviathan Reloaded with good results, DCP, ECA with good results.
Alot of people won't touch Clen because of some of the side effects listed in that post I have up there.