Clen is very anabolic in cattle, people used to use it on show bulls to get them to put on mass and get cut up. The receptors involved with clen respond very well in Cattle but with humans it is not very anabolic, we have different (and fewer) beta andregenic receptors. I've used it before, on and off for about a year, and all I can say about Clen is that it's good for giving you the jitters and some mean muscle cramps.
IMO it's a waste of money and it's something you should definately stay away from.