I've taken clen. It has no problem working for me. Low doses (i.e. 40mcg) I generally don't "feel" anything per se, but i know its working. My water weight drops pretty quickly in the beginning. Higher dosages (i.e. over 40 mcg) and I can feel some shakes and a couple other side effects, and the clen still works for me. I'd rather take smaller dosages. Keep in mind if your diet is not in check, the clen won't do anything for you.