It doesn't break muscle tissue by itself, but when you diet you will tend to go into a negative nitrogen balance - in some states even ketosis (especially post workout/cardio) - which can cause muscle loss. Just keep the dosage low, ramp up slowly, go 2 weeks on 2 weeks off and make sure your diet is high in protein.
As to my experience, I have gotten cramps with clen, so I usually have a lot of aids such as potassium that I use 2-3 times a day to help keep me hydrated.
Mr.X