Clen is both catabolic and anabolic in nature but it's anabolic tendencies slightly out weigh it's catabolic (protein degradation) tendencies-hence tipping the scales in favor of anabolism (protein retention). Not by a large degree, but enough to make a difference over time. To prove my point-I have put females on clen and they began experiencing additional muscle growth after 6-9 months of use without the assistance of anabolic steroids.