Andarine, also known as S4, is a selective androgen receptor modulator (SARM). It is similar to anabolic steroids in that it can increase muscle mass and bone density, but it is not as potent or harmful as steroids. Andarine is used in the treatment of osteoporosis and other conditions related to muscle wasting. It is also sometimes used by athletes and bodybuilders to improve athletic performance and build muscle.

It is important to note that Andarine is not approved by the FDA for use in the United States and its safety and efficacy have not been fully studied. It is also a controlled substance in some countries and can have serious side effects if used improperly or without medical supervision