Selective androgen receptor modulators (SARMs) and selective estrogen receptor modulators (SERMs) are performance-enhancing drugs used by doping athletes to stimulate anabolism and thereby increase muscle mass, strength, and recovery from exercise training. SARMs are intended to have the same effects as androgenic anabolic drugs such as steroids and hormones such as testosterone. SERMs act as estrogen receptor agonists or antagonists depending on the type of tissue; they interfere with the negative feedback loop of the hypothalamic–pituitary–gonadal axis, thereby allowing testosterone levels to rise, and so are used mainly by male athletes. Animal data support the assumption of physiological and performance enhancement by SARMs and SERMs, but human data are less conclusive. These drugs are banned by the World Anti-Doping Agency. Both types have detrimental side effects but not to the extent seen with more potent anabolic agents such as testosterone and steroids.