SARMs vs. Classic Anabolic Androgenic Steroids: Molecular, Pharmacokinetic and Safety Differences: A Narrative Review

Androgens regulate skeletal muscle, bone, erythropoiesis, and male reproductive function via the androgen receptor (AR), a ligand-dependent transcription factor. Pharmacologic modulation of AR has been pursued for clinical and non-medical purposes. Anabolic androgenic steroids (AAS), synthetic testosterone derivatives, act as full AR agonists, broadly activating multiple tissues. While effective in promoting muscle growth and strength, AAS cause well-known adverse effects, including hypothalamic–pituitary–gonadal (HPG) axis suppression, dyslipidemia, hepatotoxicity, cardiovascular disease, tendon injury, and neuropsychiatric disturbances. Selective androgen receptor modulators (SARMs) aim to stimulate AR in muscle and bone while minimizing androgenic effects in prostate and skin. They induce ligand-specific AR conformations, altering coactivator and corepressor recruitment, and avoiding metabolism by 5α-reductase or aromatase. Preclinical studies show favorable anabolic-to-androgenic ratios, but clinical translation is limited. Early human trials report modest lean mass gains, variable functional outcomes, and dose-dependent testosterone suppression. Emerging evidence also suggests cardiotoxicity, tendon injury, and liver toxicity, though long-term effects are unclear. Pharmacokinetically, SARMs have predictable oral absorption and moderate half-lives, enabling once-daily dosing, unlike AAS. This review compares AAS and SARMs in molecular mechanisms, pharmacokinetics, and safety. While SARMs offer partial tissue selectivity and reduced adverse effects, risks remain, and long-term safety is uncertain. Regulatory oversight is limited, and non-medical use is rising. Preclinical and clinical studies are needed to clarify whether SARMs can separate anabolic benefits from androgenic toxicity and inform safe clinical application.