SUMMARYColloquially referred to by various misleading monikers ('pro-hormones', 'natural steroids', 'testosterone boosters', etc.) designer anabolic steroids have been popular now for over a decade as a way to achieve classic anabolic steroid-like results from products sold in the legal marketplace. Recent evidence suggests that anabolic steroid use may be the most common cause of hypogonadism in men of reproductive age. Despite recent regulatory efforts that have banned specific compounds, many anabolic-androgenic steroids (AAS) remain available in over-the-counter dietary supplements that are legally sold in the United States. Severe side effects including hepatotoxicity, cholestasis, renal failure, hypogonadism, gynecomastia, and infertility have been reported secondary to the use of these products. While some of these side effects may be reversible, more aggressive use may result in more permanent end-organ damage as has been previously described for the case of aggressive AAS users (Rahnema et al., Fertil Steril, 2014). Designer AAS remain easily available for purchase in over-the-counter bodybuilding supplements and these products appear to be increasingly popular, despite the known health risks associated with their use. We conducted a systematic search to identify the designer steroids that are most commonly sold in dietary supplements as of April 2014 and review what is known regarding their potency and toxicity. We propose that the impact of AAS use on the reproductive and hormonal health of men is underestimated in the literature owing to previous studies' failure to account for designer steroid use. Lastly, we make clinical recommendations to help physicians steer patients away from potentially harmful supplements, and summarize key regulatory obstacles that have allowed potent androgens to remain unregulated in the legal marketplace.