They’ve caused global scandals. They’re banned  in most athletic competitions. But are steroids actually bad for you? The term “steroids” refers  to a broad category of molecules that share a similar molecular structure, but have many different functions. When people talk about steroids  in the context of sports, they’re referring to a subset of steroids that resemble testosterone. Though elite athletes and bodybuilders began using these steroids in the 1950s, today, most steroid users  are actually not competitive athletes, but people seeking  a particular appearance. These steroids have two main effects:  androgenic, or masculinizing, and anabolic, or growth-promoting. These effects mimic naturally-occurring  testosterone, which drives the development  and maintenance of male secondary sex characteristics and general growth in everyone. That means testosterone  and the synthetic steroids based on it promote body and facial hair growth, enlargement of the vocal cords and deepening of the voice,  increased muscle mass and strength, and increased stature and bone mass. Recreational steroid users are after the anabolic, growth promoting effects. To make muscles grow, steroids  first promote protein synthesis— proteins are essential building blocks of all cells, tissues, and organs, including muscles. Steroids also block cortisol, a signaling molecule that drives  the breakdown of substances including proteins. Finally, they may push the development of muscle, rather than fat, and boost our metabolism, shrinking fat deposits. These properties make steroids valuable for treating many illnesses and injuries. They can help people  with wasting illnesses, like AIDS and certain cancers, maintain muscle mass and help burn victims recover lost muscle tissue. So if steroids are used as medicine, they must be safe to use recreationally,  right? Well, it’s not that simple. To create the desired muscle growth, recreational steroid users must typically take doses orders of magnitude higher than those prescribed for a medical condition. Long term, high dose steroid usage can have both undesirable and outright harmful effects— some of them dependent  on factors like age, sex, and underlying health conditions. We’re not sure  what all the risk factors are, but we do know recreational steroid use is particularly risky for adolescents. During puberty, steroid use  can prompt bones to mature before they’re done growing, causing growth defects. Adolescents are also most at risk for the harmful psychiatric effects  of steroid use. The most common of these, increased impulsivity and increased aggression, are well-known as “roid rage.” Up to 60% of users  experience these effects. But there are also less common, more damaging psychiatric side effects like mania and even psychosis. Steroid use can damage organs  including the liver and kidneys, and cause cardiovascular problems like high blood pressure. While some or all of those effects  may be reversible, steroid use can also cause liver cancer, especially in males. Though recreational users take steroids for their anabolic effects, they also experience androgenic effects— often undesired. That can mean increased body hair, enlargement of the clitoris, and permanent voice deepening in females. At the same time, excess testosterone-like steroids can cause feminization in males, because the body converts  the excess into estrogen. This can lead to breast development and shrinking testicles. These effects are not uncommon— about a third of male steroid users  experience them to some degree. Excess steroid use can also reduce fertility in males and females— by reducing the sperm in semen or  by causing missed periods and conditions like polycystic ovary syndrome. All these effects may be reversible  if steroid use stops— but they may not be. The specific steroid, the duration of use, and other factors could play  a role in reversibility. Finally, there’s mounting evidence that users are susceptible to steroid dependence. They can develop tolerance and require increasingly large doses over time. This increases the risk  of harmful effects, all of which are increasingly common  at higher doses taken for longer durations. Still, there remains little definitive  information on how common and how reversible almost any of the harms are at different levels of use. We don’t know enough, about  either risk factors or exposure levels, to definitively say any recreational  steroid use will be harm-free.