Use of performance-enhancing drugs by athletes and bodybuilders appears to be common in the UK. Although there are no comprehensive national figures, there is evidence that such drugs are also widely used in sections of the general and gym-using populations, in the expectation of physical and cosmetic benefits. Use of performance-enhancing drugs often takes place with little knowledge or acceptance of potential harmful effects, and clinicians in many settings may see patients who are experiencing problems related to such (usually covert) use. Here we consider medical aspects of performance-enhancing drugs.