The best-known PEDS are anabolic androgenic steroids (AAS), which are close chemical cousins of testosterone, the chief male sex hormone. Athletes take them to increase the size and strength of their muscles, and for their purported ability to enhance recovery after exercise, which allows people to train harder than would otherwise be possible. Though ethical issues make studies tricky to do, steroids' strength-enhancing effects have been confirmed by several research projects.
The most thorough trials on their effects on sport were conducted in East Germany, which ran a state-sponsored doping programme that began in the 1960s. After the fall of the Berlin Wall, data collected by this project became available to independent scientists, and were written up in1997 in a paper published in Clinical Chemistry. One early test subject, a female shot-putter known only as "1/68", improved her best performance from 18 metres to almost 20 metres—close to the world record at the time—within 11 weeks of beginning a cycle of Turinabol, a synthetic AAS developed in 1961. AAS proved particularly potent in women, presumably because they start with lower levels of testosterone than men and therefore have more scope for enhancement. A report delivered in 1977 to the Stasi, East Germany's secret police, reported improvements in female athletes' performances of up to five metres in the shot put, 20 metres in the discus, five seconds in the 400-metre sprint and ten seconds in the 1,500 metres.
After anabolic steroids, the best-known doping drug is probably EPO, a natural substance which stimulates production of red blood cells. An artificial version was developed in the late 1980s to treat anaemia. It (and its chemical cousins) quickly became rampant in endurance sports such as running and cycling. Red blood cells transport oxygen around the body, and the supply of oxygen to an athlete's muscles is an important limiting factor in endurance exercise. So boosting red-blood-cell counts can allow superhuman efforts.