We'd never endorse doping, but leaving it off this list would be remiss. It's a serious offense that violates the World Anti-Doping Code, but it does occur. Nearly all major sports organizations and a large number of nations accept the code as standard [source: WADA].
Athletes were first tested for doping at the 1968 Mexico City games, and the system has evolved since then. Nowadays the International Testing Standard, as determined by the World Anti-Doping Agency (WADA), dictates the process run like this: Blood or urine samples are collected at times that optimize the detection of doping. Athletes don't get advanced notice. If they refuse to provide a sample, in almost all situations, it's considered a violation of the code. If they fail to be available for a sample, in certain cases they can be allowed three such failures in an 18-month period before they are deemed to be in violation. Evading a test or tampering with a sample also results in violation as does, of course, being proven to have been doping. Athletes are required to remain with the doping control officer (or chaperone) at all times until a sample is provided.
Some athletes are subject to random testing, others are targeted. An athlete might be targeted for several reasons, like an atypical physique, behavioral oddities or unexpected withdrawal from a competition.
The prohibited substance list is divided into three sections: items that are always prohibited, only during competition or only in particular sports. The list reads like a chemistry book, but some of the generalized examples of universally prohibited items are anabolic androgenic steroids, growth hormones, aromatase inhibitors and masking agents such as diuretics.
Many of the same are repeated on the prohibited in-competition list with a few notable additions. Stimulants such as cocaine, methamphetamine, adrenaline, ephedrine and strychnine show up, as well as narcotics such as morphine, oxycodone, methadone and cannabinoids.
All in all, the code is very long and complex. So if athletes are looking for a chemical way to improve their performance without breaking any rules, they'd better practice their legalese as well as their sport.