Performance-enhancing drugs (also known as PED) are substances used by athletes to improve their performances. The term may also refer to drugs used by military personnel to enhance combat performance. Although the phrase performance-enhancing drugs is popularly used in reference to anabolic steroids or their precursors (hence the colloquial term "steroids"), world anti-doping organizations apply the term broadly.
Diuretics expel water from the body. They are often used by athletes who need to meet weight restrictions, such as wrestlers. Many stimulants also have a secondary diuretic effect and are also used as masking drugs.
Blood boosters increase the oxygen-carrying capacity of blood beyond the individual's natural capacity. They are used in endurance sports like cycling and Nordic skiing. EPO is one of the most widely-known drugs in this class.
Masking drugs, as a group, do not have any specific type of pharmacodynamic action; a masking drug is simply any drug used to prevent the detection of other classes of drugs. The chemical compositions and administration regimens of masking drugs change as quickly as testing methods do. A common example of a masking drug is epitestosterone, which possesses no performance-enhancing effects, but restores the testosterone/epitestosterone ratio (a common criterion in steroid testing) to normal levels after anabolic steroid supplementation.
The classifications of substances as performance-enhancing drugs are not entirely clear-cut and objective. As in other types of categorization, certain prototype performance enhancers are universally classified as such (like anabolic steroids), whereas other substances (like vitamins and protein supplements) are virtually never classified as performance enhancers despite their effects on athletes' performance. This is because athletes can get the correct amount of protein and supplements their body needs by having a proper diet As is usual with categorization, there are borderline cases; caffeine, for example, is considered a performance enhancer by some athletic authorities but not others.