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Performance-enhancing drugs 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.
Types of performance-enhancing drugs 
The phrase has been used to refer to several distinct classes of drugs:
- Lean mass builders drive or amplify the growth of muscle and lean body mass; sometimes they're used to reduce body fat. They can also reduce the time it takes an athlete to recover from an injury. This class of drugs includes anabolic steroids, xenoandrogens, beta-2 agonists, selective androgen receptor modulators (SARMs), and various human hormones, most notably human growth hormone, as well as some of their precursors. Performance-enhancing drugs are also found in animals as synthetic growth hormone.
- Stimulants stimulate the body and mind to perform optimally by enhancing focus, energy, and aggression. Some examples are caffeine, amphetamine, and methamphetamine.
- Painkillers mask athletes' pain so they can continue to compete and perform beyond their usual pain thresholds. Blood pressure is increased causing the cells in the muscles to be better supplied with vital oxygen. Painkillers used by athletes range from common over-the-counter medicines such as NSAIDs (such as ibuprofen) to powerful prescription narcotics.
- Sedatives are sometimes used by athletes in sports like archery which require steady hands and accurate aim, and also by athletes attempting to overcome excessive nervousness or discomfort. Alcohol, diazepam, propranolol, and marijuana are examples.
- Diuretics expel water from athletes' bodies. They are often used by athletes such as wrestlers, who need to meet weight restrictions. Many stimulants also have secondary diuretic effect. (Also used as a masking drug)
- Blood boosters increase the oxygen-carrying capacity of blood beyond the individual's natural capacity. Their misuse is centered on endurance sports like cycling and nordic skiing. EPO is the most publicly known drug in this class.
- Masking drugs are used to prevent the detection of other classes of drugs. These evolve as quickly as do testing methods – which is very quick indeed – although a time-tested classic example is the use of epitestosterone, a drug with no performance-enhancing effects, to restore 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.
See also 
- Anabolic steroid
- Banned substances in baseball in the United States
- Blood doping
- Ergogenic aid
- Ergogenic use of anabolic steroids
- Steroid use in American football
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