Passage: Performance-enhancing substances, also known as performance-enhancing drugs (PED), are substances that are used to improve any form of activity performance in humans. A well-known example involves doping in sport, where banned physical performance -- enhancing drugs are used by athletes and bodybuilders. Athletic performance-enhancing substances are sometimes referred to as ergogenic aids. Cognitive performance-enhancing drugs, commonly called nootropics, are sometimes used by students to improve academic performance. Performance-enhancing substances are also used by military personnel to enhance combat performance.\n\nQuestion: Based on this passage, what is the definition of performance enhancing drugs?
Let’s work this out in a step by step way to be sure we have the right answer.
substances that are used to improve any form of activity performance in humans
This is the relevant information: Performance-enhancing substances, also known as performance-enhancing drugs (PED), are substances that are used to improve any form of activity performance in humans.

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Thus, the answer is substances that are used to improve any form of activity performance in humans