The area in which drugs are used most to enhance performance is in sports and specifically only those that involve inordinate amounts of strength, speed or endurance. There is no doubt that ingestion of small amounts of some drugs prior to performance can produce better results, or taken over a period of time during preparation can lead to a higher performing physique. The problem, however, is that over a number of years, the results of such substance intake can be a dramatic loss of health and early death. For this reason drug taking in sports is illegal: because of what it does to the body. We do not want to encourage young people to do things to their bodies that will lead them to an early death, no matter how much glory they bring us through their feats of drug induced achievement.
Musicians have been known to take drugs to enhance their performance and more than one actor has gone on stage drunk. Unlike in sport there is little argument over the merits of drugs in performance and it is usually seen as a liability.
Many drugs commonly taken, merely substitute for something that the body itself makes, such as nicotine. Other drugs introduce alien substances that stimulate or sedate depending on their active ingredient. The body is capable of manufacturing what stimulants, sedatives, hormones, drugs etc. that it needs from the food that we ingest. It is fun or medically prudent from time to time to ingest ready made drugs to complement our bodily functions, but the body has its own balance and when healthy and complete, is capable of producing what is needed when it is needed. Exceptions occur when a part of the body stops functioning and regular medication has to be taken, which happens to people increasingly as they get older.
Taking drugs does not change the level of functionality, it only uses the current level differently to produce different results. In order to excell the individual already has to be highly functional.
Further, using drugs may prevent the development of further functionality. Drugs produce short term results. Side effects and other distractions may temporarily hinder further development.