King's Drug Control CentreSubstances or certain methods are banned for a number of reasons: they might confer upon an athlete an unfair competitive advantage; are poisonous or dangerous to health; or are illegal.
Broadly, these include stimulants like amphetamines, hormones and diuretics which mask other competitive-enhancing substances.
Some steroids like nandrolone mimic the effects of the male hormone testosterone in the body and help build up muscle bulk but over time can lead to damage to vital organs.
Other, banned, methods such as blood doping are designed to boost the rate of oxygen transfer vital in efficient muscle function. This technique involves attempting to increase the number of red blood cells in the body - normally by the reintroduction of an athlete's own stored blood cells back into his body prior to a competition.
More recently, gene modification - manipulating the genetic code to enhance performance - has emerged as a potential new problem.
Other chemicals such as narcotics and cannabinoids including heroin and cannabis, alcohol and beta-blockers are banned under certain circumstances, but like most substances on the banned list might have legitimate therapeutic or medicinal uses outside the world of sport.
In this exhibition