Performance enhancing dope: Should sport ban cannabis?

The expulsion of an American judo player from the London 2012 Olympic Games on Monday after he tested positive for marijuana prompted scientists to question the sense behind the drug's inclusion on the World Anti Doping Agency's (WADA) banned list.

Few experts think marijuana, or cannabis - whether it's eaten or smoked - can do much to enhance the kind of speed, strength, power or precision that Olympic athletes strive for.

And many wonder whether the expensive time and effort of sporting drug testers might be better spent catching serious cheats who top up their blood with EPO or pop anabolic steroids to boost testosterone levels and muscle growth.

"There's no evidence cannabis is ever performance enhancing in sport, and since its use is legal in a number of countries, there's no reason for it to be banned by WADA," said David Nutt, a professor of neuropsychopharmacology at Imperial College London.

"I can't think of any sport in which it would be an advantage. And it seems ludicrous that someone could quite legally smoke cannabis in Amsterdam in the morning and then come over to London in the afternoon and be banned from competing."

What is cannabis?

Cannabis is a drug produced from the Cannabis sativa (commonly known as hemp) or Cannabis indica plant, which is related to nettles and hops. It's believed to have originated in the mountainous regions of India, and grows wild in many parts of the world.

The plant contains more than 400 chemicals, including cannabidiolic acid, an antibiotic with similar properties to penicillin. The different chemical derivatives of the plant can be used for medicinal or recreational purposes.

The recreational drug cannabis comes in many forms – herbal (dried plant material), resin, powder and oil - and is known by many slang terms, including weed, pot, grass and hash. In the UK, cannabis is a Class B illegal drug.

The heart of the problem is where to draw the line between performance enhancing drugs - which many experts agree should be prohibited in sport because they make the contest unfair - and recreational drugs like marijuana, which is unlikely to boost performance but could give sport a bad image.

SCIENTIFIC OR POLITICAL?

While it is generally accepted that cannabis is unlikely to give athletes any advantage in fast-paced sports, some experts say it could prove helpful in sports like shooting or golf where a steady hand is needed.

Under WADA's rules, athletes face a two-year ban if cannabis is found in their system while they are in competition.

But the anti-doping body does not sanction those who test positive for marijuana outside of competition times, while they are in training camps or during rest periods.