“The problem is the elite athletes should be seen as role models for young kids, and so they ban cannabis because they don’t want to have the image of gold medalists smoking joints,” said one British-based sports scientist who asked not to be identified because of the sensitivity of the issue.

A photo of the American swimming champion Michael Phelps inhaling from a glass pipe used for smoking marijuana in 2009 sparked criticism from the U.S. Olympic Committee.

In a statement released shortly after the picture was published by a British tabloid newspaper, Phelps admitted to smoking pot and apologized for what he described as “bad judgment”. He did not receive a doping ban because it was not “in competition”.

Experts say that row, as well as Monday’s ruling on American judoka Nick Delpopolo - who said he inadvertently ate the drug in a marijuana brownie - is far more to do with the image of sport than any form of cheating.

“It’s hard to imagine how smoking a joint or eating marijuana brownies is going to help somebody in judo,” said Michael Joyner, a member of the Physiological Society and a researcher at the Mayo Clinic in Minnesota in the United States.

“My advice to WADA is that they should focus on drugs that are clearly performance enhancing in the sports where they are clearly performance enhancing.”

SENSITIVE ISSUE

Some national sporting bodies are also kicking back against WADA’s stance.

Australia’s Coalition of Major Professional and Participation Sports called in May for marijuana to be removed from the list saying it was wrong to group it with performance enhancing drugs like human growth hormone and steroids.

Substances on WADA’s banned list should meet two of the following criteria: they are proven to be performance enhancing, they are dangerous to the health of athletes, or they are contrary to the spirit of sport.

While there are few signs that marijuana can enhance sporting performance, there is evidence to suggest it could have a negative impact.

Studies have shown that THC - the ingredient in cannabis that induces the “high” - increases blood pressure and heart rate while also decreasing cardiac stroke volume, leading to diminished peak performance.

It can also slow reaction times, cause problems with coordination, reduce hand-eye coordination, and interfere with visual perception.

Anti-doping authorities were not keen to discuss the issue on Monday.

Officials at UK Anti-Doping declined to comment, and when Reuters sent emails to WADA’s media relations office asking for a statement on why cannabis is banned, WADA responded by saying it was too busy to provide a comment on Monday.

WADA president John Fahey indicated in May the agency may look at changing the criteria for cannabis as a banned substance for athletes, but no decision is expected this year.

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By Kate Kelland