Magnus Carlsen, the Norwegian world champion, and his Russian challenger, Sergey Karjakin, were tested during their title match last November.

Fide, the world governing body, adopted a drug policy in 1999 after it became a member of the International Olympic Committee, because the IOC requires members to be a signatory to the World Anti-Doping Agency.

As they were already on the Wada banned list, ritalin and modafinil were automatically prohibited while caffeine use was restricted.

However, so far no one is known to have tested positive.

The game's only brush with a doping scandal to date was a curious incident involving the top Ukrainian Grandmaster Vassily Ivanchuk who refused to provide a urine sample at the Chess Olympiad in 2008.

The "scandal" ended up fizzling out when it emerged Ivanchuk, the current world rapid chess champion, had just been so annoyed at losing he fell out with the official.

Dr Klaus Lieb, a professor of psychiatry and psychotherapy at the University of Mainz, in Germany, said: "There is lots of data showing that a subject in a sleep-deficient state or exhausted people do profit from an enhancer.

"We recommend to introduce rigorous doping controls in chess competitions."