Scientists have called for a crackdown on doping in chess after it emerged players may be taking performance-enhancing substances.
A major study has for the first time identified two stimulants that significantly boost a player's endurance and ability to concentrate during a match.
Meanwhile, researchers have contacted 1,500 strong players to ask about the prevalence of drug use in the game.
Researchers are yet to reveal the findings of the survey, but say they now have some idea of how much the two drugs are used by the chess-playing community.
The main study, published in a leading journal, was carried out by 13 professors and researchers from several German universities and the University of Stockholm, who analysed more than 3,000 games played by 40 players.
Among its findings were that modafinil, a drug used used for treatment of disorders such as narcolepsy, improved the players' performances by an average of 15 per cent.
Methylphenidate, more commonly known as the ADHD treatment ritalin, boosted performances by 13 per cent, and caffeine, which they also tested, by around 9 per cent.
The study was carried out by giving each player a series of neuropsychological tests and questionnaires and then asking them to play against computers running the formidable chess-playing program Fritz 12.
One surprising finding was that the drugs made the subjects play slower, suggesting that rather than enhancing decision-making, drugs improved players' ability to spend more time on a decision and perform more thorough calculations.
The authors wrote: "This suggests that neuroenhancers do not enhance the quality of thinking and decision-making per time unit but improve the players' ability or willingness to spend more time on a decision and hence to perform more thorough calculations."
Drug-testing to some exists to some extend in chess, but only at prestige events like the world championship.
Magnus Carlsen, the Norwegian world champion, and his Russian challenger Sergey Karjakin were both tested during their title match last November.
Fide, the world governing body, first adopted a drug policy in 1999 after it became a member of the International Olympic Committee, and was required to become a signatory of WADA.
It did so not because it thought there was a problem, although chess players were previously known to drink gallons of coffee during matches, but because the IOC requires members to be a signatory to the World Anti-Doping Agency. That meant testing.
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 and some top players have refused to accept drug taking in the cerebral game could enhance performance.
Indeed, so far the game's only brush with a doping scandal 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, a notoriously grouchy character, 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 that the researchers wanted to see whether people who already were performing at a high level mentally could have their performance enhanced through chemicals.
"There is lots of data showing that a subject in a sleep-deficient state or exhausted people do profit from an enhancer," Dr Lieb said.
"We were really interested to show whether it is possible to show an enhancement effect, or a hyper performance effect in subjects who already perform at the top level of their cognitive performance."
In their games, the players had 15 minutes total for their moves, the computers had six. Before each set of 10 games, the players were given either methylphenidate, modafinil, caffeine, or a placebo.
Dr Lieb said the researchers went into the study, published in European Neuropsychopharmacology, with the expectation that the stimulants would not show much benefit.
"We primarily thought that it is not possible to enhance high cognitive tasks and were astonished to find such results," he said.
Dr Lieb cautioned that while the drugs seem to boost performance, taking them was not a good idea. "Their use may cause severe side effects and dependency, especially with repeated use," he said.
Dr Lieb was clear on one effect he thought the research should have. He said: "We recommend to introduce rigorous doping controls in chess competitions."
Fide has been approached for comment, but is yet to respond.
However, in its anti-doping policy the federation states: "The notion of 'cognitive enhancing' drugs has gained periodic attention and it is clear that such pharmacology has the potential to be of benefit in chess, an essentially cognitive sport. Modafinil, Adderall and Ritalin are potentially implicated."