The NRL will this year begin testing for prescription drugs as the Warriors' club doctor said he believes many players are mixing sleeping pills with alcohol and energy drinks.
John Mayhew, the doctor for New Zealand's NRL side the Warriors, told ABC TV's 7.30 on Tuesday night that having spoken with players and other club medicos, "cocktailing" is widespread.
"Basically they get a high and it doesn't contravene any of the existing drug testing protocols," Dr Mayhew told 7.30.
"Widespread is the word I'd use."
Mayhew also believes the problem exists in other football codes.
His comments came just before the NRL announced on Wednesday they would start testing for prescription drugs, including the controversial sleeping pill Stilnox.
The NRL's chief operating officer, Jim Doyle, concedes there's anecdotal evidence that prescription drugs are being abused by players but no sanctions will be imposed in 2014 for those that test positive.
The NRL reached agreement with the Rugby League Players Association to test players for two classes of prescription drugs: benzodiazepines (which include brand names such as Valium, Serepax, Mogadon and Rohypnol) and zolpidems (which include Stilnox, Zolsan and Stilnoct).
"During the 2014 season, we will conduct testing for data-gathering purposes only," Doyle said in a statement.
"We want to find out if we do have a problem with prescription drugs in rugby league because, at present, there is only anecdotal evidence."
If a player tests positive this year, the NRL will set up a confidential meeting between the player, his club doctor and the NRL's chief medical officer to determine why the player is taking the drug and whether he needs counselling or rehabilitation.
However, if the testing regime shows there's a serious issue with the use of prescription drugs, Doyle said sanctions may be imposed in 2015.
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