James Magnussen and his teammates from the Australian men's 4x100m freestyle relay squad have admitted using a sedative banned by their national Olympic committee in a bonding session before the London Games.

The prescription drug Stilnox was banned by the Australian Olympic Committee just before the 2012 Games and the athletes now face sanctions from the governing body for breaching their Olympic team membership agreement.

Stilnox, a brand of the medication zolpidem, is not banned by the World Anti-Doping Agency but was prohibited by the AOC because of its hallucinatory effects and after former Olympic champion Grant Hackett said he had become addicted to it.