South Sydney players will be used to trial hair follicle testing for prescription drugs as it emerged that neither Dylan Walker nor Aaron Gray had been prescribed one of the two painkillers the pair are believed to have overdosed on by the surgeons who operated on them last week.

A remorseful Walker and Gray were released from St Vincent's Hospital on Friday afternoon after being rushed to intensive care at 3.45am Tuesday following a suspected overdose from the use of painkillers, reported to be Targin, a tablet form of oxycodone, and Tramadol. With Walker (hand) and Gray (knee) both undergoing post-season operations last week, it was initially assumed they had taken the other's medication as well as their own but Fairfax Media understands that neither of the lifelong friends and teammates was prescribed Tramadol by their respective surgeons.

How the pair came to possess the medication is expected to form part of an investigation the Souths board have charged chief executive John Lee with heading up, but Rabbitohs officials also believe the NRL needs to widen its research into the use of prescription drugs in the game and have offered to make available their players for a trial of hair follicle testing.

"I can confirm that our chairman [Nick Pappas] and our coach Michael Maguire would like to be at the forefront of a new trial and that trial would be around a voluntary trial for testing for a prescribed medicines through the use of hair follicles," Lee told a press conference at St Vincent's Hospital. "It is something that takes place in other parts of the world and we think it's time there's greater monitoring as well as education so as this incident can be prevented."