"It wasn't necessarily to take them socially or recreationally, they were just there to help with anxiety levels, travelling, all sort of stuff. Boys did end up relying on them a little bit too heavily sometimes."
The 36-year-old Koopu, who had a 10-year Warriors career, suggested something similar occurred at the Melbourne Storm, where he played in 2009.
"I heard of boys getting hooked on sleeping pills and that sort of thing, but not too much on painkillers," he said.
Koopu said players would have sleeping pill competitions.
"Every now and then the boys would have sleeping pills and then try to fight them to the death and not go to sleep. Of course that never ever worked, the boys just basically fell asleep," he said.
Manu Vatuvei, Ben Matulino, Bodene Thompson, Albert Vete and Sam Lisone admitted to the club they mixed prescription drugs and energy drinks on a night out following a big loss to the Storm. They were stood down for one NRL game and banned from international selection. Vatuvei is on indefinite medical leave while the others will be hoping for recalls to play against Penrith on Saturday.