The New Zealand Rugby Union has confirmed two leading All Blacks misused sleeping pills during the 2011 Rugby World Cup.
Cory Jane and Israel Dagg mixed the prescription drugs with alcohol, three days before the All Blacks' quarter-final against Argentina.
The combination can produce an amphetamine-like high.
NZRU chief executive Steve Tew says Cory Jane and Israel Dagg were reprimanded internally at the time.
He says there was no further investigation into possible misuse of sleeping pills as he believed it to be an isolated incident.
Tew says he only became aware of wider problems following the revelation rugby league players engaged in similar practices at last year's World Cup.
However, Tew says the rugby union won't follow league and implement testing for prescription drugs.
He says with games in different time zones, some players need help getting enough sleep and sleeping pills are an important part of player management.