The NZRL stopped short of blaming the use of prescription drugs and energy drinks for the Kiwis' heavy defeat to Australia in last year's World Cup final but said it divided the group and saw management warn several players over their misuse.
The NZRL today released a statement around their findings into an investigation into last year's World Cup campaign at the same time as confirming Stephen Kearney as Kiwis coach for another two years.
Kearney has been reappointed until the end of the 2015, with a right of renewal through to the next World Cup jointly hosted by Australia and New Zealand in 2017.
"Stephen was the strongest candidate and presented his vision for the Kiwis strongly and passionately,'' NZRL chief executive Phil Holden said. "He really impressed the panel and demonstrated that he was the right man for the job.
"We've invested heavily in Stephen's development at this level and, generally, we feel he's elevated the programme significantly since taking over.
"We expect him to continue that progress and a two-year term will give us a chance to see how we're tracking towards the next tournament, while also allowing us to put some focused resource and support around him to ensure that he succeeds.
"This process has helped identify some future candidates in succession planning, and helped Stephen to really look hard at his own performance and how he can improve that going forward.''
Under Kearney's watch, the Kiwis won the 2008 World Cup and the 2010 Four Nations, but were outclassed by Australia in last year's final at Manchester, going down 34-2.
After reviewing the campaign, the NZRL stopped short of blaming the misuse of prescription medication for that defeat.
During the campaign, management warned several players for mixing sleeping pills and energy drinks as a recovery practice in a manner that had left some unable to function at 100 per cent afterwards.
"We're very concerned at the health risks involved in this practice and the players involved probably aren't even aware of the risk they are putting themselves at,'' Holden said. "Their behaviour certainly divided the group and, in some cases, probably affected how individual players recovered from games, so it was definitely a factor.
"But we can't in, all honesty, say it cost us the World Cup title. That would be disrespectful to an Australian side that deserve to rank among the all-time greats.''
While the medication/energy drink combination is neither illegal nor banned by Wada, this incident has galvanised rugby league's governing bodies on both sides of the Tasman in a drive to stamp out the practice.
The NRL has set up a taskforce on the issue, with NZRL represented by high performance manager Tony Iro. Clubs are now considering greater controls over the issue of sleeping pills to players.
"We've been heartened by the NRL's response to this, since our players operate in that environment for most of the year and any change can only be achieved through co-operation with their clubs,'' says Holden.
The NZRL review pinpointed several courses of action that need to be addressed, including: Maintaining player focus over a long campaign after an already lengthy NRL season, developing leadership depth to cover the loss of key senior players, reviewing and tightening the players' employment contracts to reflect NZRL expectations and the consequences for breaching those standards, maintaining consistent selection policy that reflects team culture, on and off the field and consolidating staffing structure.
New Zealand's next international fixture is the annual Anzac test against Australia at Allianz Stadium, Sydney on May 2.