The Akarana Falcons will be without prop Siliga Kepaoa for the upcoming National Premiership season following two positive tests for the prohibited substance Higenamine.
The Falcons have won consecutive New Zealand Rugby League National Premiership titles, with Kepaoa scoring the opening try in last year's grand final win over Waikato.
But he won't be available for the Falcon's title defence, following his transgression.
Kepaoa's first positive test was after a Falcons training session on 19 September 2017.
Because Mr Kepaoa was not notified of the first positive result before his second test, the two violations are treated as one, in accordance with the Sports Anti-Doping Rules.
The Sports Tribunal of New Zealand has imposed an 18-month ban backdated to 19 September 2017.
On the doping control form on both occasions Kepaoa listed that he used the product "Oxyshred", which advertises itself as a 'super potent thermogenic fat burner'.
Oxyshred is a weight loss product and does not claim to boost performance, but higenamine is a listed ingredient in Oxyshred
Kepaoa said he relied on the salesperson's advice at the North Shore retail shop where he purchased the supplement, who told him it was safe, after he had explained he would be subject to testing as a member of the Falcons.
Kepaoa acknowledged he should have checked the product for himself.
Drug Free Sport New Zealand chief executive Nick Paterson said despite Mr Kepaoa receiving anti-doping education around the risks of using supplements, the 29-year old didn't take the threat of ingesting a prohibited substance seriously.
"In Mr Kepaoa's case the prohibited substance Higenamine was actually listed on the label of ingredients on the back of the supplement container," said Paterson.
"As a top-level amateur athlete who has had education about the risk of taking supplements it's disappointing that once again, a talented sportsman is going to be on the sidelines. These sanctions are preventable with a bit of research and checks through the right channels."
It is the second sanction handed down within a few weeks for the same substance, Higenamine.