On Monday, RNZ revealed officials told Costello that Philip Morris - the "sole supplier" of HTPs in New Zealand, would be the only commercial beneficiary of the tobacco tax cuts.
Costello announced the cut on excise tax on HTPs in July saying she aimed to make them more attractive as an alternative to smoking.
Treasury said there was clear evidence that HTPs were more harmful than vaping, but Costello said she had independent advice supporting the move.
RNZ asked where the "independent advice" came from, but Costello would not say.
Luxon told RNZ's Morning Report he had not seen the independent advice.
However he said the government was committed to trying anything that would stop people smoking tobacco.
"It's simple as, we've got a smokefree target... vaping has helped get people off cigarettes
"(HTPs are) potentially less harmful than smoking and we will try anything to get New Zealanders off smoking."
The use of HTPs was a 12 month trial after which it would continue if successful, or be cut if not, Luxon said.
"The reality is we'll see how it goes... what we're focused on is the big picture which is making sure people come off smoking, that's what this is all about.
"We're going to try all of the alternatives and this is one of them."
Luxon said ministers received a range of advice and while he hadn't see this specific piece he had confidence in Costello.
"I have every confidence in the minister."
She, like the government, was committed to lowering smoking rates in New Zealand, he said.
Costello was reprimanded by the Chief Ombudsman last month for her handling of a mystery document containing tobacco-industry friendly ideas, which she passed to health officials to develop policy.
In a statement to RNZ, Costello has denied having received advice from the tobacco industry.
