Doctors are accepting thousands of dollars in gifts and travel from drug companies, ONE News has revealed.
Some district health boards say they have nothing to hide and others say they keep no record of what their staff have received.
The Government buys medicines through its drug agency, Pharmac. But it is doctors who decide which drugs to prescribe and in what quantities.
ONE News has discovered some doctors are receiving gifts, travel and even cash from drug manufacturers.
Some of the places visited by public sector health workers are Honolulu, Taiwan, Singapore and France, their travel costs paid by commercial drug giants.
"All of those gifts came with a price," said Associate Professor David Menkes of Waikato Clinical School.
A third of DHBs say their staff have received benefits.
Some have had their travel bills paid, allowing them to go to conferences.
Doctors are accepting fees to give speeches and lectures.
Some DHBs have even accepted cash "donations" from drug companies.
The practice is common, according to Menkes, who now turns those companies away.
"It became clear after a couple of years of being wined and dined that in fact I was being targeted for my usefulness to them," he said.
The two DHBs which have accepted the greatest amounts are Capital and Coast and Counties Manukau.
Neither would give ONE News an interview, but said they expect the receipt of goods and services to benefit patients.
They have policies preventing personal benefit and undue influence.
Medical Council chair Dr John Adams said research shows that
even when people don't think they are being influenced "by some of these relatively simple things", they are being influenced.
Menkes said: "Our clinical decision making is affected. We often make worse prescribing decisions and certainly more costly prescribing decisions."
The medical council says drug companies help doctors access useful training and development.
"Any doctor involved in these kinds of activities needs to be open and transparent in disclosing about it," Adams said.
But six DHBs could not tell ONE News what their staff had received because they don't keep records of it.
Julie Radford-Poupard of Women's Health Action said: Even the perception of that is really problematic. And I think it really undermines the trust and confidence of the general public."
Health Minister Tony Ryall says he expects doctors and nurses to abide by the codes of conduct that they have signed.
The Minister will now ask DHBs to standardise their reporting of gifts, travel and hospitality. That will force some DHBs to keep better records and be more upfront with the public about their links with drug companies.