Study finds lack of supporting evidence to validate claims made by health firms.

Some drug advertisement claims pitched at New Zealand doctors offer no supporting evidence, a new study warns.

A study in today's New Zealand Medical Journal says a "high proportion of advertisements failed to meet New Zealand regulatory requirements that claims are valid and have been substantiated".

The study looked at advertisements in the New Zealand Doctor and Pharmacy Today from July 2013 to June 2014.

Of the 290 claims made, 33 per cent cited no supporting evidence and 35 per cent cited one or more random controlled trials (RCT).

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Senior author Dr Lianne Parkin said such trials were the best way to test the effectiveness of drug treatments, though the research found 78 per cent of the trials were industry-funded and only 8 per cent of RCT-backed claims were supported by evidence with a low risk of bias.

Dr Parkin said many practising doctors and pharmacists were unlikely to have the time and resources to locate and check the original source material cited in pharmaceutical advertisements.

"Our overall findings are consistent with concerns internationally that the therapeutic claims made in some advertisements are not supported by good evidence and might have a negative impact on what doctors prescribe."

However, both New Zealand Doctor and Pharmacy Today said all their advertisements went through the Therapeutic Advertising Prevetting System (TAPS).

New Zealand Doctor editor Barbara Fountain said the company had relied on TAPS vetting.

"We will definitely be having a look at it now," she said. "But I am confident that GPs aren't relying solely on advertising."

Pharmacy Today editor Jodi Yeats also planned to talk to TAPS.

She said all the drugs would have gone through an approval process before being put on the market.

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Lindsay Mouat, chief executive of the Association of New Zealand Advertisers, which administers TAPS, said the Advertising Standards Authority's code for advertising therapeutics stipulated the need to substantiate all health claims.

RCTs were not the only way to prove drug company claims were accurate, he said.