The report, published in the British Medical Journal, found World Health Organisation (WHO) guidelines on the use of medicine to treat the virus were prepared by experts who had received consulting fees from the top two manufacturers of the drugs - Roche and GlaxoSmithKline.
The WHO's decision to name the flu a "pandemic" is also coming under scrutiny from European investigators, and stands accused of exaggerating the dangers of the H1N1 outbreak, which emerged in April last year.
Laboratory tests have confirmed more than 18,000 deaths from H1N1 infection, according to WHO figures, but the virus has turned out to be less deadly than feared.
Also, symptoms suffered by most people infected with the virus have been mild.
'Exaggerated scare story'
A report by the Council of Europe, also released on Friday, accused the WHO of a lack of transparency over the pandemic announcement - saying it wasted huge sums of money and provoked "unjustified fears".
Paul Flynn, the author of the report, told Al Jazeera that the WHO warnings were "exaggeration on stilts".
"The WHO changed the definition of the most serious pandemic for one that would include the possibility of a tremendous amount of deaths to one that wouldn't include that severity ... and this is extraordinary.
"[The] announcement caused the world press to go into hysteria and tell people that we're going to see a plague like the 1918 one.
"There was never any scientific evidence to justify this exaggerated scare story.
"They frightened the world witless about this and caused this vast expense and disruption of health services," he said.
But Gregory Hartl, a WHO spokesman in Geneva, said the organisation does not believe any undue influence was exerted on its work.
"In April 2009, we knew very little about [this new virus] and our duty was a duty of care to save lives," he told Al Jazeera.
"So we were helping member states prepare for outcomes that were unknown at the time. We were lucky that afterwards the virus showed itself to be much milder than it was initially thought it could have been.
"Remember what would have happened had WHO and the world done nothing, and it turned out to be a virus on the scale of mortality of bird flu."
The WHO initially urged rapid development of treatments and vaccines, fearing the virus had the potential to kill millions.
As a result wealthy countries spent billions on medicines which many believe are now unnecessary.
Across Europe, governments are now trying to resell their stockpiles of swine flu vaccine.
An emergency committee of the WHO has been waiting for signs of how the virus is developing in the southern hemisphere winter before making a full pronouncement on its state.
|WHO have confirmed more than 18,000 deaths from H1N1 infection [GALLO/GETTY]
The committee, composed of 15 external advisers, believes it is critical for countries to maintain vigilance concerning the pandemic, including necessary public-health measures for disease control and surveillance, Margaret Chan, the WHO director-general, has said in a statement.
Chan said that pandemic flu activity was expected to continue, and the committee would meet again by mid-July to review the status of the outbreak once more data from the winter influenza season in the southern hemisphere was available.
The panel met on Tuesday, but Chan delayed any announcement until Thursday as the committee, whose members were spread around the world for the meeting by teleconference, put the final touches to the wording of their recommendation.
Chan's decision, based on the committee's recommendation, means that the outbreak, widely known as swine flu, remains at phase six on the WHO's pandemic scale, which has been at the top level of six since June 2009.
WHO experts say the virus remains a threat to some vulnerable people, notably pregnant women, young children and those with respiratory problems, and such groups would continue to need vaccinations.
Fiona Godlee, the editor-in-chief of the British Medical Journal (BMJ), told Al Jazeera the findings were "not surprising" but that the public should be "shocked by this".
"This was a major decision that affected governments around the world, vast sums of public money and private profit, and we need to really understand exactly the extent to which WHO's advice was influenced by the pharmaceutical industry," she said.
"The investigation by the BMJ suggests that there was substantial influence at a number of key stages in the declaration of the pandemic, the definition of the pandemic, the triggering of vaccine contracts around the world and advice to government to stockpile large numbers of expensive antiviral drugs.
"The extent of misjudgment was really very profound in this case."
But WHO experts maintain that the HIN1 virus could spread easily among people if it were to mutate into a more dangerous or lethal form.
The virus is currently most active in parts of the Caribbean and Southeast Asia, and activity in Africa is low or sporadic.
Source: Al Jazeera and agencies