The Consumers International lobby group accused drugmakers of using the methods to get doctors to prescribe products and persuade consumers they need them.
It said there was a "shocking" lack of publicity about where the $60bn (£33bn) annual marketing spend went.
Drug firms say that they act within strict guidelines.
The Association of the British Pharmaceutical Industry (ABPI) told the BBC News website that for UK-based firms there was "a stringent and transparent code of practice that goes beyond the requirements of UK law and the industry regulator".
Consumers International said it had analysed the selling techniques of many leading companies, including Bayer, GlaxoSmithKline and Johnson & Johnson.
Richard Lloyd, the group's director general, said: "The pharmaceutical industry spends nearly twice as much on marketing as it does on research and development, yet consumers know next to nothing about where this money is going."
He called for a revision of marketing regulations to achieve "more transparency from drug companies".
In most Western markets direct advertising to consumers is banned.
But Mr Lloyd said there were other methods drug companies were using to influence opinion.
These include the sponsoring of patient lobby groups, funding disease awareness campaigns and use of hospitality packages for medical experts.
The report cites sponsorships by such firms as Eli Lilly and Pfizer. The latter, the maker of Viagra, sponsored a campaign by the Impotence Association which sported the Pfizer logo.
The report said only one of the firms studied, Orion Pharma, provided specific marketing budget information.
It also pointed to the "large numbers of serious, recent and repeated breaches of marketing codes".
This showed the "current regulatory framework is clearly insufficient to prevent systemic violations of marketing regulations".
However, the ABPI said the number of complaints raised showed the system, which had been strengthened this year, was working.
It said complaints from drug companies about fellow firms' activities showed the self-regulation was effective.
But it also said it was vital for doctors to know about products.
"There is no point having innovative new medicines if they remain unused," an association spokesman said.
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