Drug companies use unscrupulous and unethical marketing tactics not only to influence doctors to prescribe their products but also subtly to persuade consumers that they need them, a report claims today.

Consumers should be concerned because time and again the companies violate their own industry's ethical marketing codes. Patients' health may suffer if a drug like Vioxx - a painkiller later withdrawn - is over-promoted. Yet, says Consumers International, which has compiled the report, there is "a shocking lack of publicly available information about the $60bn [£33bn] spent annually by the industry on drug promotion".

The report examines the marketing practices of 20 of the world's biggest drug companies. It alleges that:

· Drug companies are promoting their products through patients groups, students and internet chatrooms to bypass the ban on advertising except to doctors.

· They offer information to the public on "modern" lifestyle diseases, such as stress and poor eating habits, to encourage people to ask their doctors for medicines.

· They make inaccurate claims about the safety and efficacy of their drugs.

· Doctors are offered incentives to prescribe and promote drugs including kickbacks, gifts, free samples and consulting agreements.

· Many companies have been implicated in anti-competitive strategies, including cartels and price hikes.

Drug companies are not permitted to advertise products to the public. But companies are increasingly looking to influence consumers directly through funding patient groups and launching "disease awareness campaigns", which do not name a product but are likely to encourage patients to seek treatment.

"This type of 'nice-and-friendly' marketing is often disguised as corporate social responsibility and has been shown to create a subtle need among consumers to demand drugs for the conditions, while giving consumers a sense of trust in the pharmaceutical companies," says Consumers International.

Pfizer sponsored a campaign by the Impotence Association which bore the company logo. The UK prescription medicines code of practice authority - part of the Association of the British Pharmaceutical Industry (ABPI) - ruled that this was inappropriate because it could encourage patients to ask doctors for Viagra, a Pfizer product, by name.

Eli Lilly, which has a rival drug, is currently sponsoring a TV advertising campaign in the UK for a website called Love Life Matters, which urges women whose husbands have an erection problem to see their doctor. The website bears the company logo and a downloadable booklet clearly spells out the Lilly sponsorship.

In the US, where advertising to consumers is allowed, a still more subtle tactic has been employed. In 2002, Lauren Bacall, being interviewed on NBC's Today programme, told an anecdote about a friend who had gone blind from macular degeneration and mentioned a new drug for the condition made by Novartis - without disclosing she had been paid by the company for her appearance.

The Consumers International report, called Branding the Cure, reveals a novel tactic by Wyeth. Its website offers women what it calls a "social service" - a regular text message to remind them to take their contraceptive pill. But to get the service, they need a special code from their doctor, which is only available to those taking Wyeth's brand.

All the companies say they have internal codes of practice in line with industry principles on ethical marketing. Most say they have tightened them following rulings against them by regulatory bodies.

Best placed to persuade doctors of the merits of a new drug are other doctors. Drug companies often pay specialised medical communication agencies to recruit and train leading doctors, specialists and academics as "key opinion leaders", or KOLs, as they are known in the business. These people will be paid to promote drugs to other doctors through presentations, research papers, discussions and debates.

"The relationship between companies and KOLs is not explicitly transparent," says the report. "As a consequence, consumers and patients, and in some cases health professionals, may not always be aware how motivation for individual profit could play into the drug information they receive via the KOLs."

Studies have shown that the published results of drug trials are more likely to be positive where the funding is provided by the manufacturer. Many research articles are ghostwritten in the name of eminent doctors who may or may not have had access to all the relevant study data.

"All the while, consumers are in the dark about how their medicine consumption choices are the result of veiled relationships between doctors and the pharmaceutical companies," says the report. "We believe that doctors should have their patients' interests as a priority rather than personal profit."

Violations of industry-wide drug promotion codes occur with regular fre-quency, says the report. The 20 companies were involved in 972 breaches of the ABPI's rules on ethical drug practices between 2002 and 2005. More than 35% of those breaches, the largest category, had to do with misleading drug information.

More than half of the 20 companies whose marketing practices are examined in the report have been implicated in controversies regarding free samples, kickbacks and gifts to medical professionals, it says. Half have breached the ABPI code of practice on the conduct of the medical representatives who visit doctors.

Most of them - 17 out of 20 - have been involved in publicising irresponsible or controversial promotional materials. Only two companies, GSK and Novartis, are transparent in reporting the number of confirmed breaches of marketing codes and any sanctions imposed.

This record raises questions about the efficacy of self-regulation. "The sheer volume of reported breaches indicates that even the companies with apparently the most comprehensive compliance programmes are not fully effective in preventing breaches of marketing codes. This problem extends to the biggest companies, such as GSK and Pfizer," says the report.

The ABPI says that the large number of cases brought under the code shows that self-regulation is effective.

"We think it shows that it is working," said its spokesman, Richard Ley. "We are pleased that so many reports or complaints made under the code are by one company against another. It shows how determined a company is not to let another one get away with it."

Its code of practice has been strengthened this year and widened to encompass dealings with patient groups. Companies will have to declare which ones they sponsor, although they do not have to say how much money they give them.

Mr Ley said they did not know whether there would be more or fewer complaints following the changes.

"It may be that we get a huge increase because it is even more stringent than the old one. On the other hand, there has been renewed commitment by the companies to it and it may not make a big difference."