Vital data on prescription medicines found in millions of British homes has been suppressed by the powerful US drug regulators, even though the information could potentially save lives.

An investigation by The Independent on Sunday shows that, under pressure from the pharmaceutical industry, the American Food and Drug Administration routinely conceals information it considers commercially sensitive, leaving medical specialists unable to assess the true risks.

One team of investigators found that 28 pages of data had been removed from the FDA files on one of a new family of painkillers because of confidentiality.

Last week a major research study led by Professor Julia Hippisley-Cox at Nottingham University, revealed that ibuprofen, the supposedly "safe" painkiller, increases the risk of heart attack by almost a quarter. The finding was a particular blow to thousands of users who have already switched from the best-selling drug Vioxx, which was withdrawn last year after evidence that it too could increase the risk of heart attacks.

Key information about Vioxx and other drugs that form part of the new generation of painkillers called Cox-2 inhibitors had been suppressed, it emerged. Now researchers are questioning the reliability of the data about other drugs, including the full range of painkillers.

Dr Peter Juni, one of the team of Swiss investigators who helped to expose the risk of the new-generation drugs, claims his efforts were obstructed by the FDA.

"As part of the Freedom of Information Act, the agency is required to make available its reports on all drugs that are approved. Unfortunately, these reports are not as useful as they could be,'' he and his team say in an editorial in the British Medical Journal.

"For example, only 16 out of at least 27 trials of celecoxib that were performed up to 2002 in patients with musculoskeletal pain were included in the relevant reports... In the case of valdecoxib, we found that many pages and paragraphs had been deleted because they contained trade secret and/or confidential information that is not disclosable.''

Dr Juni, senior research fellow in clinical epidemiology at the University of Berne, is demanding that drug companies be legally required to make public any adverse effects as soon as they become available. Researchers also want more independent research, with financial firewalls between drug companies and doctors carrying out clinical trials.

Last year The Lancet published trial results that showed that unacceptable heart risks linked to the drug rofecoxib (sold as Vioxx) were evident four years before it was finally withdrawn by its maker.

The Lancet's editor, Richard Horton, said at the time that the discovery pointed to lethal weaknesses in the FDA's approach. He said: "Too often the FDA saw and continues to see the pharmaceutical industry as its customers, a vital source of funding for its activities, and not as a sector of society in need of strong regulation."

It emerged that FDA supervisors had attempted to suppress a report by Dr David Graham, associate director of the FDA's own Office of Drug Safety, showing that patients taking Vioxx suffered five times as many heart attacks as patients taking another pain reliever, naproxen.

Dr Graham's supervisors refused to allow him to present his conclusions at a meeting in France and later sought to interfere with the publication of his study results when they were scheduled to appear in The Lancet. Merck, the drugs company behind Vioxx, subsequently acknowledged the risk of heart attacks, and the article was published.

Speaking yesterday, Dr Juni said: "In some instances we had great difficulty in disentangling data. Not all the trials were reported, and it was difficult to see which results went with which trial. In some cases it took my group more than 1,000 hours to disentangle the information. We say that safety data from trials should be made available publicly."

The older drugs involved - ibuprofen, naproxen and diclofenac - have been around for so long that all are out of patent. Some earlier studies have suggested that they increase heart attack risks but this has been overlooked because they cause the more serious side effects of bleeding in the stomach or the development of ulcers.

The FDA has also run into trouble over antidepressants. Internal memos and a secret government report showing an increased incidence of suicide among children taking antidepressants surfaced in July last year. The report, by Dr Andrew Mosholder, an expert at the FDA's Office of Drug Safety, presented an analysis of 22 studies of 4,250 children on nine different antidepressants, and found that their risk of "suicide-related events" was twice that of children given a placebo. But that information was suppressed by the agency. After the report was leaked, Dr Robert Temple, formerly the associate director of medical policy at the FDA's drug evaluation centre, defended the FDA's actions saying the results were "prem-ature". The agency is investigating the leaking of the report.

In later reviews, Dr Mosholder's findings were confirmed and the FDA ordered a stringent black-box warning to appear on the labels of anti-depressants.

The relationship between the FDA and the drug companies has triggered congressional investigations in the United States. But when it comes to revealing data and FDA analyses, Dr Temple said that non-approved data - as well as some safety and efficacy data regarding drugs currently on the market - is "proprietary information" and that it would be a "criminal offence" to reveal it. "That is something only Congress can change," he said.

UNDER SUSPICION

Viagra

US officials are investigating reports of blindness linked to the anti-impotence drug. Its makers, Pfizer, said the cases were "rare" and none was reported among the 13,000 people in its clinical trials.

Hormone replacement therapy (HRT)

A review of clinical trials showed HRT increased risk of stroke by 29 per cent. Royal College of Obstetricians and Gynaecologists said it should only be used in the short term.

Vioxx

The arthritis painkiller used by 80 million patients was withdrawn by its makers, Merck, last September. It could have caused 140,000 heart attacks, almost half of which were fatal.

Seroxat

Fears that the drug could cause an increased risk of suicide if prescribed to depressed teenagers led to a ban for under-18s. Side effects include addiction.

Steve Bloomfield