By Michelle Roberts
BBC News health reporter
Recent concerns over the safety of painkillers used by millions of patients call into question whether regulatory checks on the medicines we take are adequate.
The safety review on COX-2 inhibitors is expected to report soon
One of the US Food and Drug Administration's own scientists, Dr David Graham, has publicly accused the drug regulator of profound failure in its role.
Both the FDA and the European Medicines Agency (EMEA) are reviewing their policies.
COX-2 inhibitors are used mainly for arthritis and are designed to be gentler on the stomach than other non-steroidal painkillers.
The COX-2 story began in September when Merck voluntarily withdrew its blockbuster drug Vioxx (rofecoxib) from the market after data showed users had a 50% higher chance of a heart attack and sudden cardiac death.
Three months later, research showing another COX-2 inhibitor Celebrex (celecoxib), produced by Pfizer, posed a similar threat to users led to fears that it might be an effect common to all drugs in this family.
The safety of other approved drugs also came into question last year.
There was controversy over the possible increased risk of suicide in children taking SSRI antidepressants.
The Lancet accused drug companies of failing to publishing "unfavourable" studies.
Researchers made similar allegations in the Journal of the American Medical Association related to data on a statin drug and some 100 deaths.
The FDA said it evaluated the safety and effectiveness of all drugs independently on a case-by-case basis before they are approved to enter the marketplace.
It also evaluated reported adverse events with all drugs already on the market to assess whether unforeseen safety concerns need to be addressed.
Dr Steven Galson, Acting Director, Center for Drug Evaluation and Research said: "The FDA takes all allegations of safety risks seriously and will continue its longstanding practice of assessing the safety of all drugs using only sound science and peer-reviewed analysis and literature."
In Europe, the European Commission referred the COX-2 issue to the EMEA and its scientific committee, the Committee on Medicinal Products for human use (CHMP) for evaluation.
On 21 December the summary data from two clinical trials on the cardiovascular risk related to celecoxib were provided to the EMEA.
Based on these summary data the EMEA/CHMP decided to accelerate its review of COX-2 inhibitors.
Its verdict will influence how drugs are prescribed in the UK.
A spokesman said: "The drug companies followed all of the licensing and regulatory requirements.
"It is not until drugs go out into the world and they are used in real patients that they hit larger populations.
"Sometimes then you may pick up side effects that we hadn't been able to see during clinical trials.
"We have a system in place to monitor these side effects. Both the companies and doctors report side effects to the regulators.
"This allows us to change the indication if need be or in extreme cases pull the drug off the market."
Jane Tadman of the Arthritis Research Campaign said: "The heart and stroke risks associated with Vioxx were known about for almost five years, and yet none of the drug regulatory bodies did anything about it.
"The regulatory system regarding the licensing and monitoring of drugs urgently needs tightening up to prevent this kind of debacle happening again.
"We'd also like to see pharmaceutical companies acting more responsibly and to be legally required to make public any data that is unfavourable to their product, in the interests of public safety.
"We're glad that the EMEA are speeding up their safety review of all COX-2 inhibitors, and should be announcing its recommendations later this month.
"To be fair to the EMEA, it carried out a similar review a couple of years ago, and as a result the warnings about the drugs and who should be prescribed them were tightened up, so that no-one at risk of heart attack or stroke should be given them."
A spokeswoman from Merck said the drug regulators had been very rigorous in their conduct and that Merck had shared its drug safety information at the soonest opportunity and acted quickly.
Pfizer said: "We have a sophisticated system to ensure that we fully comply with national reporting standards.
"We review all medicines proactively and take appropriate action working with regulators if we discover any signals which may be of concern."
Some say the FDA needs to change the way it monitors drugs and decouple the process from the original licensing procedure.
The FDA says its Center for Drug Evaluation and Research is already an independent office separate from the Office of New Drugs.
In England, drug regulators will be barred from having any links to the pharmaceutical industry in the future.
A new commission will be formed to advise ministers on the safety and effectiveness of medicines combining the responsibilities of the Medicines Commission and the Committee on the Safety of Medicine.
The EMEA said new legislation that will come into effect this November will mean drug companies can be required to provide longer-term data on the safety of their products post-authorisation.
A spokesman said: "That could help. We are also working towards a massive electronic database that companies and all the national authorities can use to input adverse events.
"It will allow us to identify [safety] issues much more easily."