The Food and Drug Administration (FDA) stopped short of stating that the drugs can cause some people to want to kill themselves, but made it clear it was a possibility. Doctors should be aware that if a patient's depression appeared to get worse, it "could be due to the underlying disease or might be a result of drug therapy", the FDA said.

David Healy, the consultant psychiatrist from north Wales who raised concerns about suicidal thoughts and the SSRI (selective serotonin reuptake inhibitors) class of drugs, said yesterday that the FDA announcement was very close to stating that the drugs caused the problems that have been reported.

"They won't use the 'cause' word all that quickly but they have said this happens during the early days of treatment and it also happens when you change the dose. That is as causal as you can get," he said.

"They are hedging their legal bets. Regulators are at real risk of being brought to the courts by pharmaceutical companies that are unhappy with what they have done."

An expert working group was set up by the UK drug regulator, the Medicines and Healthcare Products Regulatory Agency (MHRA), last year to investigate the allegations not only that the drugs made people suicidal and aggressive, but also that they suffered severe side-effects when they tried to stop taking them.

The group looked first at the clinical trial evidence relating to children and found that there were more suicides in those on SSRIs than on the placebo. As a result, the MHRA banned the use of all the drugs except Prozac by those under 18.

But the working group is still examining the evidence in adults. Richard Brook, chief executive of the mental health charity Mind, resigned last week from the group over the MHRA's reluctance to reveal publicly that Seroxat over the minimum dose of 20mg a day was ineffective and led to more side-effects. He now thinks the MHRA should follow the example of the US.

"In view of this decision by the conservative FDA, I think the MHRA must now immediately issue advice to people in the UK over suicidality in adults," he said.

"I fear they won't, because they have a reluctance to engage proactively with this issue, and also because they are concerned about the European licence." The drugs were licensed for the whole of Europe and it is likely that the MHRA would want to wait for a European consensus.

The FDA says that patients on the drugs must be more closely monitored for suicidal thoughts. Karen Barth Menzies, a lawyer with Baum Hedland in the US, which is pursuing legal claims against the companies, welcomed the FDA statement, but regretted that it had taken a decade of pressure to get the bold-print warnings manufacturers will now have to include on labelling.