Commonly used modern antidepressants can cause adults as well as children to attempt suicide, a new study says.

An 18-month inquiry convened by the Medicines and Healthcare Regulatory Authority (MHRA) in the UK banned the use of the drugs, known as the SSRIs (selective serotonin reuptake inhibitors) in children and adolescents.

Last December it said the drugs were over-prescribed though they could safely be used by adults.

But a study published today in the online journal BMC Medicine casts doubt on the MHRA's findings. One of the manufacturers, the British company GlaxoSmithKline, which makes the bestselling Seroxat, did not submit its original detailed data from clinical trials of the drug to the regulator, said the Norwegian author of the report, Ivar Aursnes.

The absence of a detailed breakdown between suicide attempts and suicidal thinking, Dr Aursnes said, distorted the conclusions on the dangers of the drugs.

Using the information from the original trial Dr Aursnes and colleagues found that in 16 trials there were seven attempted suicides among people taking Seroxat, compared to one among those given a placebo.

The data, they write, when added to the information from trials of the other drugs of the class, "strongly suggests that the use of SSRIs are connected with increasing intensity per year of suicidal attempts". They make "a strong case for a conclusion, at least with a short time perspective, of an increased risk of suicidal attempts in adults taking antidepressants".

Dr Aursnes obtained the original trial results from the Norwegian regulatory authority, he said. When the MHRA asked for data on suicides from GlaxoSmithKline, what they received "was not the original science".

The drugs company, he said, provided a summary which added together suicide attempts and reports of patients feeling suicidal.

"I think the UK investigation could have been even more thoroughly done if they had looked through the primary data," he said.

He had attempted to alert the MHRA to his findings, he said. "I have tried but they have not shown any interest."

Dr Aursnes embarked on further analysis after studies in the British Medical Journal in February appeared to give the drugs a clean bill of health in adults. The authors found there was an increased frequency of suicide attempts by people on the drugs, but that it was not statistically significant. Their data came from the MHRA inquiry and did not include full GlaxoSmithKline figures.

GlaxoSmithKline said all its own extensive research into the safety of Seroxat - known also by the generic name paroxetine - confirmed its safety. "We take the safety of all our medicines extremely seriously and will, of course, review this study carefully when it becomes available," said a spokesman. "We can say these conclusions in no way reflect the picture ... about the benefits and risks of paroxetine in adults through an extensive clinical trials programme involving 24,000 patients or through the use of this medicine."

In 2003, doctors wrote some 19m prescriptions for Seroxat for patients with depression and anxiety in England.