The government is to strengthen the law on disclosing drug trial results following a four-year inquiry into GlaxoSmithKline's delay in reporting data linking its antidepressant Seroxat to suicide risk in teenagers.

"We will take immediate steps to ensure the law is strengthened, so that there can be no doubt as to companies' obligations to report safety issues," Kent Woods, Chief Executive of the Medicines and Healthcare products Regulatory Agency (MHRA), said in a statement on Thursday.

The watchdog criticised Europe's biggest drugmaker for not handing over clinical data earlier but said criminal charges would not be brought because legislation in place at the time was not sufficiently strong.

"I remain concerned that GSK could and should have reported this information earlier than they did. All companies have a responsibility to patients and should report any adverse data signals to us as soon as they discover them," Woods said.

"This investigation has revealed important weaknesses in the drug safety legislation in force at the time."

The agency advised doctors in 2003 not to give Seroxat to patients under the age of 18, after Glaxo handed over data showing it could increase their risk of suicidal behaviour.

An investigation with a view to criminal prosecution was launched due to concerns that Europe's biggest drugmaker had held the information for some time before this.

In the event, government prosecutors concluded there was no realistic prospect of a conviction and that the case should not proceed to criminal prosecution.

GLAXO'S DEFENCE

Glaxo said it believed it acted properly and that it would work with regulatory authorities and other companies on any action needed to improve legislation.

None of the nine paediatric trials of Seroxat individually showed a clinically meaningful increase in suicidal thinking. It was only when they were analysed together that the trend became clear, the company added.

Seroxat, which belongs to a class of antidepressants known as selective serotonin reuptake inhibitors (SSRIs) that includes Eli Lilly and Co's Prozac, is sold as Paxil in the U.S.

It was never licensed for use by teenagers in Britain, clouding Glaxo's disclosure obligations. There has historically been no requirement for firms to publish clinical trial information for drugs in indications where they are not licensed or marketed.

Since Glaxo did the trials, laws have been amended and require firms to report adverse reactions in any study conducted in Europe.

Most of the Seroxat studies, however, were conducted in the U.S. and the MHRA wants a further law change to require the reporting of adverse reactions wherever research takes place.

The move to tighten rules on disclosure adds to controversy over antidepressants, following publication of research last week suggesting SSRIs help only severely depressed people and work no better than placebos in other patients.

Seroxat/Paxil and Prozac are no longer protected by patents, making them of limited commercial importance to Glaxo and Eli Lilly.

Shares in Glaxo were 1.2 percent lower at 10.52 pounds by 12:30 p.m. Analysts said stock weakness mainly reflected concerns about prospects for asthma drug Advair, after U.S. regulators requested more safety data on it and similar products.