A major inquiry is to be launched into the safety of widely prescribed antidepressant drugs, including Seroxat and Prozac, following a spate of suicides and reports of severe withdrawal reactions.

The Government's medical advisers have caved in to pressure to hold a fully independent assessment of the risks associated with the antidepressants known as SSRIs, or selective serotonin re-uptake inhibitors.

Recently, there have been reports of suicides among patients taking the medication, as well as users describing nightmares, tremors and feelings of violence.

An expert group of the Committee on the Safety of Medicines has been set up to look at withdrawal reactions suffered by users, who may spend months trying to come off the drugs. The group will listen to first-hand experiences, and investigate reports of suicidal behaviour.

Seroxat, the most widely prescribed antidepressant, was hailed a wonder drug 10 years ago when it came on the market. Along with Prozac, it was dubbed a 'happy pill', as both relieved crippling states of anxiety or depression.

It is now prescribed to hundreds of thousands of British patients, and is earning its manufacturer, GlaxoSmith-Kline, more than £100 million a year in UK sales alone. The news about the investigation into SSRIs will come as a blow to the pharmaceutical industry, which has marketed the drugs as safe and effective. For GSK, it comes in the wake of the humiliation of its shareholders' rebellion, which defeated an attempt to give its chief executive, Jean-Pierre Garnier, a £15m pay-off were he to lose his job.

Last year, more than 22 million prescriptions for antidepressants were written out for British patients, most of them for SSRIs. These drugs work by allowing the neurotransmitter serotonin to act properly in the brain, controlling mood swings and levels of consciousness.

Although they lift many people out of depression and do not carry the debilitating side-effects of older tranquillisers such as Valium and Ativan, concerns have grown that some are left with a legacy of problems.

A BBC Panorama report last year led to thousands of calls from families worried that their relatives were being harmed. It revealed that there had been 16 cases of suicides that bereaved families said were linked to the drugs, 47 attempted suicides and 92 cases of patients who had thought of harming themselves or others. Seroxat recently topped the list of drugs reported to have produced serious side-effects.

The Medicines and Healthcare Products Regulatory Authority, which oversees drug safety, has been criticised for not holding a proper investigation into SSRIs. An earlier expert group had to be disbanded last year after it emerged that some members were shareholders in the companies involved.

But this weekend, Professor Alasdair Breckenridge, MHRA chair, announced that it was setting up an expert group of the Committee on Safety of Medicines to carry out a fully independent scientific assessment, which would, for the first time, take into account patient reports. The group, chaired by Professor Ian Weller of the Royal Free and University College London Medical School, will include patients and the results will be made public.

Breckenridge said: 'SSRIs have been kept under close review for five to six years. However, we are aware that there is interest among patients about withdrawal reactions, feelings of suicide and whether these are linked to SSRIs. As a result, there will be an in-depth investigation into these areas.'

He added: 'It is important that we listen to the views of patients who have taken these popular antidepressants, so patient reports are going to form an important part in the assessment of the safety of SSRIs.' But the MHRA also made it clear that it is not about to take immediate action to limit the use of the drugs. In a statement, the agency said: 'SSRIs are an important group of medicines, which help patients who suffer from depression, anxiety, panic disorder and obsessive compulsive disorder. The health benefits of SSRIs are still considered to outweigh the risk of adverse drug reactions.'

The news of the inquiry was welcomed by the mental health charity Mind, which has campaigned for eight years for the Government to listen to patients' experiences of the drug. Richard Brook, its chief executive, will be a member of the expert group.

Sue Baker of Mind said: 'This is very good news. It seems they have listened to the arguments that peoples' experience of psychiatric drugs are vital and should be taken into account.'

Seroxat was hailed as a wonder drug when it came on to the market 10 years ago, along with its rival Prozac. Psychiatrists say hundreds of thousands of sufferers have been helped by SSRIs.

But there are worries that people are not being told about possible side-effects. For some users it can be a terrible experience with electric shock sensations, nightmares and suicidal thoughts.

There have been repeated warnings from experts that SSRIs may not be suitable for all patients. Psychiatrist Dr David Healy said: 'If they aren't the right drug for you they can cause a range of problems, they can make you suicidal, they can throw you into a state of mental turmoil and even if they are the right drugs for you, they can leave you hooked.'

Helen Kelsall, who spent four and a half years taking Seroxat, was prescribed the drug as a teenager. She told Panorama that she suffered headaches, muscle pains, sweating and trembling, as well as shocks that threw her off balance. 'If I knew five years ago what I know now about the drug I never would have taken it. I didn't know what it would do to me.'