On their introduction, Selective Serotonin Re-Uptake Inhibitors, or SSRIs, were heralded as a so-called 'magic bullet' solution to depression. Prescriptions of SSRIs such as Prozac and Seroxat have increased considerably in the UK since the mid-1990s, to around 18,000 prescriptions last year.

BBC Wales' award-winning current affairs programme Week In Week Out highlights concern that, although these drugs have proved beneficial for many patients, a small sub-group of patients may be susceptible to severe withdrawal symptoms after they stop taking one type of drug, and intense agitation leading to suicidal ideation when taking others.

Pharmaceutical companies strenuously deny the claims and insist that the drugs are a safe, effective treatment.

However Doctor David Healy, of the University of Wales College of Medicine, claims his own clinical research into one of the SSRI group of drugs, Lustral - or Zoloft as it is known in the US - shows that it can cause suicidal thoughts in some patients.

Dr Healy, who is director of the North Wales department of psychological medicine at Bangor, was offered a top research job in the Canadian city of Toronto, which was withdrawn after he delivered a lecture in which he claimed that SSRIs could cause a minority of patients to feel suicidal. After a lengthy dispute, he has now reached an out-of-court settlement with his prospective Canadian employers.

Dr Healy conducted his own clinical research study on Lustral two years ago, using a group of colleagues who were not suffering depression. Two of the volunteers became severely agitated and disturbed, and one even developed suicidal thoughts.

This volunteer, Isobel Logan, tells the programme, "I really thought, 'I just want to hang myself.' I felt so low, so depressed."

Dr Healy, who has given expert testimony in a number of high-profile medical negligence cases associated with SSRIs in the US, says, "The extraordinary finding was that when you give these drugs to people who aren't suited to them, you can make healthy volunteers agitated and suicidal on these drugs, within a week or two of them being on the drug."

However, Dr Healys research has been criticised in some quarters.

Meanwhile, a Cardiff firm of solicitors is considering launching a possible class action against the makers of Seroxat, GlaxoSmithKline. Medical negligence lawyer Mark Harvey, of Hugh James Solicitors, has been contacted by around 150 people from across the UK who claim to have experienced problems with Seroxat, including severe withdrawal symptoms when they tried to stop taking the drug.

Mother-of-two Paula Boddington tells the programme that she suffered electric-shock type sensations in her head and an irrational compulsion to harm herself when she tried to come off the drug.

Mark Harvey tells the programme, "People have often gone into their doctors, either feeling stressed or having mild panic attacks, and the doctor says, this tablet will give you a nice pick-you-up, and they feel good ... then they find that, when they go to come off the drug, the doctor understandably thinks that (the withdrawal symptoms) are the original condition, so they re-prescribe, and then they get into this vicious circle where they are taking the tablets more and more, feeling worse and worse."

But GlaxoSmithKline, manufacturers of Seroxat, deny that the drug is addictive.