The government yesterday released details of its £170m plan to train 3,600 more psychological therapists in the wake of a study showing that antidepressant drugs such as Prozac are no more effective than a placebo.

About 900,000 more people will be treated for depression and anxiety under the plan, according to the Department of Health, which predicts that 450,000 of them will be completely cured. The department also believes that 25,000 fewer people will claim sick pay and benefits because of mental health problems.

"The Improving Access to Psychological Therapies programme has already captured the imagination of primary care trusts up and down the country and is transforming the lives of thousands of people with depression and anxiety disorders in the areas that have been involved so far," said Alan Johnson, the health secretary.

A study published in the open access journal PLoS (Public Library of Science) Medicine on Tuesday revealed that Prozac, Seroxat and other antidepressants of the same class had performed no better than dummy pills in the earliest trials in the 1980s. No such analysis has been done before because of the reluctance of the pharmaceutical companies to hand over the full trial results.

Professor Irving Kirsch from the department of psychology at Hull University and colleagues in the US and Canada obtained complete data for all the trials submitted to the licensing authority in the United States under freedom of information rules. When all the data was amalgamated - some of it is unpublished - it became clear that most of the effect of the drugs was a placebo effect.

Mental health groups say doctors have had no choice but to prescribe drugs because of the shortage of therapists, even though the National Institute for Health and Clinical Excellence (Nice) recommends that talking therapies should be tried before drugs are prescribed. "Nine out of 10 GPs say they've been forced to dish out drugs because they don't have proper access to 'talking treatments' such as cognitive behavioural therapy," said Alison Cobb, policy officer at Mind.

In 2006, more than 31m prescriptions for antidepressants were written in the UK, the charity says, of which 16.2m were for SSRIs (selective serotonin reuptake inhibitors), which include Prozac and Seroxat. "The doctors, the patients and campaigners like us have been telling government for years: spend NHS money on talking therapies and don't just pour it into drugs. Some people do benefit from anti-depressants, but they want talking therapies too," said Paul Corry, of Rethink.

Phillip Hodson, a fellow of the British Association for Counselling and Psychotherapy, said 60% of GP practices had offered some sort of counselling for several years, but there were time limits and restrictions.

Patients on antidepressants were urged yesterday not to stop taking them without seeing a doctor. Sheila Hollins, president of the Royal College of Psychiatrists, said: "We must stress that anyone currently taking antidepressants should first contact their own doctor before considering stopping their medication, as is the case with any form of prescribed medication."

Tim Kendall, joint director of the National Collaborating Centre for Mental Health, which put together the guidelines for Nice, said that if they had been asked to approve Prozac, Seroxat and other antidepressants of that class at the time of licensing, on the basis of the information gathered from the Kirsch study, they would have turned them down because of their ineffectiveness. Nice is currently reviewing its advice on the drugs.

The patient

'These drugs worked for me'

Lisa Tanner is a mother of four from Worcestershire

Shortly after my second daughter was born in 2003, I developed severe postnatal depression. I began to worry about the baby dying, started seeing ghosts and developed severe anxiety about leaving the house. I was really very unwell.

When I saw my GP at six weeks he prescribed a drug, Amytryptaline, that made my symptoms much worse, so shortly afterwards I was given Prozac. Within four to six weeks everything felt brighter. I felt like me again. When I discovered I was pregnant less than a year later I was taken off the drug very abruptly, and I plummeted - the hallucinations started again and I had suicidal tendencies. I was very, very scared.

After the birth I saw another GP who prescribed Sertraline, another SSRI that is safe to use while breast-feeding. I felt better within two weeks. I continued to take it very happily all the way through my fourth pregnancy.

I think there is probably always a placebo effect, but I don't accept that these drugs don't work. Not everyone who has suffered depression is the same, but for me SSRIs have definitely helped.

The GP

'The SSRIs definitely help'

Rob Barnett is a GP from Liverpool

I see a handful of people every week who are either feeling down, or have long-standing anxiety, or have symptoms suggestive of depression.

It is true that there are some patients for whom, if I was able to get them some cognitive behaviour therapy or counselling, that is all that would be needed. But I have others who I have no doubt require medication, and for whom the SSRIs have definitely been helpful. I genuinely do not think that the placebo effect can account for everything.

The truth is that counselling is exceptionally difficult to come by on the NHS. We are still talking of waiting lists that can be up to a year, and it is completely impractical to expect most patients to wait that long. You learn that banging your head against a brick wall just causes you a headache.

I am very careful to assess my patients with a standardised questionnaire and I would like to think my first port of call isn't always the prescription pad. It might just mean seeing the patient fairly regularly - that in itself can be therapeutic.

Interviewed by Esther Addley