Doctors were yesterday told to stop giving antidepressants to children and people under 18, because of the risks that the pills will make them feel suicidal.

The new NHS guidance marks a watershed in the treatment of children's mental health. It shifts the focus sharply away from the psychiatric drugs that around 40,000 children are thought to be taking for depression, anxiety and other problems. Children with mild depression should be given advice on diet and exercise, the guidance tells GPs. Those with moderate and even severe depression should be offered a three-month course of counselling.

The guidance is likely to cause consternation among GPs who do not have enough counsellors and therapists available to treat all the children who will need help. "The very significant shortage of practitioners able to deliver these therapies is a cause for concern," said Dinah Morley, the deputy director of the charity Young Minds, which applauds the new emphasis on therapy.

The government's National Institute for Clinical Excellence (Nice), which has produced the guidance, says only one drug - Prozac - may help children, and even that carries risks. Only if the "talking therapies" do not work can children be prescribed antidepressants - and even then, only in combination with other forms of counselling and close monitoring for side- effects.

Until recently, most under-18s diagnosed with depression have been treated by their GP and most will have been given a prescription. But in response to growing concern at the potential of the modern antidepressants to make young people feel suicidal - highlighted over several years by the Guardian - Nice has said pills should never again be the treatment of first resort.

In June 2003 the drug licensing body in the UK warned doctors of the risks in prescribing any of the modern antidepressants known as the SSRIs (selective serotonin reuptake inhibitors) for anybody under 18, with the exception of Prozac. All of them had a tendency to increase suicidal thinking, but only Prozac showed any benefit in children to counterbalance the dangerous side-effects.

A study in the Lancet in April last year, which looked not only at trial results the drug companies had published but also those they had not, confirmed the risks to children.

From the mid-90s until two years ago, more and more children who were diagnosed with depression were given tablets by their doctors. The SSRIs were much better tolerated than older antidepressants and were thought very safe for GPs to prescribe. The annual number of prescriptions to those under 18 soared from 13,227 in 1995 up to 27,658 in 2003.

But then the few clinical trials carried out in children had shown that the drugs had serious risks. Some children felt suicidal. That was the case with adults too, but significant numbers of adults appeared to recover from their depression. In children, there was not significant evidence, except for Prozac, that the SSRIs had any benefit to set against the risk. This only came to light because GlaxoSmithKline, British manufacturer of the bestselling SSRI, Seroxat, applied for a licence for the drug to be used in depressed children. It submitted the trial evidence it had to the Medicines and Healthcare Regulatory Authority (MHRA), which regulates drugs.

The data showed that 3.4% of children experienced mood changes, tried to harm themselves or thought of suicide, compared with 1.2% who took a dummy pill in the trials. At the time, there were 8,000 children on Seroxat. In June 2003 the MHRA put out a warning to doctors that they should no longer prescribe it to under-18s. In September they issued a similar warning for a second drug, Efexor. On December 11 the MHRA told doctors all the drugs, except for Prozac, were unsuitable for children, although it left it up to doctors to decide whether or not to continue using them, and many are thought to have done so.

Tim Kendall, joint director of the National Collaborating Centre for Mental Health, who was one of the authors of the Lancet study and also led the formulation of the Nice guidelines, said they were even more clear now about the risks. "No child, however severe the depression, should have their firstline treatment with a drug," he said.

He and his colleagues are concerned about the numbers of children with depression, which is sometimes triggered by a sad event like a death, but is often linked to poverty, deprivation, abuse and family breakups. "Our view is that we should be targeting these children as best we can," he said. "Out of 1,200 kids in a comprehensive, at least 40 would be expected to suffer a diagnosis of depressive illness and only 10 are getting any help."

The new guidance for doctors says GPs should advise children with mild to moderate depression on ways they can help themselves through exercise and diet. "But then if there is any significant risk, we should be offering individual cognitive behaviour therapy or family therapy, depending on their needs," he said. "We're really serious that we don't think these drugs should be used lightly."

Even when a young person is severely depressed, the first step should be psychotherapy for around three months. Only if there has been no improvement after four or five sessions should the doctor - and by this stage it would be a psychiatrist - consider prescribing Prozac.

Andrew Dillon, chief executive of Nice, said the guideline "makes it clear that psychological treatments are the most effective way to treat depression in children and young people." Children taking pills should talk to their GP about phasing them out.

At present, there are not enough counsellors and therapists to help all the children who may need it. Yesterday Louis Appleby, the national director for mental health, said: "We know that not everyone who needs treatment is able to access it easily or quickly and expertise and services are not equally distributed around the country." He added that the government was "considering ways of increasing numbers of staff" trained in cognitive behaviour therapy, which is usually the preferred treatment for depression. More than £300m had gone into child and adolescent mental health services.

Mind, the mental health association, urged the government to give the NHS the support and resources it would need to ensure children have proper access to psychological treatments. Research on antidepressants "has shown many to be totally unsuitable for young people. They must be provided with effective alternatives," said a policy officer, Alison Cobb.

"These guidelines are a welcome step in the right direction: the onus is now on the government to provide the means to make them happen," said Liz Nightingale of the mental health charity Rethink.

Danger signs

In 2003, under-18s in England were given 27, 658 prescriptions for antidepressants

40,000 children and young people are thought to be on psychiatric drugs, including antidepressants

Doctors were warned in 2003 of the risks of using Seroxat, Efexor, Lustral, Cipramil, Cipralex and Faverin in children and young people

A survey of GPs in March 2004 found 80% thought they were prescribing SSRIs to too many adults and children