Hundreds of thousands of people will be labelled mentally ill because of behaviour most people would consider normal, if a new edition of what has been termed the psychiatrists' diagnostic bible goes ahead, experts are warning.

Psychiatrists and psychologists in the UK are speaking out against the publishing of DSM-5, an updated version of the Diagnostic and Statistical Manual that categorises every type of mental disorder, including some that the psychologists say should not exist.

A petition condemning the new manual circulated by psychologists in the United States attracted 11,000 signatures. Its predecessor, DSM-4, is used in research worldwide, and has an influence, for example, in naming conditions that pharmaceutical companies devise drugs to treat.

However, the DSM's influence is uniquely strong in the United States, where the private healthcare system requires a diagnosis recognised by the manual for the patient to be considered legitimately ill and be reimbursed by the health insurer for any treatment.

Among the anxieties to be labelled mental disorders if DSM-5 is published in May by the American Psychiatric Association are shyness in children and uncertainty over gender. Loneliness could attract a diagnosis of chronic depressive disorder, and so could unhappiness following bereavement. A serial rapist could be classified as mentally ill, given a diagnosis of paraphilic coercive disorder.

Under the DSM-4, last revised 12 years ago, children who argue and refuse to obey parents can be classified as having oppositional defiant disorder.

Professor Nick Craddock, consultant psychiatrist in Cardiff and director of Wales' National Centre for Mental Health, said: "Somebody who is bereaved might need help and even counselling, but they did not need a label saying they had a mental illness. I believe that a large proportion of psychiatrists in the UK and Europe are sceptical about DSM-5."

Peter Kinderman, professor of clinical psychology and Head of Institute of Psychology at the University of Liverpool, said the revisions "could only make a bad system worse". The diagnostic approach, a tick-box list of symptoms leading to a label, was always "hugely problematic", he said. What is termed "oppositional defiant disorder" is dubious, he said: "Since my children say 'no you are an idiot, dad' repeatedly to me, by definition my children are ill." He also disagreed with the label of paraphilic coercive disorder: "In my view, rape is a crime and should not necessarily be regarded as a disorder. It gives people an excuse for that behaviour," he said."

Til Wykes, professor of clinical psychology at Kings College London, said: "The proposals in DSM-5 are likely to shrink the pool of normality to a puddle with more and more people being given a diagnosis of mental illness."

The American Psychiatric Association strongly defends DSM-5. In response to criticism from the British Psychological Association last year, Darrel Regier, vice-chair of the DSM-5 task force. wrote: "While we agree that human feelings and behaviors exist on a spectrum that contains some overlap of normal reactions to disease states, psychiatry also recognizes that there are real and discrete disorders of the brain that cause mental disorders and that can benefit from treatment."