Too many people are being diagnosed with depression when all they are is unhappy, a leading psychiatrist says.
Prof Parker said prescribing medication may be not be effective
Professor Gordon Parker claims the threshold for clinical depression is too low and risks treating normal emotional states as illness.
Writing in the British Medical Journal, he calls depression a "catch-all" diagnosis driven by clever marketing.
But another psychiatrist writing in the journal contradicts his views, praising the increased diagnosis of depression.
Professor Ian Hickie writes that an increased diagnosis and treatment of depression has led to a reduction in suicides and removal of the old stigma surrounding mental illness.
Under the current diagnosis guidelines, around one in five adults is thought to suffer depression during their lifetime. This costs the UK economy billions in lost productivity and treatment.
Professor Parker, from the University of New South Wales, in Australia, said the "over-diagnosis" began around 25 years ago.
Study of teachers
The professor, who carried out a 15-year study of 242 teachers, found that more than three-quarters of them met the current criteria for depression.
He writes in the BMJ that almost everyone had symptoms such as "feeling sad, blue or down in the dumps" at some point in their lives - but this was not the same as clinical depression which required treatment.
He said prescribing medication may raise false hopes and might not be effective as there was nothing biologically wrong with the patient.
He said: "Over the last 30 years the formal definitions for defining clinical depression have expanded into the territory of normal depression, and the real risk is that the milder, more common experiences risk being pathologised."
But Professor Hickie said if only the most severe cases were treated, people would die unnecessarily.
Marjorie Wallace, chief executive of the mental health charity Sane, said: "Depression can be a complex and challenging condition ranging from feeling low to being so disabled that the person may be unable to get out of bed in the morning, sustain relationships or work.
"It is not surprising that with such a wide range of symptoms, identification varies from one doctor to another.
"Sane believes that it is better to risk over diagnosis than to leave depression untreated. One in ten people with severe depression may take their own life."
The number of prescriptions for antidepressants in England hit a record high of more than 31 million prescriptions earlier this year - a 6% rise in two years.