The use of antidepressants has surged across the rich world over the past decade, according to the Organisation for Economic Co-operation and Development (OECD), raising concerns among doctors that pills are being overprescribed.
Data from the OECD show that in some countries doctors are writing prescriptions for more than one in 10 adults, with Iceland, Australia, Canada and the other European Nordic countries leading the way.
Separate data from the US show that more than 10% of American adults use depression medication.
Numbers are even rising in China, with the antidepressant market growing there by about 20% for each of the past three years, albeit from a lower base.
Global rates of depression have not risen to the same extent, even though more people than ever before are being diagnosed in some countries.
Cause and consumption
The OECD says in its Health at a Glance report, to be released on Thursday, that the use of antidepressants in milder cases could explain rising consumption levels.
It added that the financial crisis may have been a factor in more recent increases in use, noting that in Spain and Portugal, for example, prescriptions have jumped by more than 20% over the past five years.
Most psychiatrists agree that antidepressants work for people with severe illness but are not supposed to be the first resort for those with mild depression.
Counselling and talking therapies, such as cognitive behaviour therapy (CBT), are recognised as being just as effective over the long term.
"We know that antidepressants work for moderate to severe depression," said Dr Mark van Ommeren, of the World Health Organisation's department of mental health and substance abuse.
"The explosion of antidepressants you see in most countries reflects the fact that lots of people with moderate to severe depression are getting treatment – that's a good thing.
"But the negative thing is that a lot of people are getting antidepressants who shouldn't be getting them. Doctors and healthcare providers should be able to recognise depression correctly so that those who need antidepressants get them and those with only mild cases do not get prescribed."
Modern antidepressants known as selective serotonin reuptake inhibitors (SSRIs), such as Prozac, took off in the 1990s and gained almost cult status with the publication of Elizabeth Wurtzel's book Prozac Nation in 1994.
Doctors were happier to prescribe them because they did not have the addictive properties or side-effects of pills such as benzodiazepines.
But the bubble seemed to burst within a few years, with stories of some, particularly younger, people attempting suicide while on the drugs.
Some companies paid large sums to settle court cases in the US and, in the UK, doctors were warned in 2003 not to prescribe them to patients under 18 years of age.
But the issues around the various medications do not seem to have affected the long-term upward trend.
The OECD figures show that Iceland has the highest prescribing rate at 105.8 doses a day for every 1 000 inhabitants in 2011, up from 70.9 in 2000 and 14.9 in 1989, when it first submitted figures.
Three countries had figures in the 80s in 2011 – Australia, up from 45.4 in 2000 to 88.9 in 2011; Canada was up from 75 in 2007, when it first submitted figures, to 85.9; and Denmark, up from 34.8 to 85.2.
The lowest rate in 2011 was in Chile, where 12.8 daily doses were prescribed for every 1 000 inhabitants. In the UK, rates have roughly doubled over the past decade to 70.7 for every 1 000 people.
Most experts say that antidepressants are over-prescribed for some people but under-used in others.
"Antidepressants are widely oversubscribed to get rid of unhappiness," said Professor Tim Cantopher, consultant psychiatrist with the Priory Group in the UK.
"They were not designed for that. Unhappiness is part of the human condition. But real clinical depression does respond to antidepressants. And not to prescribe in these cases is to sentence an individual to a far longer illness than he or she need suffer."
Harvey Whiteford, Kratzmann professor of psychiatry and population health at the University of Queensland, Australia, said depression was common and the second leading cause of health-related disability.
But in most OECD countries, he said, only about 50% to 60% of those suffering from depression got treatment, although the rates were increasing.
But the sort of treatment people need varies according to their illness, he said.
"There is good evidence that only major depression is likely to respond to antidepressants and other forms of depression much less so," he said.
Drugs vs counselling
Primary care physicians tend to prescribe drugs rather than CBT, although some countries such as Australia and the UK have initiatives intended to increase the amount of counselling available.
"My view is that antidepressants are often prescribed for the increasing numbers of people now coming to treatment for depression (including mild to moderate forms of depression) where CBT would be the better treatment.
Thus, the prescribing rates are going up and some of this prescribing would be for types of depression better treated non-pharmacologically," he said.
A Better Access scheme, which subsidised CBT for common mental disorders, increased treatment rates in Australia to 46% in 2009-2010 from 37% in 2006-207, he said.
"To get access to psychologists for CBT under the scheme required referral from a GP, who made the diagnosis and ruled out medical causes for the anxiety and depression. We hoped this would decrease the prescribing rates of medication with referral to a psychologist being substituted as first-line treatment for mild to moderate disorders. However, what seems to have happened is that most GPs prescribed and referred for CBT."
Marketing ploy Professor Tim Kendall, director of the National Collaborating Centre for Mental Health in the UK, said he doubted if the rise in antidepressant prescription was a result of better recognition of depression in so many countries.
"It's much more likely a testament to the effective marketing by the pharmaceutical industry," he said.
"I also wonder if, in better off countries, which OECD countries are, we don't have time to be depressed and seek chemical solutions to 'get rid of it'."
Dr Jordi Alonso, director of the programme of epidemiology and public health at the IMIM-Institut de Recerca hospital del Mar in Barcelona, Spain, said: "In my opinion, one major issue is that GPs have become familiar with the indications and results of antidepressants.