A recent paper showing that drug trials do not support the effectiveness of antidepressants in all but the most severe cases of depression has surprised many psychiatrists.

It ought not to have, similar research having been published at least six-years-ago, but the atmosphere has changed because other concerns about antidepressants have emerged in the meantime. A common response has been to question the adequacy of the trials used to evaluate antidepressants.

There is no doubt that these trials are too brief, that patients are not representative of those seen in clinical practice, and most importantly that the wrong outcomes are measured — scores on depression scales rather than mortality, hospitalisation and productivity. Some psychiatrists, like Gordon Parker from University of New South Wales, have expressed reservations about trials in antidepressant research for some time.

But most antidepressant supporters were silent on the shortcomings of these trials for as long as publication bias and selective reporting had allowed a positive impression of their outcomes. Now that research evidence no longer suits their argument, advocates seek other sources of information to confirm their wishful thinking about antidepressant effectiveness.

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Most favoured are studies that suggest a relationship between increased antidepressant prescribing and decreases in suicide. For example, Ian Hickie, a prominent advocate for increased diagnosis and treatment of depression, recently told Channel Nine’s Sunday that there is “clear cut evidence that increased treatments for depression in Australia has resulted in decreased suicides in Australia. So, more people treated, medicine, psychological counselling, support – less dead people.”

It is not clear to what evidence Hickie refers. Ecological studies look for an association between measure suicide rates and antidepressant usage at a population level. Cohort studies compare suicide levels in patients with and without various treatments. Ecological and cohort studies can not show cause and effect, and there is no ecological or cohort study suggesting a protective effect for antidepressants that cannot be balanced with a study of similar methodology that shows the opposite. Drug trials may show a significant increase in suicide in adults and unequivocally show an increase in suicidal behaviour (but not completed suicide) in adolescents.

Hickie also reassures us that “from the large evidence base that we have there is not systematic evidence of over-prescribing in Australia.” Maybe things are different in Australia, but a 2005 UK study showed that only 3% of those receiving antidepressants from GPs had severe depression.

Hickie then wrote an opinion piece in The Weekend Australian. He drew on data published in the American Journal of Psychiatry to support the claim that reduction in antidepressant prescribing secondary to increased government warnings was associated with increasing suicide rates. But subsequent correspondence in that journal showed that the claimed association was spurious.

There is no convincing evidence that antidepressants reduce suicide. There is convincing evidence that they increase suicidal behaviour in younger patients. We can not be confident about which patients, if any, should receive antidepressants, but we can be confident that many people who are prescribed antidepressants should not be.