The idea that depression is caused by low levels of serotonin and that certain antidepressants raise the levels of this neurotransmitter, is a myth, according to a professor of psychiatry writing an editorial article in The BMJ.

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The serotonin story has 'distracted' us from other biological avenues of understanding depression.

Prof. David Healy - author of the 2004 book Let Them Eat Prozac: The Unhealthy Relationship Between the Pharmaceutical Industry and Depression - argues in the journal's latest issue that selective serotonin reuptake inhibitors (SSRIs) have never shown any correlation between a potency of serotonin effect and treatment of depression.

Prof. Healy writes that, in the 1990s: "No one knew if SSRIs raised or lowered serotonin levels; they still don't know. There was no evidence that treatment corrected anything."

SSRIs are a class of several drugs for mood disorder - they include the high-selling examples citalopram (Celexa), fluoxetine (Prozac and other brands) and sertraline (Zoloft).

The idea that low levels of serotonin are responsible for depression has been "the marketing of a myth" started by drug companies after the 1980s, when concerns had been emerging about tranquillizer dependence. This marketing of SSRIs for depression took place "even though they were weaker than older tricyclic antidepressants."

The companies "sold the idea that depression was the deeper illness behind the superficial manifestations of anxiety," Prof. Healy says, describing an "astonishing success" of the approach - "central to which was the notion that SSRIs restored serotonin levels to normal, a notion that later transmuted into the idea that they remedied a chemical imbalance."

Serotonin idea 'mis-sold' but 'not irrelevant'

Prof. Healy is an adviser to the Foundation for Excellence in Mental Health Care, which is a proponent of mental health care and research that is focused on recovery, moving away from pharmaceutical bias.

A psychiatrist and psychopharmacologist, his main areas of research are clinical trials of psychiatric drugs, the history of psychopharmacology, and the impact of both trials and psychotropic drugs on culture, says his online profile.

He stresses in his editorial that serotonin "is not irrelevant" but that the marketing history he describes "raises a question about the weight doctors and others put on biological and epidemiological plausibility."

That sales pitch has included, he writes, the "co-opting" of many groups into the idea, including those in the complementary health market, psychologists and journals. "Above all, the myth co-opted doctors and patients."

Prof. Healy asks whether "a plausible but mythical account of biology and treatment" has allowed "everyone" to put aside clinical trial data that show "no evidence of lives saved or restored function."

Such questions are important, he argues, when we take a consumer attitude to psychopharmacological drugs being "products:"

"In other areas of life the products we use, from computers to microwaves, improve year on year, but this is not the case for medicines, where this year's treatments may achieve blockbuster sales despite being less effective and less safe than yesterday's models."

Serotonin has the chemical name 5-hydroxytryptamine (5-HT). It is found in the central nervous system, where is has a role in neurotransmission - the conduction of electrical messages between nerves. Less well known is that it is abundant in the gastrointestinal tract, where much of its production takes place - and a cell-based study this week suggests that gut microbes are important for serotonin production.