London, April 22 (IANS): The widely held belief that depression is due to low levels of the chemical serotonin in the brain -- and that effective treatment raises these levels - is a myth, says a leading British psychiatrist.

Professor David Healy from Hergest psychiatric unit in North Wales, points to a misconception that lowered serotonin levels in depression are an established fact, which he describes as "the marketing of a myth".

The serotonin reuptake inhibiting (SSRI) group of drugs came on stream in the late 1980s, nearly two decades after first being mooted, Healy pointed out.

Drug companies marketed SSRIs for depression, "even though they were weaker than older tricyclic anti-depressants, and sold the idea that depression was the deeper illness behind the superficial manifestations of anxiety," he explained.

The approach was an astonishing success, "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."

In the 1990s, no one knew if SSRIs raised or lowered serotonin levels, he writes; they still do not know. There was no evidence that treatment corrected anything, he argued.

He suggests that the myth "co-opted" many, including the complementary health market, psychologists, and journals.

But above all the myth co-opted doctors and patients, he said. "For doctors it provided an easy short hand for communication with patients. For patients, the idea of correcting an abnormality has a moral force that can be expected to overcome the scruples some might have had about taking a tranquilliser, especially when packaged in the appealing form that distress is not a weakness."

Meanwhile more effective and less costly treatments were marginalised, he noted.

The article appeared in the journal The BMJ.