Major new study casts doubt on longstanding 'chemical imbalance' theory of depression

A major new study published this week suggests that a longstanding theory of mental depression has little to no evidence to support it.

The study, conducted by an international team of scientists and published in Molecular Psychiatry, argued that the "serotonin hypothesis of depression" is bolstered by "no consistent evidence" despite its popularity among psychiatrists for decades.

That hypothesis has held that depression is caused by what many psychiatrists have termed a "chemical imbalance" in the brain of those who suffer from it. The researchers said a broad review of multiple studies failed to establish that claim. 

"The general public widely believes that depression has been convincingly demonstrated to be the result of serotonin or other chemical abnormalities," the scientists say in the paper. Yet "the huge research effort based on the serotonin hypothesis has not produced convincing evidence of a biochemical basis to depression," they claim.

"We suggest it is time to acknowledge that the serotonin theory of depression is not empirically substantiated," the researchers state in the paper.