Mordax et al

…Kirsch’s study and, now, others conclude that the lion’s share of the drugs’ effect comes from the fact that patients expect to be helped by them, and not from any direct chemical action on the brain, especially for anything short of very severe depression.

…in just over half of the published and unpublished studies, he and colleagues reported in 2002, the drug alleviated depression no better than a placebo. "And the extra benefit of antidepressants was even less than we saw when we analyzed only published studies," Kirsch recalls. About 82 percent of the response to antidepressants—not the 75 percent he had calculated from examining only published studies—had also been achieved by a dummy pill.

The extra effect of real drugs wasn’t much to celebrate, either. It amounted to 1.8 points on the 54-point scale doctors use to gauge the severity of depression, through questions about mood, sleep habits, and the like. Sleeping better counts as six points. Being less fidgety during the assessment is worth two points. In other words, the clinical significance of the 1.8 extra points from real drugs was underwhelming. Now Kirsch was certain. "The belief that antidepressants can cure depression chemically is simply wrong," he told me in January on the eve of the publication of his book The Emperor’s New Drugs: Exploding the Anti-depressant Myth.

…But if experts know that antidepressants are hardly better than placebos, few patients or doctors do. Some doctors have changed their prescribing habits, says Kirsch, but more "reacted with anger and incredulity." Understandably. For one thing, depression is a devastating, underdiagnosed, and undertreated disease. Of course doctors recoiled at the idea that such drugs might be mirages. If that were true, how were physicians supposed to help their patients?

…the question of whether antidepressants—which in 2008 had sales of $9.6 billion in the U.S., reported the consulting firm IMS Health—have any effect other than through patients’ belief in them was too important to scare researchers off. Proponents of the drugs have found themselves making weaker and weaker claims. 

…Right about here, people scowl and ask how anti-depressants—especially those that raise the brain’s levels of serotonin—can possibly have no direct chemical effect on the brain. Surely raising serotonin levels should right the synapses’ "chemical imbalance" and lift depression. Unfortunately, the serotonin-deficit theory of depression is built on a foundation of tissue paper. How that came to be is a story in itself, but the basics are that in the 1950s scientists discovered, serendipitously, that a drug called iproniazid seemed to help some people with depression. Iproniazid increases brain levels of serotonin and norepinephrine. Ergo, low levels of those neurotransmitters must cause depression. More than 50 years on, the presumed effectiveness of antidepressants that act this way remains the chief support for the chemical-imbalance theory of depression. Absent that effectiveness, the theory hasn’t a leg to stand on. Direct evidence doesn’t exist. Lowering people’s serotonin levels does not change their mood. And a new drug, tianeptine, which is sold in France and some other countries (but not the U.S.), turns out to be as effective as Prozac-like antidepressants that keep the synapses well supplied with serotonin. The mechanism of the new drug? It lowers brain levels of serotonin. "If depression can be equally affected by drugs that increase serotonin and by drugs that decrease it," says Kirsch, "it’s hard to imagine how the benefits can be due to their chemical activity."