Those of us care about and research such things have long known that American Psychiatric Association (APA) is the Emperor wearing no clothes when it comes to the efficacy of SSRI antidepressants. The basic premise of the drug industry is that depression is caused by low levels of the brain neurotransmitter serotonin. So if you are depressed, you need a drug that makes more serotonin available in your brain, which is what the selective serotonin re-uptake inhibitors (SSRI) tend to do.
The only problem is that it never has been proven that depression is caused by low levels of serotonin (Lacasse & Leo, 2005), and in fact there is not even any proven correlation. Some of the most recent research suggests that
problems in information processing within neural networks, rather than changes in chemical balance, might underlie depression, and that antidepressant drugs induce plastic changes in neuronal connectivity, which gradually lead to improvements in neuronal information processing and recovery of mood. (Castrén, 2005)Over the long term, the long term is considerable evidence that SSRIs cause neurogenesis, which can improve neuronal connectivity and create new network connections (neuroplasticity). In this way, SSRIs may help over a period of years, but not weeks or months.
One other theory on why some people feel better on antidepressants despite no measurable improvement in depression scores is that raised levels of serotonin create abnormal brain states that relieve the symptoms of depression:
[W]e propose in this Essay that an alternative “drug-centred” model can better explain observed drug effects in psychiatric conditions. This drug-centred model suggests that instead of relieving a hypothetical biochemical abnormality, drugs themselves cause abnormal states, which may coincidentally relieve psychiatric symptoms ( Table 1). (Moncrieff & Cohen, 2006)Finally, there has been a huge bias in the published studies. Most of those published have used severely depressed subjects, the only population known to show any improvement on these drugs. More importantly, one study found that of 74 studies registered with the FDA, 94% of those published showed positive outcomes, while only 51% of the total showed positive outcomes (Turner, et al, 2008). This does not even take into account the questionable statistical games drugs companies use to generate outcomes.
With that background, here is the CBS segment from 60 Minutes, along with an additional segment not aired that discusses the placebo effect.
Treating Depression: Is there a placebo effect?
How the powerful placebo effect works
Finally, here is a link to the APA's response posted at their website.