[W]hen the level of blinding was high and it was difficult for the investigators, their staff and depressed patients to guess treatment assignment, the differences between these treatments, controls and placebo became quite small. [Kahn and Brown]Antidepressants work. But they do so only because they elicit a large placebo effect. As has been shown time and again by randomized clinical trials the placebo control always nearly reaches the therapeutic rate of antidepressants. In other words, antidepressants are largely just expensive placebos.
However, that is not quite on the mark. Antidepressants are not just placebos; they are active placebos. Meaning, they produce a range of side effects. And unfortunately some of these are quite serious such as increased risk of suicide and harm to others (including murder), particularly among children, teens and young adults. Moreover, a number of antidepressants can become addictive in the sense that depression-like symptoms occur if the drug is abruptly stopped after having been taken for months. These are drug withdrawal symptoms not a relapse of depression.
The best advice, particularly for those with mild to moderate depression, is to keep away from antidepressants and go for non-drug therapies instead. Such therapies also trigger the placebo effect but don't have the adverse effects of pharmacological agents.