"I don't think there's any convincing body of data that anybody has ever found that depression is associated to a significant extent with a loss of serotonin," he says.
Delgado also makes this argument. In the 1990s he carried out a study that showed that if you take a normal person and deplete them of serotonin, they will not become depressed. He says he feels this demonstrates that low serotonin doesn't cause depression.
I am happy that this is appearing on a national platform like NPR. Certainly, serotonin is important in depression somehow, but the truth is that we do not know what causes depression, and we cannot say that it is an "imbalance of chemicals in the brain." The only evidence that we have for this claim is this: People who are giving medications that increase the amount of available serotonin in the brain recover from depression. But taking that as a premise and then concluding that low serotonin causes depression is exactly like saying that high cholesterol is caused by an deficiency of Lipitor, or that a headache is caused by an imbalance of aspirin.
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