This disparity between simple pharmacological effects and clinical experience might be due to the time it takes for serotonin axons to grow. For the patient, this hypothesis provides more tangible evidence of a real effect in the brain.

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But our findings — that serotonin reuptake modulators increase the density of nerve synapses, especially in the front part of the brain — may offer a better explanation of why antidepressants are effective and why they take time to work.

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