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What Serum Serotonin Level Does Major Depression Start At?

Many people have heard that low serum serotonin (5-hydroxytryptamine, or 5-HT) causes depression. Research suggests a link, but not a causal relationship. Major depression can occur at low, normal or high serum serotonin levels; there is no "magic number" where depression starts.

  1. Description

    • Serotonin is a messenger chemical found throughout the body, including the brain. According to Medline Plus, normal blood (serum) levels of serotonin are 101 to 283 nanograms per milliliter (ng/mL).

    Depression

    • The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, notes that "no laboratory findings diagnostic of a major depressive episode have been identified." However, several neurotransmitters, including serotonin, may play a role.

    Link

    • Antidepressants known as selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine and sertraline, increase serotonin and can be highly effective in treating depression.

    Myth

    • According to a study by Jeffrey Lacasse and Jonathan Leo published in "PLoS Medicine" on Nov. 8, 2005, the success of SSRIs led to advertising implying that low serotonin caused depression. This claim had no basis in scientific research.

    Evidence

    • The antidepressant tianeptine works by lowering serotonin, not raising it. Another drug, reserpine, which lowers serotonin, does not cause depression. Peter Kramer, M.D., writes in "Against Depression" that hypotheses linking serotonin to depression "contained part of the truth, but [have become] ever more problematic."

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