What is serotonin?
Serotonin (5-HT) is a chemical messenger that works both in the brain and in the body. About 90 to 95% of the body's serotonin is made by enterochromaffin cells in the gut lining, where it controls gut movement; much of it is carried in blood platelets. Serotonin cannot cross the blood-brain barrier, so the brain makes its own from the amino acid tryptophan, in neurons of the brainstem raphe nuclei.
What does serotonin do?
- •Mood and emotion — shapes how we process emotional information, anxiety and impulse control
- •Sleep — the raw material for melatonin
- •Appetite and pain — helps regulate both
- •Gut and blood — controls gut movement and helps blood clot
Is low serotonin the cause of depression?
Not in a simple way. A 2022 umbrella review found no consistent evidence that depression is caused by low serotonin, although antidepressants that act on serotonin do work better than placebo on average. Blood and urine serotonin tests mostly reflect the gut and platelets, not the brain.
Read more: What does serotonin actually do?