The biology of tryptophan depletion and mood disorders.

The involvement of the serotonergic system in the pathophysiology and treatment of affective disorders has been strongly implicated. The tryptophan depletion paradigm is widely used to study the effect of lowering serotonin levels. However, the effects observed in such studies are inconsistent and sometimes contradictory. The present review summarizes and discusses these discrepancies, emphasizing the importance of methodological details such as acute versus chronic tryptophan depletion, patients diagnosis and disease state: euthymic versus acute phase and previous drug treatment. Acute tryptophan depletion as a predictive test for personalized antidepressant treatment is suggested.