L-Tryptophan is one of the essential amino acids for the human metabolism and must be part of its diet.
In humans it is the converted into Serotonin or catabolized to kynurenine through the enzyme IDO (indoleamine-2 ,3-dioxygenase). Increased IDO activity is an expression of neuro-endocrine-immunological dysregulation, which is often associated with depressive symptoms such as bipolar disorder (manic depression).