Tryptophan is an essential amino acid. It is not produced by the human body so it needs to be obtained through diet. Since tryptophan is a biochemical precursor to neurotransmitters, such as serotonin, maintaining proper levels of tryptophan is crucial to mental health.
5-HTP is an amino acid that facilitates the synthesis of serotonin from the essential amino acid tryptophan. Since the synthesis of serotonin cannot take place without it, 5-HTP is also important for mental health.