Provided is a novel neurodietary supplement essentially consisting of the amino acids phenylalanine (Phe) and leucine (Leu), which is useful in the diagnosis and treatment of neurological, neuropsychiatric, or sleep disorders. Furthermore, a method of predicting the clinical response of a subject suffering from or being at risk to develop a neurological, neuropsychiatric, or sleep disorder to selective serotonin reuptake inhibitors (SSRI) and possibly other pharmacological agents using the novel neurodietary supplement is described.
