Metabolite results when a drug is metabolized into a modified form which continues to produce effects. A metabolome in a given body fluid is influenced by endogenous factors such as age, sex, body composition and genetics as well as underlying pathologies.The levels of the enormous array of unique small-molecule metabolites are usually kept tightly regulated by the activity of a very large array of enzymes and transporters responsible for the production, transformation, degradation, and compartmentalization of these small molecules.The levels of the endogenous small molecules present in the brain are normally tightly regulated.