D: Tyrosin ist die Vorstufe einiger Hormone (zum Beispiel der Schilddrüsenhormone Thyroxin-T4 und Triiodthyronin-T3) und verschiedener Neurotransmitter (Katecholamine), wie zum Beispiel Adrenalin, Noradrenalin und Dopamin. Daneben ist Tyrosin auch Vorläufer für die Synthese des Pigments Melanin und des Coenzyms-Q10. Tyrosin verhindert Schläfrigkeit am Tag, Einschlafen bei Nacht, kann die Müdigkeit nach dem Essen verhindern, wirkt antidepressiv.

E: L-Tyrosine is considered a "conditionally essential" amino acid, due to the fact that there are circumstances where the body cannot produce enough to meet physiological needs. Tyrosine is important for the production of the catecholamines, including epinephrine, norepinephrine, and dopamine. Because Tyrosine is involved in the production of the stress hormones epinephrine and norepinephrine, in times of stress the body may not be able to make enough tyrosine from phenylalanine to meet dietary needs. It is also a participant in the function of organs responsible for making and regulating hormones, including the adrenal, thyroid, and pituitary glands. Additionally, it is involved in the structure of almost every protein in the body.