L-Tyrosine is a conditionally essential amino acid that serves as a precursor for important neurotransmitters including dopamine, norepinephrine, and epinephrine. It plays a crucial role in cognitive function, mood regulation, and stress response. Tyrosine is involved in protein synthesis and is a precursor for thyroid hormones and melanin. It becomes essential when phenylalanine intake is insufficient or when the body is under stress.