A conditionally-essential amino acid synthesized from L-phenylalanine. L-tyrosine is a precursor to the catecholamine neurotransmitters, l-dopa, dopamine, norepinephrine, and epinephrine – which are important contributors to mood and cognitive performance. It’s also a precursor to the thyroid hormone thyroxine (also known as T4).
In larger amounts, L-tyrosine has been shown to improve memory, psychomotor skills and cognitive performance under physical stress. L-tyrosine is frequently added to weight loss and pre-workout supplements to enhance alertness and (possibly) metabolism, although it is frequently underdosed.
May also be listed as 4-hydroxyphenylalanine.
For more information, see Paul’s review: “L-Tyrosine: Fat Burner & Anti-Depressant?”