Allergy Research Group.

500 mg L-Tyrosine, an amino acid.

Tyrosine is part of the Thyroid hormones T3 (triiodothyronine) and T4 (thyroxin).
It is part of the catecholamine hormones Epinephrine (adrenalin), Nor-Epinephrine, Dopamine, and Levodopa.
It is a precursor to melanin (skin pigment).