L-Tyrosine

L-tyrosine is the precursor to both thyroid hormones (T3 and T4) and catecholamine neurotransmitters (dopamine, norepinephrine, epinephrine). In the thyroid gland, tyrosine is iodinated to form monoiodotyrosine (MIT) and diiodotyrosine (DIT), which combine to form T3 and T4. In the adrenal medulla and brain, tyrosine is converted to dopamine and then to norepinephrine.

Addresses the amino acid substrate requirement for both thyroid hormone synthesis and neurotransmitter production. Under chronic stress, tyrosine is rapidly depleted by the adrenal medulla's increased catecholamine production — leaving insufficient substrate for thyroid hormone synthesis.

Studies confirm L-tyrosine supplementation improves cognitive performance under stress, supports thyroid function, and reduces the cognitive deficits associated with sleep deprivation. A 1994 military study showed significant improvement in cognitive performance in cold-stress conditions.

500–2000mg daily on an empty stomach for cognitive effects. For thyroid support, take with iodine and selenium. Avoid in patients with hyperthyroidism or those taking MAO inhibitors.