L-Tyrosine

Tyrosine supplementation · N-Acetyl-L-Tyrosine

Snapshot

Indications	Contraindications
Cognition under stress¹ Working memory under load¹ Decision-making speed^{2, 3} Pre-workout cognitive scores⁴	MAO inhibitor use⁵ Hyperthyroidism or thyroid disease⁵ Melanoma⁵

L-tyrosine is a dietary amino acid and the precursor to the catecholamine neurotransmitters dopamine and norepinephrine. Supplementation is used to buffer working memory and information processing when demanding conditions such as cognitive load or extreme weather deplete catecholamines. It is also taken for exercise-related readiness, often as N-acetyl-L-tyrosine in pre-workout blends⁴, and as an adjunct in phenylketonuria^{6, 7}.

The evidence is conditional. Acute loading counteracts cognitive decrements under stress¹, but a meta-analysis found no effect on endurance performance⁸. A trial in soccer players exercising in heat also found no benefit³. Cochrane reviews of phenylketonuria concluded that no recommendation on routine use can be made^{6, 9}. In a 2026 randomized crossover trial in healthy adult men, four weeks of supplementation caused no clinically meaningful laboratory abnormalities¹⁰. Products listing L-tyrosine number in the thousands, mostly capsules and powders, as free-form or N-acetyl forms; see Form comparison.

In older adults, a single-dose trial linked higher plasma tyrosine responses to poorer working memory¹¹. US product labels ask people taking monoamine oxidase (MAO) inhibitors, or with thyroid disease, to seek a physician's advice before use⁵.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

63 sources, 46 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources