L-tyrosine

Story

Connected to · 2

synergy · 1

Nervous
Tyrosine competes with the branched-chain amino acids and tryptophan for the same transporter (LAT1) into the brain; the enzyme that makes dopamine and norepinephrine is normally close to saturated, so extra tyrosine only helps refill them when these neurotransmitters are being used up heavily, as during short bursts of intense stress.

contrast · 1

L-Theanine
Theanine also enters the brain through the LAT1 transporter, but it acts on excitatory signals such as glutamate, not on the stores of dopamine and norepinephrine. Same entrance, different targets once inside.

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It competes to enter the brain

EVIDENCEREVIEW 1

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To get into the brain, tyrosine has to compete with several other amino acids for the same door. That door is LAT1, the large neutral amino acid transporter of the blood-brain barrier: a carrier protein set into the lining of the brain's blood vessels that moves tyrosine, tryptophan and phenylalanine, and also the three branched-chain amino acids () — leucine, isoleucine and valine. They are competing for the same seats, not walking through separate lanes.

A 2013 review by Fernstrom sets out the direction of this competition clearly: when blood tyrosine rises, more tyrosine enters the brain; when blood BCAA rise, less tyrosine and less tryptophan get in. The brain uses tyrosine to make catecholamines (the dopamine and norepinephrine family) and tryptophan to make serotonin (5-hydroxytryptamine), and the output of both production lines follows how much comes through the door.

So the useful question about a tyrosine supplement is not how powerful one capsule is, but which amino acids are holding the door in your blood right now. The Nervous System story uses BCAA crowding out tryptophan to explain the same door; this one fills in tyrosine's side.

Educational content, not medical advice — consult a clinician.

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