L-Tyrosine

What it is

Tyrosine is a non-essential amino acid. Your body makes it itself from phenylalanine and takes it in with protein-rich food, especially dairy products, soy products and meat. A Japanese safety study estimates the usual intake of healthy adults at an average of 39.9 mg per kilogram of body weight per day, about 2.79 g at 70 kg.

Besides the messengers, tyrosine is also used to make the skin pigment melanin and the thyroid hormones. As a supplement, the free form L-tyrosine is almost always sold, less often N-acetyl-L-tyrosine.

How it is supposed to work

The idea is simple and well founded in humans. Under severe stress, the brain uses more dopamine and noradrenaline than it can replenish in the short term. Additional tyrosine is meant to secure the supply. That intake actually raises catecholamine metabolism has been shown: in a four-week study, tyrosine increased the excretion of MHPG, a breakdown product of noradrenaline.

The limitation that follows from this is important. Tyrosine refills an empty store; it does not raise a full store any further. One review sums it up like this: tyrosine only helps if neurotransmitter function is intact and dopamine or noradrenaline are temporarily depleted. That is exactly why it works in extreme situations and hardly at a quiet desk.

A finding on the dose-response curve fits this. In working memory, dopamine follows an inverted U-curve: too little and too much both do harm. Anyone already in the optimal range can overshoot the target with additional supply.

What the studies show

Memory in cold water

Nineteen volunteers completed two 90-minute water immersions on each of three days, once at 35 °C and twice at about 10 °C. Before each immersion they received a bar with 150 mg tyrosine per kilogram of body weight or placebo, double-blind. The cold raised cortisol and impaired memory and choice reaction. With tyrosine, the number of correct answers in the memory test rose and the learning time became shorter.

A night without sleep

The participants worked through an entire night and had been awake for more than 24 hours by the end. Halfway through, one group received 150 mg tyrosine per kilogram, the other cornstarch. Tyrosine mitigated the usual drop in performance in a psychomotor task and reduced the number of lapses in vigilance. The effect lasted about 3 hours.

Cadets in combat training

Twenty-one cadets went through a demanding combat training course. Ten drank a protein-rich drink with tyrosine daily, eleven a carbohydrate drink with the same calorie content. On day 6 of the course, the tyrosine group performed better on a memory task and a tracking task, systolic blood pressure was lower, and mood was unchanged.

Endurance sport: no effect

A meta-analysis evaluated 10 interventions from 8 studies. Neither in time to exhaustion nor in time trials did tyrosine differ from placebo; the quality of evidence was rated as moderate. A newer study with 12 cyclists found an advantage only after the participants had been mentally fatigued for 60 minutes; the authors themselves call this preliminary.

Safety over four weeks

Thirty healthy men each took 0, 1, 2, 3 or 4 g tyrosine per day for 4 weeks in a double-blind crossover study. Blood count, blood chemistry and electrolytes showed no dose-dependent abnormalities, and side effects were as frequent as on placebo. The study was funded by the manufacturer Ajinomoto, and two authors are employed there.

Where the data stop

All positive cognition studies are small and acute, mostly with 19 to 45 participants and a single intake. Whether tyrosine does anything in normal working life, under mild stress or over weeks has not been properly tested by anyone. The assessment for the US military therefore arrived at only a weak recommendation despite consistently positive individual studies. The effect also depends strongly on the starting point: in a study with 45 young adults, the group mean did not change; weak baseline performers improved, strong ones got worse. In healthy older adults aged 61 to 72, tyrosine impaired a form of response control increasingly with age.

For mood and depression, proof is lacking. In a randomized study with 65 depressed patients, tyrosine had no antidepressant effect over 4 weeks, although it measurably raised noradrenaline metabolism. For endurance sport the data are clearly negative; a football study in the heat also found no effect. And one point about the sources: a tyrosine paper by the most-cited research group was retracted by the journal in 2022.

Status, approval and legal

Tyrosine is an ordinary dietary amino acid and is sold in Germany as a food supplement. We could not verify an authorized EU health claim for tyrosine, so advertising with promises about focus or stress should be read with caution. According to our research, there is no official maximum amount from EFSA, BfR or NIH. Tyrosine is not on the WADA 2026 Prohibited List. The cognition studies mostly used 150 mg per kilogram of body weight as a single dose, one study 2.0 g. This is information about studies, not an intake recommendation.

Safety

In the short term, tyrosine is well tolerated: up to 4 g per day over 4 weeks showed no laboratory abnormalities in healthy men. Longer-term data as well as data on women, older people and pregnant women are lacking. Anyone taking an MAO inhibitor should leave tyrosine out: the US prescribing information for the MAO inhibitor phenelzine explicitly lists L-tyrosine among the substances to avoid because of the risk of a hypertensive crisis. People with thyroid disease were excluded from the safety study, and thyroid values were not measured. Harm has not been demonstrated, but data are simply lacking too, so intake in hyperthyroidism or with thyroid medication should be discussed with a physician. In healthy older adults there are also indications that tyrosine tends to impair individual control functions.

Sources

• Attipoe et al., Mil Med 2015 – rapid evidence assessment of tyrosine
• Jongkees et al., J Psychiatr Res 2015 – review of tyrosine under stress
• Mahoney et al., Physiol Behav 2007 – tyrosine and working memory in cold
• Neri et al., Aviat Space Environ Med 1995 – tyrosine in sleep deprivation
• Deijen et al., Brain Res Bull 1999 – tyrosine in combat training
• Jongkees, Cogn Affect Behav Neurosci 2020 – baseline-dependent effect
• Solon-Júnior et al., J Sports Sci 2023 – meta-analysis on endurance
• Gelenberg et al., J Affect Disord 1990 – tyrosine in depression
• Matsumoto et al., Nutrients 2026 – safety up to 4 g per day
• FDA prescribing information Nardil (phenelzine) – DailyMed