100–150 mg/kg before demanding cognitive effort.
Crossover trial: giving tyrosine raised its blood levels, but in older adults (60-75 years) the highest doses did NOT improve working memory and even tended to worsen it, the opposite of what happened in young people. More is not better: in older people tyrosine may not help cognition.
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L-tyrosine is a nonessential amino acid (the body can synthesize it from phenylalanine) whose most relevant biological role as a supplement is to be the precursor substrate of the catecholamines (dopamine, norepinephrine, and epinephrine) and of thyroid hormones; under normal baseline conditions, tyrosine availability is not limiting for the endogenous synthesis of these neurotransmitters and hormones, but in situations of intense acute stress, sleep deprivation, extreme cold, exposure to hypoxia (high altitude), or sustained cognitive demand under pressure, the depletion of brain catecholamines can be one of the limiting factors of performance, and tyrosine supplementation can supply the substrate needed to maintain synthesis under stress.
Unlike most amino acids, whose supplemental effects are modest in people with an adequate protein diet, tyrosine has an interesting profile specifically in contexts of acute or sustained stress where demand exceeds endogenous synthesis, a characteristic that has positioned it as a supplement for military use (training programs under extreme conditions, special operations), for cognitive performance under pressure (students during intensive exam periods, professionals under demand), and, modestly, for athletic performance in adverse conditions.
The indication with the strongest clinical support is the preservation of cognitive performance under acute stress: several military and experimental trials have documented that doses of 100-150 mg/kg of tyrosine (typically 7-15 g in an adult) taken before exposure to acute stress (extreme cold, hypoxia, sleep deprivation, sustained cognitive demand) preserve performance on cognitive tasks (working memory, sustained attention, decision-making) better than placebo, an indication with modest but consistent clinical support.
In ADHD and depressive disorders with a profile of dopaminergic hypoactivity, tyrosine has been used as a nutritional complement with heterogeneous clinical data; some small studies have shown modest improvements, but the results are not consistent and the magnitude of the effect is clearly smaller than that of specific drugs (stimulants for ADHD, antidepressants for depression); tyrosine may have a place as a complement or as a first-line option in very mild cases, but it does not replace pharmacological treatments when these are indicated.
In phenylketonuria (a genetic disorder of phenylalanine metabolism), tyrosine becomes an essential amino acid because the endogenous conversion of phenylalanine to tyrosine is blocked; specific tyrosine supplementation is part of the standard dietary treatment in these patients, a specific clinical indication with solid support.
The doses studied for cognitive performance under stress are 100-150 mg/kg (7-15 g in typical adults), taken 30-60 minutes before the anticipated stress, as a single dose divided into several sips to improve tolerance; the powder has a characteristic bitter taste that is difficult to mask; capsules are a more practical alternative for lower doses; the effect in people without significant cognitive stress is modest, and tyrosine is not a "universal nootropic" but a specific intervention for situations of excessive demand.
Generally well tolerated at moderate to high doses for acute use; the adverse effects described are rare and mild (digestive discomfort, headache, occasionally palpitations at very high doses); people with hyperthyroidism or thyrotoxicosis should avoid it because of tyrosine's role as a substrate of thyroid hormones; those who take levothyroxine should separate their doses because tyrosine may interfere with absorption of the drug; people who take MAO inhibitors (extremely rare in modern clinical use) have an absolute contraindication because of the risk of hypertensive crisis; those who take levodopa for Parkinson's disease should use caution because of interference with absorption of the drug; people with melanoma should avoid high doses because of tyrosine's role as a substrate of melanin; in pregnancy and breastfeeding the specific data as a supplement are limited, although habitual dietary intake is safe; the reasonable clinical position is: as a general supplement for people with an adequate protein diet, the benefits of tyrosine are quantitatively modest and often undetectable; in specific situations of acute or sustained stress (sleep deprivation, intense cognitive stress, extreme environmental conditions) it may be a useful intervention with moderate clinical support.
Information, not medical advice. Scientific evidence reflects the quality of the studies.