The bottle in your hand holds 500 milligrams and suggests one to three a day.
The trial at the centre of this article used 150 milligrams per kilogram of body weight. For a 70-kilo adult that’s ten and a half grams — twenty-one capsules, in one sitting, an hour before you needed it.
That gap is worth understanding, but it isn’t the most interesting thing here. The most interesting thing is a study that gave people the full dose and then had them do two different tasks.
The trial that ran an easy task next to a hard one
Twenty people — ten men, ten women, active-duty personnel and government civilians in Washington DC — took 150 mg/kg of L-tyrosine or placebo an hour before testing (Thomas, Lockwood, Singh and Deuster, Pharmacology Biochemistry and Behavior 1999;64(3):495–500).
Then they did two batteries. The Multiple Task battery measured working memory, arithmetic, and visual and auditory monitoring — all at once. The Simple Task battery measured working memory and visual monitoring, and nothing else.
Tyrosine significantly enhanced accuracy on the working memory task during the Multiple Task battery, and participants needed to consult the list less often.
Then the nulls, which are the actual finding. No significant change on the arithmetic, visual or auditory tasks even within the multitasking battery. And no modification of any performance measure during the Simple Task battery at all.
Same people. Same dose. Same hour. It worked on the hard battery and did nothing on the easy one.
One detail from that trial is worth pulling out, because it’s the closest thing here to your own conditions. ACTH and cortisol did not rise during the testing — but heart rate and blood pressure did. The load was demanding without producing a classical stress response. That is a working afternoon, not an emergency.
That’s the entire product, demonstrated inside a single study. Tyrosine isn’t an enhancer. It’s a substrate top-up for a system being drained faster than it refills — and when nothing is draining it, there’s nothing to top up.
The mechanism agrees. Tyrosine is the precursor the body converts into dopamine and noradrenaline. Under load those get consumed faster than they’re made, and extra raw material helps. In a rested person, tyrosine supply isn’t what limits the reaction, so adding more does very little.
A second demonstration comes from a different direction. In a 1994 trial, 150 mg/kg in eight healthy men reversed a cold-induced working memory deficit at 4°C — a result described in the Dutch cadet study’s own introduction as preventing the impairment observed in the placebo group. When the same test was repeated at a comfortable 22°C, the supplement had no additional effect.
Two things about that. Eight people is a very small trial, and I’m giving you its number because the article’s argument leans on it. And the 22°C null reaches me through two secondary sources rather than the paper itself, so treat it accordingly — though it points the same way as Thomas, and Thomas I have from the primary.
The researchers had run the same experiment in rats a year earlier, at 2°C against 22°C, with the same result. The human study was a translation of an animal finding, which is the direction this evidence travelled.
Where this compound was studied
Four degrees Celsius. Altitude with hypoxia. A night without sleep. One week into a combat training course. And two mock interrogations during several days of simulated captivity at survival school.
Three of the human trials come from defence research institutions: the Royal Netherlands Army, which commissioned the cadet study; the Uniformed Services University of the Health Sciences, which ran the multitasking trial; and the US Army Research Institute of Environmental Medicine. A 1992 paper states the framing in its title — tyrosine as a countermeasure to performance decrement in military sustained operations.
This compound was studied to keep soldiers functional in extremity. It’s sold to people having a demanding Tuesday. The multitasking trial is the closest anyone has come to testing the Tuesday, and even there the load was four simultaneous tasks under continuous measurement.
Now the dose, properly
The two trials at the centre of this piece used 150 mg/kg. Across the wider literature, single doses run 100 to 300 mg/kg — and the cadet study used a flat 10 grams a day rather than dosing by weight.
Manufacturers commonly recommend 500 to 1,500 mg per day, with a note that more than 12 grams daily isn’t advised.
A 500 mg capsule is under 5% of the dose in the trial that found the multitasking benefit — a twenty-first of it. At the top of the retail range, 1,500 mg is about a seventh.
And if you bought the acetylated version, there’s a second multiplication. N-acetyl-L-tyrosine is sold as better absorbed on the strength of being far more water-soluble. It is more soluble — that’s why it exists, for intravenous nutrition, where solubility is the actual constraint. In the one human study I could find, eleven volunteers received 5 g of it as a four-hour intravenous infusion: plasma tyrosine rose 25%, and 56% of the infused amount came out in the urine within four hours. Humans deacetylate it slowly and the kidneys reabsorb it less efficiently than plain tyrosine.
That was an infusion, not a capsule, and nobody has published the oral comparison I’d want. So I can’t tell you the oral figure. What I can tell you is that the acetylated form’s advantage is solubility, and solubility is not your problem.
For timing, if you’re doing this anyway: plasma tyrosine peaks one to two hours after ingestion and can stay elevated up to eight. The trials dosed 60 to 90 minutes ahead. In one sleep-deprivation study, 150 mg/kg split into two doses significantly reduced performance decline on a psychomotor task and lapse probability on a vigilance task, and the improvements lasted about three hours.
What the reviews say — including about themselves
A military review assessed 10 randomised controlled trials and 4 controlled clinical trials against SIGN 50 and GRADE. No recommendation for physical performance under stress. A weak recommendation in favour for cognitive stress, on the grounds that all the studies showed a positive effect.
And then, in its own words: “the available evidence is insufficient to make confident recommendations.”
Every study positive, and still insufficient. A later paper explained the gap — the favourable articles “possessed several methodological limitations,” including lack of randomisation and allocation concealment.
A 2020 systematic review screened 394 studies of supplements and cognition in healthy young adults and military personnel, and included 37. Its verdict on the field: 72.97% of the research was “deemed low quality.” Its recommendation, in the same paper: tyrosine or caffeine could be used in healthy young adults in a military context to enhance cognitive performance when sleep-deprived.
Two supplements out of everything that review covered got a suggestion. Tyrosine was one — attached to “73% low quality.” Both halves are the finding.
Examine’s summary is the best-hedged version I found: no evidence that supplementation improves memory function from baseline, but it may attenuate a decrease in memory formation associated with acute stressors.
The safety section isn’t a formality here
Most supplements covered on this site have nothing worth writing here. This one does — in both directions.
Start with the reassuring part. The sleep-deprivation trial’s authors described 150 mg/kg as “a relatively benign treatment at this dose.” That is the closest thing to a safety statement anyone in this literature offers, and it comes from a primary paper. What I could not retrieve, in any trial, is adverse event rates against placebo. That absence is a gap in my reporting, not evidence of safety.
In older adults, more made it worse. A double-blind randomised crossover gave seventeen adults aged 60–75 single doses of 100, 150 and 200 mg/kg — the same people receiving each dose — with seventeen young adults at 150 mg/kg for comparison. Plasma tyrosine rose dose-dependently in the older group (p < 0.001), and higher than in young adults at the same dose (p < 0.001). Load-dependent working memory performance decreased with higher doses (p = 0.048), especially in those with the greater plasma responses (p = 0.035).
You’re probably not 60–75. But this is the only dose-response trial in the topic, and it kills any “if a little helps, more helps” reasoning.
At double the standard dose, under extreme stress, it increased anger. Military personnel were randomised, double-blind, during survival school — the paper reports 78 participating, with 36 in each arm. The dose was 300 mg/kg total, given as two doses of 150 mg/kg in food bars, an hour before each of two mock interrogations conducted across several days of simulated captivity.
The stress itself did what severe stress does: raised tension, depression, anger, fatigue, vigour and confusion, plus cortisol and heart rate, all p < .001. Against that background, tyrosine increased anger (p = .002) and had no other effects — at the third and fourth test sessions, during the captivity phase.
Three things belong with that number. The dose was double every other trial here — 21 grams for a 70-kilo adult. The stressor was mock captivity. And the authors’ own reading is that the modest increase in anger “may be an adaptive emotional response in stressful environments.” That’s their interpretation and I’m reporting rather than adopting it: “possibly adaptive under interrogation” isn’t obviously reassuring to someone eyeing a capsule before a difficult meeting.
Note also what didn’t move: tension, depression, fatigue, vigour, confusion, cortisol, heart rate. One subscale changed. That makes it narrower and more believable.
The mood results don’t agree with each other. A 1989 trial at 100 mg/kg under cold plus hypoxia reported fewer stress symptoms — headache, tension, fatigue. The Dutch cadet trial at 10 g/day reported improved memory and tracking and lower blood pressure, with no mood effect at all. The survival-school trial at 300 mg/kg reported increased anger and nothing else. Three doses, three stressors, three different answers about how it makes you feel.
The response depends on who you are. One randomised trial’s title states that effects on working memory and inhibitory control are determined by DRD2 genotype. Another reports a baseline-dependent effect on working memory gating but not updating. And the review literature notes that stress-induced impairments were reduced more in individuals particularly sensitive to the stressors to begin with.
And there are real contraindications — not universal, but not theoretical either: MAOIs, hyperthyroidism or Graves disease, levothyroxine, and levodopa, the last through transporter competition, with advice to separate by at least two hours. To be exact about the tier: these come from drug-interaction references rather than from tyrosine trials. They’re mechanism-based precautions, not documented events. If any applies to you, that’s a conversation with whoever writes your prescriptions.
Finally, and this is the largest gap of all: there is no chronic-use data. Every trial retrieved here is acute — a single dose, or a course lasting a week. Nobody has published what happens to someone taking this daily for months, which is precisely how the product is packaged and sold.
What I’d do with this
Rested, ordinary day: nothing. No evidence of improvement from baseline, the mechanism argues against it, and the simple-task battery found nothing.
Before something genuinely demanding, if you want to try it: do the arithmetic first. Work out 150 mg/kg for your weight and compare it with the bottle. If the answer is “my capsule is a twentieth of the trial dose,” you now know what you own. Taking twenty capsules is not the conclusion — the only dose-response trial found performance declining as dose rose.
Buy the plain form, not the acetylated one. The solubility advantage solves a problem intravenous nutrition has and you don’t.
Take it 60 to 90 minutes before, and not daily. That’s how every trial dosed it — and there is no data at all on daily use over months.
Don’t expect a mood change, and don’t be surprised by one. Three trials, three answers.
Read the interaction list before the marketing. This is one of the few compounds here where the contraindications are specific enough to matter.
Here’s the prediction I’d make. If someone runs a proper trial of tyrosine at 500 to 1,500 milligrams — the amount actually sold — against a realistic working day in normally-rested adults, it will find nothing. Not because the compound doesn’t work, but because that trial asks somewhere between a twentieth and a seventh of a dose to show up in the one condition where the full dose already does nothing.
Until then, what’s established is narrow and worth having: at 150 mg per kilogram, under enough load to degrade performance, tyrosine sustains working memory and nothing else. Everything past that is inference from soldiers at four degrees.
About this article
Written by Drew Anton. Drew covers behaviour, sleep, and the compounds people take for both — doses, timing, and what the label does and does not tell you. Not a physician or research scientist — reads the primary literature closely and refuses to round up.
Medical review: None. NeuriFuel does not currently have a licensed clinician on the editorial team, and this article has not been medically reviewed. We state this rather than implying an authority we do not have. See our About page for our full methodology.
Sources: Fifteen, comprising seven randomised or controlled human trials, one human intravenous infusion study, one animal study, two systematic reviews with formal quality assessment, one review of the depletion-dependence hypothesis, one paper cited for its framing of the research question, and two tertiary references used for the retail dosing comparison and the interaction list. Funding or institutional provenance was retrievable for three studies and is stated inline: one commissioned by the Royal Netherlands Army, one from the US Army Research Institute of Environmental Medicine, one from the Uniformed Services University of the Health Sciences. For the remainder it was not available in the sources I could reach, and that absence is marked rather than assumed clean. Adverse event rates against placebo could not be retrieved for any trial and that gap is stated in the text. Four cited studies are known to me by title, abstract or description in other papers rather than read in full; where a figure from one of them appears here, it is because a source I did read also attests it, and the tier is flagged at that point. The cold-exposure trial’s 22°C null and the cadet trial’s results both reach me through secondary description and are marked where used. The acetylated-form data is intravenous rather than oral and is labelled as such; no oral comparison was located.
Corrections: Found an error? Write to hello@neurifuel.com with a source and we will fix it and log the correction.
Last updated: 8 August 2026
References
- Thomas JR, Lockwood PA, Singh A, Deuster PA (1999). Tyrosine improves working memory in a multitasking environment. Pharmacology Biochemistry and Behavior 64(3):495–500. DOI: 10.1016/s0091-3057(99)00094-5. PMID: 10548261. Department of Military and Emergency Medicine, Uniformed Services University of the Health Sciences.
- Shurtleff D, Thomas JR, Schrot J, Kowalski K, Harford R (1994). Tyrosine reverses a cold-induced working memory deficit in humans. Pharmacology Biochemistry and Behavior 47(4):935–941. DOI: 10.1016/0091-3057(94)90299-2. PMID: 8029265. Cold-condition result described in reference 4; 22°C null attested by secondary sources only.
- Shurtleff D, Thomas JR, Ahlers ST, Schrot J (1993). Tyrosine ameliorates a cold-induced delayed matching-to-sample performance decrement in rats. Psychopharmacology 112:228–232. PMID: 7871024. Animal study.
- Deijen JB, Wientjes CJ, Vullinghs HF, Cloin PA, Langefeld JJ (1999). Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course. Brain Research Bulletin 48(2):203–209. Performed by order of the Department of Behavioral Sciences of the Royal Netherlands Army. Results reported here via secondary summary.
- Lieberman HR, Thompson LA, Caruso CM, Niro PJ, Mahoney CR, McClung JP, Caron GR (2015). The catecholamine neurotransmitter precursor tyrosine increases anger during exposure to severe psychological stress. Psychopharmacology (Berl) 232(5):943–951. DOI: 10.1007/s00213-014-3727-7. PMID: 25220844. Military Nutrition Division, US Army Research Institute of Environmental Medicine.
- Dose-dependent effects of oral tyrosine administration on plasma tyrosine levels and cognition in aging. PMC5748730.
- Neri DF et al. (1995). Tyrosine and extended wakefulness. Aviation, Space, and Environmental Medicine 66(4):313–319.
- Banderet LE, Lieberman HR (1989). Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans. Brain Research Bulletin 22:759–762. Known by description in reference 4; not read in full.
- Owasoyo JO, Neri DF, Lamberth JG (1992). Tyrosine and its potential use as a countermeasure to performance decrement in military sustained operations. Aviation, Space, and Environmental Medicine 63:364–369. Cited for its framing of the research question.
- Effects of L-tyrosine on working memory and inhibitory control are determined by DRD2 genotypes: a randomized controlled trial. ScienceDirect S0010945216301642. Known by title and abstract framing; results not read.
- Baseline-dependent effect of dopamine’s precursor L-tyrosine on working memory gating but not updating (2020). Cognitive, Affective, & Behavioral Neuroscience. DOI: 10.3758/s13415-020-00783-8. Known by title; results not read.
- Attipoe S, Zeno SA, Lee C, Crawford C, Khorsan R, Walter AR, Deuster PA (2015). Tyrosine for mitigating stress and enhancing performance in healthy adult humans: a rapid evidence assessment of the literature. Military Medicine 180(7):754–765. DOI: 10.7205/MILMED-D-14-00594.
- A systematic review of the effect of dietary supplements on cognitive performance in healthy young adults and military personnel (2020). PMID: 32093203. PMC7071459.
- Jongkees BJ, Hommel B, Kühn S, Colzato LS (2015). Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands: a review. Journal of Psychiatric Research. PMID: 26424423. Known by abstract and by description in later papers; not read in full.
- N-acetyl-L-tyrosine and N-acetyl-L-cysteine as tyrosine and cysteine precursors during intravenous infusion in humans. ScienceDirect 002604958990005X. Intravenous, not oral. Plus: Examine.com research summary on L-tyrosine and Drugs.com natural products monograph on tyrosine, both tertiary and flagged in the text.