Tyrosine is one of those supplements that sounds more exotic than it actually is. It’s simply an amino acid, one of the building blocks your body uses to make proteins and several important chemical messengers in the brain.

You might have heard claims that tyrosine can sharpen your thinking, boost your mood, or help you power through stressful situations. Some of these claims have reasonable evidence behind them. Others don’t. This article looks at what the research actually shows.

What is tyrosine?

Tyrosine is classified as a “non-essential” amino acid, which doesn’t mean your body doesn’t need it. It means your body can manufacture it from another amino acid called phenylalanine, so you don’t absolutely have to get it from food.

The word “tyrosine” comes from the Greek “tyros,” meaning cheese, because it was first isolated from casein (milk protein) back in 1846. Quite the history for a humble amino acid.

Your body uses tyrosine as raw material for several compounds:

Dopamine – involved in motivation, reward, and movement
Noradrenaline (norepinephrine) – affects alertness and the stress response
Adrenaline (epinephrine) – the “fight or flight” hormone
Thyroid hormones – regulate metabolism
Melanin – the pigment in skin and hair

You can find tyrosine in most protein-rich foods: cheese, meat, fish, eggs, nuts, beans, and soy products. A typical Western diet provides somewhere between 2.5 and 5 grams daily [1].

The supplement form is usually sold as L-tyrosine or N-acetyl L-tyrosine (NALT). L-tyrosine is the natural form found in food. NALT is more water-soluble but may be less effective because your body converts less of it into usable tyrosine [2].

What are the potential benefits of tyrosine?

1. Tyrosine may help cognitive function under stress

This is where tyrosine has the most interesting research behind it. The theory goes like this: when you’re under stress (cold, sleep deprivation, intense multitasking), your brain burns through its catecholamine stores faster than usual. Tyrosine provides the raw material to replenish them.

Several studies have tested this in controlled settings. In one trial, military cadets exposed to a demanding week-long combat training course performed better on memory and tracking tasks when given tyrosine compared to placebo [3]. Another study found that tyrosine helped maintain cognitive performance during exposure to cold temperatures [4].

A 2015 study from Leiden University found that tyrosine supplementation improved cognitive flexibility, specifically the ability to switch between different tasks [5]. The researchers suggested tyrosine might help replenish dopamine in the prefrontal cortex during demanding cognitive work.

There’s a catch, though. Most of this research involves acute stress conditions: cold, sleep deprivation, high workload. For people sitting comfortably at their desks with adequate sleep, the benefits are less clear. Tyrosine doesn’t seem to enhance cognition beyond baseline in non-stressed individuals [6].

If you’re hoping tyrosine will make you smarter in general, the evidence doesn’t support that. But if you’re facing a genuinely stressful, demanding situation, there’s reasonable evidence it might help you maintain normal function.

2. Tyrosine and phenylketonuria (PKU)

Phenylketonuria is a genetic disorder where people can’t properly break down phenylalanine. The treatment involves strictly limiting phenylalanine in the diet. Since the body makes tyrosine from phenylalanine, people with PKU often have low tyrosine levels.

This seems like an obvious case for tyrosine supplementation. Surprisingly, the evidence is underwhelming. A Cochrane review looked at three randomised controlled trials with 56 PKU patients and found that while tyrosine supplements did raise blood tyrosine levels, there were no measurable improvements in intelligence, neuropsychological performance, growth, or quality of life [7].

The review concluded that routine tyrosine supplementation for PKU patients isn’t supported by current evidence, though some clinicians still use it for patients with very low tyrosine levels. More research is needed.

3. Tyrosine for depression

The logic here seems straightforward: dopamine and noradrenaline are involved in mood, tyrosine is a precursor to these neurotransmitters, so supplementing tyrosine should help depression. Unfortunately, the body doesn’t work quite that simply.

A randomised controlled trial in 65 patients with major depression found that oral tyrosine increased the excretion of a dopamine metabolite (MHPG), suggesting it was being converted to neurotransmitters. But here’s the disappointing part: there was no actual improvement in depressive symptoms compared to placebo [8].

The NHS lists tyrosine as one of the supplements sometimes marketed for mood support, but notes that there’s insufficient evidence to recommend it for treating depression [9]. If you’re dealing with depression, evidence-based treatments like cognitive behavioural therapy and antidepressant medications have much stronger research behind them.

4. Tyrosine and schizophrenia

Some researchers theorised that tyrosine might help schizophrenia symptoms by modulating dopamine levels. A placebo-controlled crossover trial tested this by adding tyrosine to standard antipsychotic medication (molindone).

The results were negative. Patients receiving tyrosine plus medication showed no improvement over those receiving medication alone on measures including the Brief Psychiatric Rating Scale and Clinical Global Impression scale [10].

Based on current evidence, tyrosine supplementation doesn’t appear helpful for schizophrenia.

5. Tyrosine for narcolepsy

Narcolepsy causes overwhelming daytime sleepiness and sudden sleep attacks. Since catecholamines are involved in arousal and wakefulness, researchers tested whether tyrosine might help.

A small randomised trial in 10 narcolepsy patients found that tyrosine improved some self-reported measures, including alertness and fatigue ratings [11]. However, objective measurements told a different story. There were no significant improvements in daytime sleepiness, sleep paralysis, cataplexy, or results from the Multiple Sleep Latency Test (an objective measure of sleepiness).

When subjective reports improve but objective measures don’t, that suggests a possible placebo effect. The authors concluded that tyrosine showed no clinically significant benefit for narcolepsy.

Side effects of tyrosine

For most healthy adults, tyrosine appears safe at typical supplement doses (usually 100-150 mg per kilogram of body weight, or roughly 500-2000 mg per day). Short-term studies using doses up to 150 mg/kg haven’t reported serious adverse effects [12].

That said, some people do experience mild side effects:

Nausea – the most commonly reported issue
Headache – particularly at higher doses
Heartburn – usually mild
Fatigue – somewhat paradoxically, given that tyrosine is supposed to boost alertness
Joint pain – reported occasionally

These side effects are generally mild and resolve when supplementation stops. There’s limited data on long-term safety because most studies only lasted a few weeks.

Who should avoid tyrosine (6 contraindications)

1. People with tyrosinaemia

Tyrosinaemia is a rare inherited disorder where the body can’t properly break down tyrosine. Taking additional tyrosine could cause it to accumulate to dangerous levels, potentially damaging the eyes, skin, liver, and kidneys. If you have this condition, tyrosine supplements are not appropriate.

2. Pregnant and breastfeeding women

There simply isn’t enough research to know whether tyrosine supplements are safe during pregnancy or breastfeeding. While tyrosine from food is fine, concentrated supplements are a different matter. The prudent choice is to avoid them unless specifically advised by a doctor.

3. People with kidney or liver disease

Your liver and kidneys are responsible for processing amino acids. If they’re not functioning well, concentrated amino acid supplements may be problematic. There’s no specific research on tyrosine in these populations, which is precisely why caution is warranted.

4. People taking thyroid medication or with hyperthyroidism

Tyrosine is a building block for thyroid hormones. If you’re already taking thyroid hormone medication (like levothyroxine) or have an overactive thyroid, adding tyrosine could theoretically push thyroid hormone levels higher. This could cause symptoms like rapid heartbeat, anxiety, weight loss, and heat intolerance.

If you have any thyroid condition, discuss tyrosine supplementation with your doctor before trying it.

5. People taking levodopa for Parkinson’s disease

Levodopa (L-DOPA) is the primary medication for Parkinson’s disease. Both tyrosine and levodopa compete for the same transport system to cross the blood-brain barrier. Taking tyrosine might reduce how much levodopa reaches your brain, potentially making your medication less effective [13].

If you’re on levodopa, don’t take tyrosine supplements without consulting your neurologist.

6. People taking monoamine oxidase inhibitors (MAOIs)

MAOIs are a class of antidepressant that blocks the enzyme responsible for breaking down certain neurotransmitters. When taking an MAOI, foods and supplements that increase tyramine or catecholamine precursors can cause dangerous spikes in blood pressure.

Tyrosine itself isn’t the same as tyramine, but it can increase catecholamine production. If you’re taking an MAOI (such as phenelzine, tranylcypromine, or selegiline), avoid tyrosine supplements unless your prescriber has specifically cleared it.

Practical considerations

If you’re considering tyrosine, here are some things worth knowing:

Timing matters. Most studies gave tyrosine about 30-60 minutes before the stressful task. Taking it with a high-protein meal may reduce absorption because tyrosine competes with other amino acids for transport.

Food sources are substantial. A 100g serving of hard cheese contains roughly 1.5g of tyrosine. A chicken breast has about 1.2g. If you eat adequate protein, you’re likely getting plenty of tyrosine already.

It’s not a nootropic miracle. Despite marketing claims, tyrosine doesn’t appear to enhance cognitive function beyond normal levels. Its benefit seems limited to preventing decline during acute stress.

Individual responses vary. Some people report noticeable effects; others notice nothing. This is true for most supplements.

If you’re interested in supplements for cognitive function and stress support, you might find these articles useful:

L-theanine benefits and side effects – an amino acid from tea that may promote calm alertness
Caffeine benefits and side effects – the world’s most widely used stimulant
Vitamin B complex benefits – B vitamins are involved in neurotransmitter synthesis

For those interested in thyroid health, amino acids, and metabolism:

Ginseng benefits and side effects – a traditional adaptogen
Taurine benefits and side effects – another amino acid with various proposed benefits

References

Fernstrom JD, Fernstrom MH. Tyrosine, phenylalanine, and catecholamine synthesis and function in the brain. J Nutr. 2007;137(6 Suppl 1):1539S-1547S. PubMed
Magnusson I, et al. N-acetyl-L-tyrosine and N-acetyl-L-cysteine as tyrosine and cysteine precursors during intravenous infusion in humans. Metabolism. 1989;38(10):957-961. PubMed
Deijen JB, et al. Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course. Brain Res Bull. 1999;48(2):203-209. PubMed
Mahoney CR, et al. Tyrosine supplementation mitigates working memory decrements during cold exposure. Physiol Behav. 2007;92(4):575-582. PubMed
Steenbergen L, et al. Tyrosine promotes cognitive flexibility: evidence from proactive vs. reactive control during task switching performance. Neuropsychologia. 2015;69:50-55. PubMed
Hase A, et al. Behavioural effects of tyrosine intake in healthy human adults: a systematic review. Neurosci Biobehav Rev. 2015;56:176-185. PubMed
Webster D, Wildgoose J. Tyrosine supplementation for phenylketonuria. Cochrane Database Syst Rev. 2013;(6):CD001507. PubMed
Gelenberg AJ, et al. Tyrosine for depression: a double-blind trial. J Affect Disord. 1990;19(2):125-132. PubMed
NHS. Vitamins, supplements and nutrition in pregnancy. NHS website
Deutsch SI, et al. L-tyrosine pharmacotherapy of schizophrenia: preliminary data. Clin Neuropharmacol. 1994;17(1):53-62. PubMed
Elwes RD, et al. Treatment of narcolepsy with L-tyrosine: double-blind placebo-controlled trial. Lancet. 1989;2(8671):1067-1069. PubMed
Jongkees BJ, et al. Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands: a review. J Psychiatr Res. 2015;70:50-57. PubMed
Mayo Clinic. L-tyrosine. Mayo Clinic website