Tyrosine

Tyrosine is a conditionally essential amino acid that the body makes from phenylalanine, and the most direct building block for dopamine, noradrenaline, adrenaline, thyroid hormones, and melanin. Because it enters the catecholamine pathway one step later than phenylalanine, it’s the more direct precursor supplement, and it has a clearer evidence base than most amino acid supplements — in one particular context: mental performance under acute stress. Studies, many of them military, have found that tyrosine helps preserve working memory, attention, and mental flexibility during sleep deprivation, cold exposure, simulated high altitude, and demanding training — situations that heavily tax the brain’s catecholamine systems. In rested, unstressed people, the effects are weaker and less consistent, and there’s little evidence that tyrosine improves physical performance.

Classification

• Type: Conditionally essential amino acid — made from phenylalanine by phenylalanine hydroxylase; becomes essential when that enzyme doesn’t work (as in PKU)
• Side chain: A phenol group — a benzene ring carrying a hydroxyl group, which is what distinguishes tyrosine from phenylalanine. In thyroid hormones, iodine atoms attach to the ring on either side of this hydroxyl group
• Metabolism: Both glucogenic and ketogenic — tyrosine is broken down into fumarate, which can be used to make glucose, and acetoacetate, a ketone body
• Brain entry: Enters the brain through the LAT1 transporter, competing with phenylalanine, tryptophan, and the three BCAAs

Key Mechanisms

The catecholamine pathway:

Tyrosine is the starting point of the catecholamine pathway — phenylalanine must first be converted into tyrosine before it can enter:

1. Tyrosine → L-DOPA: tyrosine hydroxylase, the rate-limiting enzyme, which needs tetrahydrobiopterin (BH4), iron, and oxygen
2. L-DOPA → Dopamine: aromatic L-amino acid decarboxylase, which needs vitamin B6 (as PLP)
3. Dopamine → Noradrenaline: dopamine beta-hydroxylase, which needs vitamin C and copper
4. Noradrenaline → Adrenaline: phenylethanolamine N-methyltransferase, which uses SAM made from methionine

Dopamine supports motivation, reward, goal-directed behavior, working memory, and movement — the loss of dopamine-producing neurons causes Parkinson’s disease. Noradrenaline drives alertness, focused attention, and the fight-or-flight response. Adrenaline drives the acute stress and exercise response — releasing glucose and fat for fuel, raising heart rate and output, and opening the airways.

Why tyrosine rather than phenylalanine: phenylalanine has to be converted into tyrosine first, while tyrosine enters the pathway directly — so tyrosine is the more direct supplement for supporting catecholamine production.

Why stress matters: normally, tyrosine hydroxylase has plenty of tyrosine to work with, so extra tyrosine changes little. But when catecholamine neurons fire intensely for long periods — during sleep deprivation, cold, low oxygen, or demanding mental work — the enzyme speeds up, and tyrosine supply may start to limit production. The leading explanation for tyrosine’s effects is that extra tyrosine helps the brain keep up its catecholamine supply in these situations, which fits the finding that benefits appear mainly under stress.

Thyroid hormones:

Thyroid hormones are built from tyrosine units in thyroglobulin, a large protein made by the thyroid gland:

1. The enzyme thyroid peroxidase attaches iodine to tyrosine units in thyroglobulin, forming:
   • Monoiodotyrosine (MIT) — one iodine atom
   • Diiodotyrosine (DIT) — two iodine atoms
2. Pairs of these join together:
   • MIT + DIT → T3 (triiodothyronine — three iodines; the active form)
   • DIT + DIT → T4 (thyroxine — four iodines; the main form released by the thyroid)
3. T4 is converted into active T3 in the body’s tissues by selenium-dependent deiodinase enzymes

Because thyroglobulin is a protein the body makes from its normal amino acid supply, tyrosine doesn’t limit thyroid hormone production in people eating enough protein — iodine is the nutrient that matters. There’s no evidence that tyrosine supplements improve thyroid function, despite their frequent inclusion in “thyroid support” products.

Melanin:

Tyrosine → L-DOPA → dopaquinone → (several steps) → melanin (via tyrosinase, a copper-dependent enzyme)

Melanin gives color to skin, hair, and eyes, in two main forms: eumelanin (brown-black) and pheomelanin (red-yellow). L-DOPA is an intermediate in both the melanin and dopamine pathways. A related dark pigment, neuromelanin, builds up in the dopamine-producing neurons of the substantia nigra (“black substance”) — the brain region whose neurons are lost in Parkinson’s disease.

Protein structure and cell signalling:

Tyrosine units in proteins are key “switch” sites. Receptor tyrosine kinases — including the insulin receptor and many growth factor receptors — attach phosphate groups to tyrosine units to pass on their signals, controlling cell growth, metabolism, and immune responses. These tyrosine units are built into the proteins themselves, so dietary tyrosine doesn’t influence this signalling.

Recommended Intake

Found In (per 100g)

Tyrosine is spread widely across animal and plant proteins, so any diet with enough protein provides plenty for catecholamine and thyroid hormone production. Dairy proteins are the richest as a share of protein (about 5.5%), because casein is especially rich in tyrosine, while most meat, fish, eggs, nuts, and seeds sit at about 3–4%, and legumes and almonds a little lower. Bananas, sometimes recommended as a tyrosine source, contain very little.

Tyramine: aged cheeses such as parmesan are also high in tyramine, a compound formed from tyrosine by bacteria during ageing and fermentation. Tyramine is also found in cured meats, soy sauce, and some fermented foods and drinks, and it’s the reason these foods are restricted for people taking certain antidepressants (see below).

Helps With

• Making dopamine — for motivation, reward, focus, and movement
• Making noradrenaline — for alertness, attention, and the stress response
• Making adrenaline — for the acute exercise and stress response
• Preserving mental performance during sleep deprivation, cold, low oxygen, and other acute stress
• Making thyroid hormones, as part of the protein thyroglobulin
• Making melanin, for pigmentation
• Cell signalling, as switch sites in proteins such as the insulin receptor

Tyrosine for Athletes and Active People

Tyrosine has one of the clearer evidence bases among amino acid supplements, but it’s specific: preserving mental performance under acute stress, rather than improving physical performance.

Mental performance under stress — the main evidence:

• Sleep deprivation: in a study of people kept awake overnight, about 150mg per kg of tyrosine reduced the decline in performance on demanding mental tasks for roughly three hours compared with placebo
• Cold: in military studies, tyrosine reduced cold-related declines in working memory
• Cold and altitude combined: in a study simulating cold, high-altitude conditions, tyrosine reduced symptoms and declines in mental performance
• Demanding training: military cadets taking a tyrosine-rich drink (2g a day) during a week of intense combat training had better memory and tracking performance than those on placebo

Reviews conclude that tyrosine can help counter stress-related declines in working memory and mental flexibility, although most studies are small, used large doses, and tested specific military or laboratory stressors.

Physical performance: evidence is much weaker. One study found that tyrosine extended exercise capacity in the heat, but later studies, including one testing time-trial performance in the heat, found no effect. There’s no good evidence that tyrosine improves strength, power, or endurance in normal conditions.

Situations where it might help athletes:

• Competing or training after significant sleep loss, such as after long-haul travel
• Mentally demanding sessions or competitions in cold conditions
• High-altitude training or competition
• Long events where decision-making and focus matter, such as adventure racing or ultra-endurance events with little sleep

The rested athlete: in rested, well-fed athletes who aren’t under acute stress, tyrosine’s effects are weak and inconsistent. If the brain already has plenty of tyrosine, extra doesn’t meaningfully raise dopamine or noradrenaline.

Thyroid function in athletes: fatigue, feeling cold, slow recovery, and low motivation can reflect low thyroid hormone levels — but in athletes, the most common cause isn’t a lack of tyrosine. It’s low energy availability, part of relative energy deficiency in sport (RED-S): not eating enough to cover training lowers active thyroid hormone (T3). Eating enough, getting enough iodine, and seeing a doctor if symptoms persist are the right steps — tyrosine supplements won’t fix it.

Motivation and overtraining: overtraining is associated with low motivation and loss of enjoyment, and changes in dopamine signalling may play a part. There’s no evidence that tyrosine helps, though — the solution is rest, managing training load, adequate energy intake, and sleep.

Tyrosine Deficiency

In healthy adults eating enough protein: deficiency doesn’t occur — tyrosine comes from food and from phenylalanine.

Phenylketonuria (PKU): when phenylalanine can’t be converted into tyrosine, tyrosine becomes essential, so people with PKU get tyrosine from their special protein formulas. The fair skin and hair typical of untreated PKU reflect reduced melanin production. See our phenylalanine page for more on PKU.

Inherited BH4 deficiencies: these rare disorders affect the cofactor needed by tyrosine hydroxylase (and the enzymes that make serotonin), so the brain can’t make enough dopamine or serotonin despite plenty of tyrosine. They’re picked up by the same newborn screening as PKU and treated with BH4, L-DOPA, and 5-HTP.

Signs of severe protein deficiency include poor growth, muscle loss, and fatigue; specific symptoms from low tyrosine alone are rarely seen outside these disorders.

Excessive Doses of Tyrosine

No formal upper limit has been set. Doses of a few grams are generally well tolerated, and research doses of up to about 150mg per kg have been used in short-term studies, with side effects such as nausea, headache, and heartburn in some people.

Possible effects at high doses: nausea and digestive upset, headache, feeling jittery or anxious, and difficulty sleeping if taken late in the day.

MAO inhibitors — the most important safety concern: monoamine oxidase (MAO) breaks down catecholamines and tyramine. MAO inhibitor medicines — such as phenelzine and tranylcypromine for depression, and selegiline and rasagiline for Parkinson’s disease — block this breakdown. Combined with tyramine-rich foods, older MAO inhibitors can cause a dangerous spike in blood pressure (the “cheese reaction”). People taking MAO inhibitors should avoid tyrosine supplements unless their doctor approves.

Other cautions: people taking levodopa for Parkinson’s disease should know that tyrosine competes with it for transport into the brain. People with an overactive thyroid, or who take thyroid hormone medicine, should check with their doctor before taking tyrosine supplements.

Tyrosinemia: in rare inherited disorders of tyrosine breakdown, tyrosine or its breakdown products build up. The most serious form, tyrosinemia type I, damages the liver and kidneys; it’s treated with the drug nitisinone and a diet low in tyrosine and phenylalanine.

Types and Forms

• L-Tyrosine (free form): the standard form and the one used in most studies; well absorbed.
• N-Acetyl-L-tyrosine (NALT): marketed as more bioavailable because it dissolves better in water. Its solubility is genuinely higher, but the body has to remove the acetyl group before it can use the tyrosine, and studies show much of it is excreted unchanged — so it raises blood tyrosine less effectively than plain L-tyrosine.
• D-Tyrosine: the mirror-image form; not used for catecholamine production and not sold as a supplement.

Which form for your goal:

How to Take Tyrosine

Timing: blood tyrosine peaks one to two hours after a dose, and most studies gave tyrosine about an hour before the stressful task or event.

Away from big protein meals: the BCAAs, phenylalanine, and tryptophan compete with tyrosine for entry into the brain, so taking it away from a large protein meal or a BCAA supplement may help more of it reach the brain.

Not late in the day: because it supports alertness-related neurotransmitters, tyrosine could interfere with sleep if taken in the evening.

Choose L-tyrosine over NALT: plain L-tyrosine raises blood tyrosine more effectively.

Check your medicines: avoid tyrosine supplements if you take MAO inhibitors, and talk to your doctor first if you take levodopa or thyroid medicine, or have high blood pressure.

Interactions

BH4 is needed by tyrosine hydroxylase, the rate-limiting enzyme for catecholamine production. Vitamin B6 is needed to convert L-DOPA into dopamine, and vitamin C and copper to convert dopamine into noradrenaline. SAM, made from methionine, is needed to convert noradrenaline into adrenaline. Iodine and selenium are needed to make and activate thyroid hormones. MAO inhibitors can interact dangerously with tyrosine supplements and tyramine-rich foods. The BCAAs, phenylalanine, and tryptophan compete with tyrosine for entry into the brain, and tyrosine competes with levodopa.

Synergy

• Works with phenylalanine, its precursor — phenylalanine supplies tyrosine, and dietary tyrosine reduces the need for conversion.
• Works with iodine and selenium in thyroid hormone production — tyrosine provides the structure, iodine is attached to it, and selenium-dependent enzymes activate T4 into T3.
• Works with copper and vitamin C in making noradrenaline.
• Works with methionine (as SAM) in making adrenaline.
• Shares the L-DOPA step between melanin and dopamine production, with copper-dependent enzymes in both pathways.

Antagonistic Interactions

• The BCAAs, phenylalanine, and tryptophan compete with tyrosine for brain entry.
• MAO inhibitors combined with tyrosine supplements or tyramine-rich foods can cause dangerous rises in blood pressure.
• Tyrosine competes with levodopa for transport into the brain.
• High doses can cause jitteriness, headache, and sleep problems.

Food values: USDA FoodData Central, SR Legacy — parmesan, hard (FDC ID 170848); cheddar, sharp, sliced (170899)*; pumpkin and squash seed kernels, dried (170556)*; peanuts, raw (172430)*; chicken breast, roasted (171477); turkey breast, roasted (174516); pork top loin chop, broiled (167841); yellowfin tuna, cooked (172006); sardines, canned in oil (175139); ground beef, 80% lean, cooked (171797); Atlantic salmon, farmed, cooked (175168); tofu, firm, calcium-set (172475); cottage cheese, low-fat, 2% (172182)*; egg, hard-boiled (173424); almonds (170567)*; oats, dry (173904); black beans, cooked (173735); lentils, cooked (172421); chickpeas, cooked (173757); white rice, cooked (168878); banana, raw (173944)*. * SR Legacy values used as fill-ins for the Foundation Foods entries for cheddar (328637), pumpkin seeds (2515380), peanuts (2515376), cottage cheese (328841), almonds (2346393), and banana (1105314), whose amino acid data aren’t included in our tracker. Tyrosine as % of protein is calculated from the same USDA records.