L-tyrosine

L-Tyrosine: A Comprehensive Reference

1. Identity and Chemical Characterization

Names and Classification

L-Tyrosine (symbol Tyr or Y), also systematically named 4-hydroxyphenylalanine, is one of the 20 standard amino acids used by cells to synthesize proteins. It is classified as a conditionally essential amino acid with a polar side group. The full chemical name is 2-amino-3-(4-hydroxyphenyl)propanoic acid, making it a polar aromatic α-amino acid containing a phenolic hydroxyl group. Its molecular formula is C₉H₁₁NO₃, and it carries the CAS registry number 60-18-4.

In addition to the common amino acid L-tyrosine, which is the para isomer (para-tyr or 4-hydroxyphenylalanine), there are two additional regioisomers — meta-tyrosine (3-hydroxyphenylalanine) and ortho-tyrosine (2-hydroxyphenylalanine) — that occur in nature. The m-tyr and o-tyr isomers, which are rare, arise through non-enzymatic free-radical hydroxylation of phenylalanine under conditions of oxidative stress. Only the para-L form is the physiologically dominant species incorporated into human proteins and used as a neurotransmitter precursor.

Conditional Essentiality

L-Tyrosine is a nonessential amino acid, meaning that it is manufactured in the human body and does not need to be supplied in the diet; however, under certain physiological conditions it may need to be supplemented. L-Tyrosine is an aromatic amino acid required for protein synthesis in all organisms, but synthesized de novo in plants and microbes; in animals, tyrosine must be acquired through the diet or produced from L-phenylalanine by phenylalanine hydroxylase. It is considered an essential nutrient for people with phenylketonuria who lack the enzyme phenylalanine hydroxylase and are unable to convert phenylalanine into tyrosine.

Discovery and Etymology

The word "tyrosine" is from the Greek tyrós, meaning "cheese," as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese. E. Abderhalden and Y. Teruuchi, also in Germany, isolated it from silk waste in 1906.

2. Natural Sources and Dietary Occurrence

Food Sources

Tyrosine, which can also be synthesized in the body from phenylalanine, is found in many high-protein food products such as meat, fish, cheese, cottage cheese, milk, yogurt, peanuts, almonds, pumpkin seeds, sesame seeds, soy protein, and lima beans. The white of an egg has about 250 mg per egg, while beef, lamb, pork, tuna, salmon, chicken, and turkey contain about 500–1000 mg per 3 ounces (85 g) portion.

Dietary Reference Values

The Food and Nutrition Board of the U.S. Institute of Medicine set Recommended Dietary Allowances for essential amino acids in 2002; for phenylalanine plus tyrosine combined, the figure for adults 19 years and older is 33 mg/kg body weight per day. Because tyrosine is produced endogenously from the essential amino acid phenylalanine, dietary reference values for both are typically reported together rather than separately.

Biosynthesis in Plants and Microbes

Tyrosine serves as the precursor to numerous plant natural products with diverse functions, such as electron carriers (e.g., plastoquinone and ubiquinone), defense compounds (e.g., dhurrin and rosmarinic acid), and pollinator-attraction pigments (e.g., betalains). In plants, the amino acid is an electron donor in the process of photosynthesis.

3. Manufacturing and Commercial Forms

Supplement Preparations

L-Tyrosine is used in pharmaceuticals, dietary supplements, and food additives. Two methods were formerly used to manufacture it: the first involves extraction from protein hydrolysates using a chemical approach; the second utilizes enzymatic synthesis from phenolics, pyruvate, and ammonia through the use of tyrosine phenol-lyase. Advances in genetic engineering and the advent of industrial fermentation have shifted the synthesis of L-tyrosine to the use of engineered strains of E. coli.

The two principal oral supplement forms are free-form L-Tyrosine (the unmodified amino acid, available as capsules, tablets, or powder) and N-Acetyl L-Tyrosine (NALT). NALT is a synthetically modified form of L-Tyrosine in which an acetyl group is attached to the nitrogen atom of the molecule; this alteration is primarily made to change the physical properties of the compound, dramatically increasing its water solubility, as L-Tyrosine itself is not very soluble. NALT's enhanced solubility makes it useful for applications like intravenous feeding where a compound must be fully dissolved.

Despite the theoretical appeal of NALT's solubility, the evidence for its superiority over free L-Tyrosine via oral supplementation is not borne out. While NALT's enhanced solubility makes it appealing for supplement formulation, studies show this does not automatically translate to superior bioavailability; for NALT to become biologically active, the acetyl group must first be cleaved off by enzymes in the body, and this deacetylation process is often inefficient. Research comparing the two forms indicates that oral L-Tyrosine supplementation reliably increases plasma tyrosine levels, while NALT has been shown to have a minimal or no effect on increasing these concentrations.

4. Traditional and Historical Use

Tyrosine was not used traditionally as an herbal remedy; modern research has highlighted tyrosine's role in neurotransmitter regulation, stress resilience, and cognitive performance. Because L-Tyrosine is an endogenous amino acid constituent of all dietary proteins — not an isolated botanical extract — it does not carry distinct ethno-botanical traditions in the sense of a discrete herbal medicine practice. Its historical relevance is instead biochemical: every culture that consumed protein-containing foods (meat, dairy, legumes) was consuming dietary tyrosine as an unremarkable constituent.

The modern era of targeted tyrosine supplementation began with systematic scientific investigation in the latter half of the twentieth century, largely driven by research into catecholamine metabolism and then by military-funded human performance research. One nutrient that was investigated as potentially preventing performance decrements caused by highly stressful environmental or operational conditions was tyrosine; this substance was studied as the precursor of several key brain neurotransmitters that may protect against severe mental fatigue associated with life-threatening stressors occurring in combat and certain critical military operations.

5. Key Biochemical Constituents and Mechanisms of Action

Catecholamine Biosynthesis Pathway

Tyrosine, a large neutral amino acid normally present in protein-containing foods, is the precursor of the catecholamine neurotransmitters dopamine (DA), norepinephrine (NE), and epinephrine.

The catecholamine metabolic pathway in vivo begins with L-phenylalanine, which is converted into L-tyrosine by the enzyme phenylalanine hydroxylase. L-tyrosine is then converted into the compound L-DOPA via tyrosine hydroxylase. L-DOPA is then decarboxylated via aromatic L-amino acid decarboxylase into dopamine, which later becomes noradrenaline via oxidation from dopamine-beta-hydroxylase, and is finally converted to adrenaline via phenylethanolamine-N-methyl-transferase.

A critical principle governing this pathway is that tyrosine availability is rate-limiting only under specific demand conditions: the availability of tyrosine is rate-limiting for the synthesis of its neurotransmitter products only when a higher than normal level of transmitter release by catecholaminergic neurons is occurring. When catecholamine-containing neurons are firing frequently and therefore releasing more transmitter, they may require more of the precursor tyrosine for transmitter synthesis. This explains why supplementation produces the most consistent functional effects specifically during conditions of acute stress or demand.

Thyroid Hormone Synthesis

The thyroid hormones triiodothyronine (T3) and thyroxine (T4) in the colloid of the thyroid are also derived from tyrosine. Iodination of tyrosine residues within thyroglobulin is the initial step in the biosynthesis of both T3 and T4, making adequate tyrosine availability a prerequisite for normal thyroid function.

Melanin Production

Tyrosine is the precursor to the pigment melanin. In addition to protein synthesis, tyrosine is used to synthesize melanin skin pigments. The enzyme tyrosinase catalyzes the initial hydroxylation and subsequent oxidation steps converting tyrosine to dopaquinone, which then polymerizes to melanin. This pathway is operative in melanocytes and is relevant both to normal pigmentation and to conditions that impair it.

Protein Structure and Cell Signaling

The body uses L-tyrosine to build proteins, many of which are involved in signal transduction. L-tyrosine is incorporated into proteins and other biologically important molecules such as neurotransmitters, hormones, pigment melanin, and coenzyme Q10. The hydroxyl group on the phenol ring of tyrosine residues within proteins serves as a substrate for tyrosine kinase-mediated phosphorylation, a cornerstone of intracellular signaling networks governing cell growth, differentiation, and immune responses.

6. Body Systems and Health Areas

Central Nervous System and Neurotransmitter Function

L-Tyrosine is an amino acid used as a precursor for the synthesis of the catecholamines dopamine and norepinephrine. These are depleted under stressful conditions, which can compromise cognitive function. L-Tyrosine supplementation may help alleviate acute stress-induced cognitive decline by restoring catecholamine levels in the brain.

Endocrine System

In the body, tyrosine plays a role in protein synthesis and is a precursor for the synthesis of catecholamines, thyroxine, and melanin. Its involvement in thyroid hormone synthesis makes it relevant to hypothalamic-pituitary-thyroid axis physiology; accordingly, supplementation in individuals already receiving thyroid hormone therapy requires consideration (see Section 9).

Skin and Pigmentation

The disorder phenylketonuria is characterized by both substrate toxicity and a deficiency of downstream products, including catecholamine neurotransmitters, melanin, and other tyrosine-derived compounds. Tyrosine deficiency secondary to PKU is associated with hypopigmentation, illustrating the skin and hair pigmentation system as a major end-organ for tyrosine metabolism.

Metabolic and Genetic Disorders

PKU results from a deficiency of phenylalanine hydroxylase (PAH), the rate-limiting hepatic enzyme that converts phenylalanine to tyrosine and requires BH4, molecular oxygen, and iron as cofactors. Loss of PAH activity due to biallelic pathogenic variants impairs phenylalanine metabolism, leading to the accumulation of phenylalanine and its toxic metabolites, along with a relative tyrosine deficiency.

7. Scientific Evidence by Area of Use

7.1 Cognitive Performance Under Acute Stress

This is the most extensively studied area for L-tyrosine supplementation and the domain in which the most consistent positive signals have been reported.

A systematic review published in Military Medicine (2015) used the Rapid Evidence Assessment of the Literature (REAL) process to examine the available RCT and controlled clinical trial evidence. Ten randomized controlled trials and four controlled clinical trials met the inclusion criteria. On the basis of the available evidence, no recommendation could be made for the effect of tyrosine on physical performance under stressful physical conditions; however, a weak recommendation in favor of tyrosine was made for cognitive stress, as all studies showed a positive effect. The review concluded that the available evidence is insufficient to make confident recommendations on the effectiveness of tyrosine for mitigating stress effects on physical or cognitive performance, but that tyrosine may benefit cognitive performance and is worthy of further study.

A narrative review in the Journal of Psychiatric Research (Jongkees et al., 2015) covering both clinical and healthy populations concluded similarly: given the right circumstances, tyrosine supplementation can enhance dopamine and norepinephrine levels in the brain, and this possibility has led numerous studies to investigate whether administration of tyrosine can positively influence cognitive or behavioral performance relying on catecholamine function; however, reports on the effectiveness of tyrosine supplementation have varied greatly, with some studies showing a marked positive effect whereas others report no significant changes.

Cold Stress

Young men who were exposed to cold and hypoxia exhibited fewer stress symptoms — such as headache, tension, and fatigue — and showed fewer psychomotor impairments after being supplemented with 100 mg/kg tyrosine. A study by Mahoney and colleagues (2007, Physiology and Behavior) is among those cited in the systematic literature as demonstrating that tyrosine supplementation mitigates working memory decrements during cold exposure.

Sleep Deprivation

Supplementation with L-tyrosine has been shown to improve aspects of working memory or cognitive processing in sleep-deprived conditions. Data from Magill et al. (2003, Nutritional Neuroscience) demonstrated favorable effects among healthy young men under sleep-deprived conditions.

Military and Combat Training

A study reported in Brain Research Bulletin (1999) used military academy cadets undergoing a combat training course involving sustained operations, physical demands, and sleep deprivation. The study was designed to determine whether the administration of L-tyrosine would be effective in reducing the effects of "real-life" stress, and was carried out with cadets who had to complete a combat training course; as this course involved psychologically as well as physically highly demanding conditions including sustained operations and sleep loss, it was considered an appropriate environment to study the stress-reducing properties of L-tyrosine, with a specific focus on cognitive functioning after stress induction.

A 2024 pre-registered randomized clinical trial published in Stress (Taylor & Francis) examined L-tyrosine ingestion during a simulated active-shooter training drill in tactical personnel. Ingestion of L-tyrosine did not impact markers of stress; however, the L-tyrosine treatment demonstrated significantly lower missed responses compared to the placebo treatment group during the Stroop cognitive challenge.

Exercise Heat Stress

Not all stressor paradigms show benefit. A study in humans examining a single dose of 150 mg/kg L-tyrosine body mass during military-style exercise in the heat found that despite marked elevations in serum tyrosine concentration, ingestion of tyrosine did not influence cognitive function or physical performance during exercise heat stress. Specifically, exercise heat stress impaired some aspects of cognitive function; however, tyrosine did not alleviate these decrements (P > 0.05), and no difference was observed in any physiological variable or time trial completion time between the tyrosine and placebo conditions.

Working Memory Gating

A PMC-indexed study (Bloemendaal et al., 2020, Journal of Cognitive Neuroscience; PMC7266860) administered L-tyrosine to healthy young adults performing a reference-back working memory paradigm. The study determined the effects of dopamine's precursor L-tyrosine on working memory in healthy young adults, while isolating cognitive performance related to updating, opening, and closing the gate to working memory. More recent data suggest that the cognitive enhancing effects of L-tyrosine are likely attributed to dopamine activity and are perhaps age-dependent, but more data are needed to support this conclusion.

Overall Evidence Characterization — Cognitive Performance

The weight of evidence supports a context-dependent benefit: the potential of using tyrosine supplementation to treat clinical disorders seems limited and its benefits are likely determined by the presence and extent of impaired neurotransmitter function and synthesis; likewise, the potential of tyrosine supplementation for enhancing physical exercise seems minimal. The most consistent evidence is for attenuation of cognitive decrements during acute stressors (cold, sleep deprivation, demanding military tasks), rather than enhancement of performance in non-stressed, well-rested individuals.

7.2 Phenylketonuria (PKU)

Phenylketonuria is an autosomal recessive disorder of phenylalanine metabolism in which especially high phenylalanine concentrations cause brain dysfunction; if untreated, this brain dysfunction results in severe intellectual disability, epilepsy, and behavioral problems. Since loss of PAH activity leads to a relative tyrosine deficiency, L-tyrosine supplementation has been investigated as a means of correcting this deficiency.

Despite the rational biochemical basis, clinical evidence for benefit is not established. There is no evidence to support the use of tyrosine in the metabolic genetic disorder phenylketonuria. Whether supplementing L-tyrosine can help with PKU symptoms is yet to be determined, as studies show no improvement when L-tyrosine supplements were taken. Dietary supplementation with large neutral amino acids including tyrosine and tryptophan has been recommended for individuals with chronically elevated blood phenylalanine in an attempt to restore amino acid and monoamine homeostasis in the brain, but the clinical effectiveness of this strategy remains contested and under investigation.

7.3 Depression and Mood

The rationale for investigating tyrosine in depression is that catecholamine depletion is implicated in some depressive presentations. Tyrosine levels are occasionally low in depressed people. However, evidence for clinical antidepressant efficacy is very limited. A 2016 study found that L-tyrosine might be beneficial for treating depression; however, researchers conducted the study on animals and stated that the antidepressant properties of L-tyrosine need further investigation. In clinical depression, which involves complex dysregulation beyond catecholamine levels, the evidence does not support tyrosine as a primary intervention.

7.4 Attention-Deficit/Hyperactivity Disorder (ADHD)

The dopaminergic and noradrenergic deficits associated with ADHD have prompted interest in tyrosine as a nutritional support. However, the clinical evidence does not currently support this application. No evidence supports the use of L-tyrosine to treat ADHD in adults or children; more research is required to determine if it is an effective treatment for the condition. Some experts thought that low levels of tyrosine in the body might be related to ADHD, which supported the use of L-tyrosine as a possible treatment; however, a 2016 study revealed that children with ADHD had normal levels of tyrosine and other amino acids in their blood. The existing evidence does not support the use or benefits of tyrosine for ADHD specifically.

7.5 Parkinson's Disease and Orthostatic Hypotension

Individuals with Parkinson's disease can suffer from orthostatic hypotension resulting from reduced levels of norepinephrine, which inhibits the sympathetic nervous system; levodopa reduces norepinephrine levels even further, leading to a greater decrease in blood pressure and increased orthostatic hypotension. Tyrosine is a nonessential amino acid that is the major precursor to norepinephrine, and reduced levels of tyrosine have been shown after administration of L-dopa.

A randomized, double-blind, placebo-controlled trial (DiFrancisco-Donoghue et al., 2018; PMC6183247) tested L-tyrosine in 36 subjects with PD and orthostatic hypotension who were receiving L-dopa medication. The study tested the effects of supplementing L-tyrosine on blood pressure, plasma tyrosine, norepinephrine levels, and autonomic responses to exercise in PD; 36 subjects with PD receiving L-dopa medication who suffered from orthostatic hypotension participated, and random assignment was to a placebo group or L-tyrosine 1,000 mg (500 mg twice daily) group for 7 days. Tyrosine was well tolerated in all subjects with no adverse reactions reported; however, while the study demonstrated a significant increase in plasma levels of tyrosine in the tyrosine group, it failed to show any effect on blood pressure using an orthostatic hypotension test. This was a single-centre trial of short duration; findings are preliminary.

7.6 Physical Exercise Performance

Clinical trial data for enhancement of sports performance is limited and does not support tyrosine supplementation. The systematic review published in Military Medicine (2015) similarly found that on the basis of the available evidence, no recommendation could be made for the effect of tyrosine on physical performance under stressful physical conditions.

8. Dosage Forms and Dosages Reported in Studies

L-Tyrosine is commercially available as free-form powder, capsules, and tablets, as well as in the derivatized N-acetyl form (NALT). The following dosage figures are drawn directly from cited human study sources.

• Studies in humans showing the most anti-stress promise for acute supplemental L-Tyrosine use a dosage range of 100–150 mg/kg of bodyweight taken 60 minutes before exercise; this is a dosage range of 9–13.5 g for a 200 lb person and 7–10 g for a 150 lb person.
• Limited clinical studies use 100 to 150 mg/kg per day; manufacturers commonly recommend 500 to 1,500 mg/day, and dosages of more than 12 g/day are not recommended.
• Anecdotally, L-Tyrosine tends to be taken in doses of 500–2,000 mg approximately 30–60 minutes before any acute stressor.
• In the Parkinson's disease orthostatic hypotension RCT, the active arm received L-tyrosine 1,000 mg per day (500 mg twice daily) for 7 days.
• In a small pharmacokinetic study comparing tyrosine loading in adolescents with anorexia nervosa to healthy controls, supplementation with L-tyrosine 2.5 g twice daily for 12 weeks was used.
• Single-dose pharmacokinetic data in healthy controls showed a percentage change in tyrosine levels ranging from 152% to 194%; overall, tyrosine levels peaked at 2 to 3 hours and approached baseline at 8 hours.
• If using higher doses and experiencing digestive issues, the dose may be split into two portions separated by half an hour (30 and 60 minutes prior to acute stress).

9. Safety Considerations and Drug Interactions

General Safety Profile

Tyrosine supplementation is generally safe and well tolerated; however, thorough safety analyses are needed. L-tyrosine supplements are recognized as generally safe by the U.S. Food and Drug Administration (FDA), but they may cause interactions with certain medications.

The effect of excessive intake of tyrosine has only been studied in rats; in one rat study, tyrosine at a human-equivalent dose of around 320 mg/kg of body weight daily for 13 weeks had negative effects on blood, liver, and kidney parameters. The relevance in humans is unclear.

Monoamine Oxidase Inhibitors (MAOIs)

Tyrosine is contraindicated with MAOIs such as isocarboxazid, phenelzine, tranylcypromine, and selegiline. Monoamine oxidase is the enzyme responsible for the breakdown and inactivation of the catecholamines; a buildup of the catecholamines — including tyramine, which can be found in certain foods and formed from exogenous tyrosine in the gut by certain bacteria — can result in dangerous increases in blood pressure.

Thyroid Hormone Medications

Tyrosine is a precursor to thyroid hormones and might boost levels of thyroid hormone medications like levothyroxine and liothyronine. Tyrosine is contraindicated in hyperthyroidism or Graves' disease because it may increase levels of thyroid hormone. Caution is warranted in people with thyroid conditions.

Levodopa (L-DOPA)

L-tyrosine may also interact with levodopa (L-dopa). Because both L-tyrosine and L-DOPA compete for the same large neutral amino acid transporter (LAT1) at the blood-brain barrier, concurrent ingestion of L-tyrosine with levodopa could in theory reduce the drug's central uptake. This interaction was among the motivating rationale for the Parkinson's disease orthostatic hypotension trial described above.

Pregnancy and Lactation

Tyrosine supplemented at high doses may not be safe during pregnancy and lactation, and avoidance is warranted; research is lacking.

Renal Disease

Any person losing large amounts of protein, such as those with some kidney diseases, may be deficient in several amino acids, including tyrosine. Conversely, individuals with significantly impaired renal function require caution with high amino acid loads generally, as amino acid metabolism and nitrogen excretion depend on adequate kidney function.

Nemaline Myopathy — A Cautionary Example of Preliminary Data

Case reports and a small uncontrolled trial suggested potential benefit of L-tyrosine in nemaline myopathy (NM). A small trial of 5 genetically undefined NM patients (4 infants, 1 adolescent with childhood onset) received between 250 to 3,000 mg/day of powdered or capsule L-tyrosine for 2 to 5 months; within 72 hours all infants displayed initial improvements in salivation, skeletal muscle strength, and energy levels. However, subsequent controlled animal model research did not confirm therapeutic efficacy, illustrating the limitations of open-label anecdotal reports and the need for rigorous trials before clinical conclusions can be drawn.

10. Summary of Evidence Quality

• Cognitive performance under acute stress (cold, sleep deprivation, demanding military tasks): Moderate to weak positive evidence from multiple small RCTs and controlled trials. A systematic review made only a "weak recommendation" in favor of benefit for cognitive stress. Evidence is not sufficient to make confident recommendations, per the review authors.
• Phenylketonuria: No clinical evidence of benefit despite clear biochemical rationale; current studies do not support tyrosine supplementation for improving PKU outcomes.
• Depression: Evidence limited to animal models; no quality human RCT evidence supports tyrosine as an antidepressant.
• ADHD: No clinical evidence of benefit; children with ADHD have been shown to have normal circulating tyrosine levels.
• Parkinson's disease / orthostatic hypotension: A single short-duration RCT showed no effect on blood pressure despite elevation of plasma tyrosine.
• Physical exercise performance: Not supported by available clinical trial data.
• Safety (general): Generally considered safe and well tolerated at commonly used doses; formal long-term safety analyses in humans are lacking. Drug interactions with MAOIs, thyroid hormones, and levodopa are clinically significant.

References

• American Chemical Society — L-Tyrosine Molecule of the Week
• Wikipedia — Tyrosine
• PubChem — L-Tyrosine (CID 6057)
• NIH/NCBI Bookshelf — Tyrosine and Stress: Human and Animal Studies
• PMC — Conserved Molecular Mechanism of TyrA Dehydrogenase (Schenck et al., 2017)
• Examine.com — L-Tyrosine: Benefits, Dosage, and Side Effects
• Examine.com — Research Breakdown on L-Tyrosine
• Military Medicine — Tyrosine for Mitigating Stress and Enhancing Performance in Healthy Adult Humans: A Rapid Evidence Assessment (2015)
• Journal of Psychiatric Research — Effect of Tyrosine Supplementation on Clinical and Healthy Populations Under Stress or Cognitive Demands (Jongkees et al., 2015)
• PubMed — Tyrosine Ingestion and Its Effects on Cognitive and Physical Performance in the Heat
• Brain Research Bulletin — Tyrosine Improves Cognitive Performance and Reduces Blood Pressure in Cadets After One Week of a Combat Training Course (1999)
• Stress (Taylor & Francis) — Impact of L-theanine and L-tyrosine on Markers of Stress and Cognitive Performance (2024)
• PMC — Effects of Tyrosine on Parkinson's Disease: A Randomized, Double-Blind, Placebo-Controlled Trial
• PMC — Phenylketonuria (Review, 2021)
• NIH/NCBI StatPearls — Phenylketonuria (PKU)
• PMC — Pharmacologic Inhibition of L-Tyrosine Degradation Ameliorates Cerebral Dopamine Deficiency in Murine PKU
• PMC — Baseline-Dependent Effect of Dopamine's Precursor L-Tyrosine on Working Memory Gating (Bloemendaal et al., 2020)
• Drugs.com — Tyrosine Uses, Benefits & Dosage (medically reviewed)
• Cleveland Clinic Health — Should You Try an L-Tyrosine Supplement?
• Medical News Today — L-Tyrosine and ADHD: Benefits, Side Effects, Dosage, and More
• PsychCentral — Is L-Tyrosine the New Adderall for ADHD?
• ScienceInsights — N-Acetyl L-Tyrosine vs L-Tyrosine: What's the Difference?
• Journal of Renal Nutrition — The Metabolic Conversion of Phenylalanine into Tyrosine in the Human Kidney (2002)
• ClinicalTrials.gov — Effect of Tyrosine Supplementation on Cognitive Performance and Mood During Military Stress (NCT01913925)
• bioRxiv — L-Tyrosine Supplementation and Nemaline Myopathy Models