Research
L-Tyrosine
27 peer-reviewed studies curated from PubMed and Semantic Scholar.
Studies
Sorted by quality and recency
Intralymphatic immunotherapy with tyrosine-adsorbed allergens: a double-blind, placebo-controlled trial.
This randomized, double-blind, placebo-controlled trial evaluated the efficacy and safety of intralymphatic immunotherapy with L-tyrosine-adsorbed allergen extracts in patients with allergic rhinitis. The study found that while ILAIT reduced daily medication use and skin reactivity to allergens, overall symptom scores and other measures were similar between treatment and control groups. Intralymphatic injection was more painful than venous puncture, with pain at the injection site and systemic adverse events reported.
[Validity of the use of L-Tyrosine to enhance fertility of female domestic animals. A study on the evidence from the literature].
Systematic and statistical analysis of literature on the use of L-Tyrosine to enhance fertility in female domestic animals. The analysis found methodical deficits and inconsistent findings across studies, indicating a need for further research on its effectiveness and dosage.
Effects of L-Tyrosine Ingestion on Endurance Performance in Mentally Fatigued Cyclists.
This study investigated the effects of L-tyrosine supplementation on endurance performance in mentally fatigued cyclists. Twelve recreational cyclists completed cycling tests under L-tyrosine and placebo conditions. L-tyrosine ingestion increased time to exhaustion by approximately 16% and reduced the rate of perceived exertion slope, suggesting moderate performance benefits.
The catecholamine precursor Tyrosine reduces autonomic arousal and decreases decision thresholds in reinforcement learning and temporal discounting.
This study investigated the effects of a single dose of tyrosine (2g) versus placebo on cognitive performance in 28 healthy male participants using a double-blind, placebo-controlled, within-subject design. Tyrosine supplementation reduced reaction times without deteriorating task performance, linked to attenuated decision thresholds and increased model-based control. Physiological monitoring showed reduced autonomic arousal, suggesting tyrosine impacts psychophysiological parameters.
Baseline-dependent effect of dopamine's precursor L-tyrosine on working memory gating but not updating.
Double-blind, placebo-controlled, within-subjects study of 45 healthy young adults examining the effects of 2.0 g L-tyrosine on working memory processes. L-tyrosine had a selective, baseline-dependent effect on gate opening in working memory, with low-performing subjects improving and high-performing subjects being impaired, indicating an inverted U-shaped relationship between dopamine and working memory.
Increased dopamine availability magnifies nicotine effects on cognitive control: A pilot study.
Pilot study testing the interaction between L-tyrosine and nicotine on cognitive control in 38 healthy non-smokers. L-tyrosine increased dopamine availability, magnifying nicotine's effects, improving cognitive flexibility but decreasing cognitive stability.
Oral L-Tyrosine Supplementation Improves Core Temperature Maintenance in Older Adults.
RCT with 18 participants (9 young, 9 older) testing oral L-tyrosine supplementation on core temperature maintenance during cold exposure. L-tyrosine improved cutaneous vasoconstriction and core temperature maintenance in older adults compared to placebo.
Effects of l-Tyrosine on working memory and inhibitory control are determined by DRD2 genotypes: A randomized controlled trial.
This double-blind, randomized, placebo-controlled trial investigated the effects of l-Tyrosine on working memory and inhibitory control, considering DRD2 genotypes. T/T homozygotes showed larger beneficial effects of TYR supplementation than C/C homozygotes, suggesting genetic differences in dopamine function may influence response to TYR as a cognitive enhancer.
Neurotransmitter-precursor-supplement intervention for detoxified heroin addicts.
Cluster-randomized placebo-controlled trial of 83 detoxified heroin addicts examining the effects of tyrosine, lecithin, L-glutamine, and 5-HTP on withdrawal syndromes and mental symptoms. The intervention group showed significant improvements in insomnia, withdrawal scores, and mood states compared to the control group.
A comparison of tyrosine against placebo, phentermine, caffeine, and D-amphetamine during sleep deprivation.
RCT comparing tyrosine, caffeine, phentermine, D-amphetamine, and placebo during sleep deprivation in 76 healthy males. Tyrosine had no significant effect on sleep parameters but stimulated prolactin release.
Effects of tyrosine, phentermine, caffeine D-amphetamine, and placebo on cognitive and motor performance deficits during sleep deprivation.
RCT comparing the effects of tyrosine, caffeine, phentermine, D-amphetamine, and placebo on cognitive and motor performance during sleep deprivation in healthy young men. Tyrosine improved performance on several cognitive and motor tests, though it was less effective than D-amphetamine.
A Double Blind, Randomized Cross-Over Trial of Tyrosine Treatment on Cognitive Function and Psychological Parameters in Severe Hospitalized Anorexia Nervosa Patients.
Double blind, randomized cross-over trial of L-tyrosine supplementation in 19 female hospitalized anorexia nervosa patients. Tyrosine shortened reaction time and test duration in memory tasks and improved depressive mood without side effects.
Effects of L-tyrosine and carbohydrate ingestion on endurance exercise performance.
RCT with nine competitive cyclists testing the effects of L-tyrosine and carbohydrate ingestion on endurance performance. Tyrosine ingestion did not enhance performance during a cycling time trial after 90 minutes of steady-state exercise.
L-tyrosine pharmacotherapy of schizophrenia: preliminary data.
A placebo-controlled, double-blind crossover study investigated L-tyrosine as an adjuvant to molindone in schizophrenia treatment. No significant improvement was found in psychiatric scales or neuropsychological performance, but L-tyrosine increased plasma levels and saccadic intrusions during smooth-pursuit eye movement tests.
Tyrosine for depression: a double-blind trial.
RCT comparing oral L-tyrosine, imipramine, and placebo in 65 outpatients with major depression over 4 weeks. Tyrosine increased MHPG excretion but showed no antidepressant activity. Imipramine decreased MHPG excretion and caused greater dry mouth.
Effects of selective and combined serotonin and dopamine depletion on the loudness dependence of the auditory evoked potential (LDAEP) in humans.
The study examined the effects of selective serotonin, dopamine, and combined serotonin and dopamine depletion on the loudness dependence of the auditory evoked potential (LDAEP) in 14 healthy subjects. Despite significant depletion of monoamine precursors, no effects on the LDAEP were observed, suggesting insensitivity to acute changes in serotonin and dopamine neurotransmission.
Tyrosine improves working memory in a multitasking environment.
RCT examining the effects of tyrosine ingestion on performance during multitasking and simple task batteries. Tyrosine significantly enhanced accuracy and decreased list retrieval frequency on the working memory task during multitasking, but did not affect other tasks. Heart rate and blood pressure increased during tasks.
Randomised controlled trial of tyrosine supplementation on neuropsychological performance in phenylketonuria.
RCT testing the efficacy of tyrosine supplementation on neuropsychological performance in 21 individuals with phenylketonuria. Tyrosine increased plasma concentrations but did not alter neuropsychological test performance compared to placebo.
L-tyrosine ameliorates some effects of lower body negative pressure stress.
RCT testing the effects of tyrosine (100 mg/kg) on humans exposed to cardiovascular stress via Lower Body Negative Pressure. Tyrosine increased pulse pressure and auditory event-related potential amplitude, suggesting enhanced cognitive activation and stress amelioration.
Utilization of tyrosine-containing dipeptides and N-acetyl-tyrosine in hepatic failure.
The study evaluated the elimination and hydrolysis of tyrosine sources (Ala-Tyr, Gly-Tyr, and Nac-Tyr) in six patients with hepatic failure and seven healthy subjects. In hepatic failure, elimination and hydrolysis of Ala-Tyr and Gly-Tyr were comparable to controls, but Cltot of Nac-Tyr was reduced. Ala-Tyr and Gly-Tyr may serve as tyrosine sources in parenteral nutrition, while Nac-Tyr was not effective in increasing plasma tyrosine levels.
Amino acid solutions for premature neonates during the first week of life: the role of N-acetyl-L-cysteine and N-acetyl-L-tyrosine.
RCT comparing three amino acid solutions for low-birth-weight neonates on total parenteral nutrition. Aminovenös-N-päd 10% contains acetylated tyrosine and cysteine, leading to higher plasma levels of these amino acids compared to non-acetylated forms. The study suggests acetylation improves amino acid stability and solubility, facilitating better nutrition.
Tyrosine reverses a cold-induced working memory deficit in humans.
RCT with 8 male volunteers testing the effect of tyrosine on cold-induced working memory deficits. Tyrosine improved matching accuracy in a delayed matching-to-sample task under cold stress, aligning performance with non-cold conditions.
Treatment of narcolepsy with L-tyrosine: double-blind placebo-controlled trial.
A randomized, double-blind, placebo-controlled study of L-tyrosine in 10 subjects with narcolepsy and cataplexy. Tyrosine treatment showed significant differences in three mood and arousal scales (less tired, less drowsy, more alert) but no significant differences in other measures of narcoleptic symptoms or overall clinical response.
[L-tyrosine cures, immediate and long term, dopamine-dependent depressions. Clinical and polygraphic studies].
Twelve patients with dopamine-dependent depression received oral L-tyrosine (3,200 mg/day). Immediate improvements in mood and sleep parameters were observed, with successful treatment reported in over 50 patients for periods up to 2 years. The treatment was ineffective in other types of depression.
Modulation of the actions of tyrosine by alpha 2-adrenoceptor blockade.
The study investigated the effects of L-tyrosine on hormone secretion in eight normal subjects. Tyrosine increased plasma concentrations dose-dependently and stimulated prolactin and TSH secretion, but not ACTH, cortisol, growth hormone, or gonadotrophins. The alpha 2-adrenoceptor antagonist idazoxan was used to test the hypothesis that tyrosine's lack of effect on ACTH was due to negative feedback mechanisms. With idazoxan pretreatment, tyrosine stimulated ACTH and noradrenaline secretion.
An open trial of L-tyrosine in the treatment of attention deficit disorder, residual type.
An open 8-week trial of L-tyrosine in 12 adults with attention deficit disorder, residual type. Eight participants showed marked to moderate clinical response in 2 weeks, but developed tolerance by 6 weeks, suggesting L-tyrosine is not useful for this condition.
Tyrosine for the treatment of depression.
The paper reviews the theoretical background and clinical experience with using neurotransmitter precursors, focusing on L-tyrosine, for treating depression. It discusses the potential of tyrosine to increase brain levels of norepinephrine and serotonin, thereby enhancing presynaptic activity and acting as an antidepressant.