Tyrosine

An RCT of 28 healthy men found that a single 2 g tyrosine dose reduced reaction times, lowered decision thresholds, and reduced autonomic arousal during cognitive tasks versus placebo.

An RCT of 42 office workers found that a five-amino-acid blend including tyrosine (SAGAT) for 4 weeks significantly improved motivation and cognitive function after mental work versus placebo.

A systematic review found mixed evidence that dietary supplements including multivitamins improve cognitive performance in younger adults.

An RCT of 26 adults found tyrosine decreased consciously perceived conflicts in a Simon task but increased subliminally triggered conflicts when concurrent control demands were present.

An RCT of 17 older adults found dose-dependent increases in plasma tyrosine with oral tyrosine (100–200 mg/kg), associated with dose-dependent declines in working memory performance.

An RCT of 8 soccer players found that 150 mg/kg tyrosine improved vigilance during intermittent exercise in heat but did not improve total distance covered.

A controlled study of 19 volunteers found that 300 mg/kg tyrosine mitigated cold-induced working memory decrements on Match-to-Sample and choice RT tasks versus placebo.

A controlled study of 15 subjects found that 300 mg/kg tyrosine preserved working memory and marksmanship performance during cold water immersion versus placebo.

A crossover study of sleep-deprived men found that 150 mg/kg tyrosine improved running memory, logical reasoning, tracking, and visual vigilance, though less effectively than D-amphetamine.

An RCT of 21 military cadets found that 2 g/day tyrosine for 5 days during combat training improved memory and tracking performance and reduced systolic blood pressure versus carbohydrate placebo.

An RCT of 20 adults found that 150 mg/kg tyrosine significantly enhanced working memory accuracy during a multitasking battery but did not improve performance on simpler tasks.

An RCT of 20 participants found that 100 mg/kg L-tyrosine increased pulse pressure and P300 amplitude during lower body negative pressure stress versus placebo.

An RCT during 24 h sleep deprivation found that 150 mg/kg tyrosine significantly ameliorated performance decline on a psychomotor task and reduced vigilance lapses for about 3 hours.

An RCT of 16 young adults found that 100 mg/kg tyrosine improved performance on two stress-sensitive cognitive tasks and transiently lowered diastolic blood pressure under 90 dB noise stress.

A controlled study found that 150 mg/kg tyrosine reversed cold-induced working memory deficits on a delayed matching-to-sample task at 4°C versus placebo.

A crossover study found that 100 mg/kg tyrosine significantly reduced symptoms, adverse moods, and performance impairments during 4.5 hours of cold and hypoxia exposure in stress-sensitive subjects.

A crossover RCT of 12 untrained men found that a multi-ingredient pre-workout with tyrosine significantly improved peak and mean power in the Wingate anaerobic test versus placebo.

In 15 resistance-trained men, anhydrous caffeine alone produced greater bench press repetition volume than a multi-ingredient pre-workout supplement containing caffeine, with no differences in perceived exertion or arousal.

An RCT of 8 men found that 150–400 mg/kg tyrosine did not improve cycling time trial performance in a warm environment despite increased plasma tyrosine ratios.

An RCT of 7 endurance-trained men found that 150 mg/kg tyrosine did not improve self-paced cycling time trial performance in 30°C heat versus placebo.

An RCT of 8 men found that 150 mg/kg tyrosine significantly extended cycling endurance in heat (80.3 vs 69.2 min) and reduced perceived exertion versus placebo.

An RCT of 20 men found that 150 mg/kg tyrosine had no significant effect on treadmill endurance, handgrip strength, or stair-stepping anaerobic power versus placebo.

An RCT of 9 cyclists found that 25 mg/kg L-tyrosine did not improve time trial performance after 90 min of steady-state cycling; carbohydrate improved performance but tyrosine did not.

A controlled study of 10 men found that 20 g tyrosine altered neuroendocrine responses during exercise but did not improve endurance performance; BCAA improved post-exercise drive on psychometric tests.

An RCT of 18 older adults found that 150 mg/kg oral L-tyrosine augmented cutaneous vasoconstriction during whole-body cooling and improved core temperature maintenance versus placebo.

An RCT of 11 older adults found that 150 mg/kg L-tyrosine augmented sympathetically mediated vasoconstriction during whole-body cooling versus placebo.

A double-blind study found that oral tyrosine ingestion caused a short-lived increase in plasma norepinephrine, dopamine, and epinephrine within 45 minutes in fasted men.

A crossover study found that 7.5 g/day oral tyrosine significantly decreased plasma norepinephrine concentrations, suggesting increased central catecholaminergic activity reducing peripheral sympathetic tone.

An RCT of 10 narcolepsy patients found that 9 g/day L-tyrosine for 4 weeks produced only mild stimulant effects on mood ratings with no significant improvement in cataplexy or sleep latency.

An RCT of 36 Parkinson's patients found that 1000 mg/day L-tyrosine for 7 days was safe but did not improve orthostatic hypotension, blood pressure, or autonomic exercise responses.

A double-blind RCT in cocaine-dependent inpatients found that L-tryptophan and L-tyrosine did not significantly reduce most cocaine craving and withdrawal symptoms versus placebo.

A study of 10 dementia patients found that tyrosine (4 g/day) plus 5-HTP (800 mg/day) improved clinical and psychologic outcomes in 2 of 10 patients with multi-infarct or mixed dementia.

An RCT of 65 outpatients with major depression found that 100 mg/kg/day L-tyrosine for 4 weeks did not show antidepressant activity versus imipramine or placebo.

An RCT of 13 patients with mild essential hypertension found that 2.5 g tyrosine three times daily for 2 weeks did not affect blood pressure or plasma norepinephrine versus placebo.

An RCT found that tyrosine supplementation selectively improved inhibitory control on a stop-signal task without affecting response execution speed versus placebo.

An RCT of 78 military personnel found that 300 mg/kg tyrosine during SERE stress training increased anger ratings but did not alter most mood, cortisol, or heart rate responses.

An RCT of 57 obese adults found that an 8-week tyrosine-containing thermogenic supplement increased 4-hour thermogenesis by ~90 kJ and reduced body fat mass by 0.9 kg more than placebo.

An RCT of schizophrenia inpatients found that 10 g/day L-tyrosine adjunct to molindone for 3 weeks did not improve BPRS, SANS, or CGI scores versus placebo.

An RCT of 19 adults found that topical ascorbic acid applied daily for 3 months significantly improved photodamaged skin topography, fine wrinkling, and tactile roughness versus vehicle.