A dietary amino acid the body already makes from protein. In rested, unstressed people it changes little. Under cold, low oxygen, loud noise or lost sleep it preserves memory and alertness for a few hours; older adults hold body heat better in the cold. Short courses are well tolerated; long-term use is unresolved. (Full Review)

Protocol

Standard practitioner dose

500–2,000 mg

Free-form L-Tyrosine on an empty stomach, 30–60 minutes before the cognitive or physical demand rather than on a fixed daily schedule

Best time of day

Morning to early afternoon

Effects on focus emerge 30–45 minutes after ingestion; dosing after mid-afternoon risks delayed sleep onset

Age-related adjustment

500–1,000 mg over 60

Adults over 60 reach substantially higher plasma tyrosine on the same per-kilogram dose, so protocols cap rather than scale by body mass

Time to effect

30–45 minutes

Acute. Plasma tyrosine rises and the behavioural window closes by about three hours; no loading phase

Half-life

90–120 minutes to peak

Plasma tyrosine remains elevated for roughly four hours; the effective behavioural window in trials was about three hours

Duration of use

Short-term

Safety data extend to about three months at up to 150 mg/kg daily; nothing supports lifelong daily use

Benefits

High: Preserved cognitive performance during acute environmental and sleep stress

Medium: Better core temperature maintenance during cold exposure in older adults; lower blood pressure under acute psychological stress

Low: Enhanced inhibitory control without an imposed stressor; endurance capacity when mental fatigue precedes exercise; mood improvement in depression; symptom reduction in attention-deficit/hyperactivity disorder

Speculative: Support of thyroid hormone production; restoration of tyrosine status on phenylalanine-restricted diets

Contraindications

Hyperthyroidism, thyrotoxicosis or untreated Graves' disease

Personal history of malignant melanoma at any stage

Taking a monoamine oxidase inhibitor, or within 14 days of stopping one

Parkinson's disease taking levodopa, unless doses are strictly separated

Bipolar disorder or a psychotic disorder

Hereditary tyrosinemia types I, II or III, or alkaptonuria

Pregnancy at any supplemental dose; breastfeeding above dietary intake

Child-Pugh Class B or C liver impairment

Key Interactions

Thyroid hormone replacement (levothyroxine, liothyronine)

Stimulants, over-the-counter decongestants and caffeine (pseudoephedrine, phenylephrine, methylphenidate, amphetamine salts)

Supplements with additive catecholamine or thyroid effects (L-Phenylalanine, N-Acetyl-L-Tyrosine, Mucuna pruriens, iodine, kelp, Withania somnifera, synephrine, yohimbine)

Other interventions (cold exposure protocols, fasted high-intensity training, stimulant preworkout)

Risk & Side Effects

Medium: Increased anger and irritability under severe stress; impaired working memory in older adults at higher doses; higher circulating tyrosine tracks with shorter lifespan and metabolic disease

Low: Gastrointestinal upset, nausea, headache and fatigue; reduced levodopa effect in Parkinson's disease

Speculative: Additive thyroid stimulation in thyroid disease; fuelling of melanoma; blood, liver and kidney changes on extreme chronic intake; delayed sleep onset after late dosing

Monitoring

Marker	Target	Why
TSH	0.5–2.0 mIU/L	Detects thyroid overstimulation
Free T4	1.0–1.5 ng/dL	Confirms hormone output is stable
Free T3	3.0–4.0 pg/mL	Tracks the active hormone most likely to shift
TPO antibodies	Negative or below assay cut-off	Identifies autoimmune thyroid disease before starting
Plasma tyrosine (fasting)	45–90 µmol/L	Establishes whether a deficit exists and whether dosing has pushed levels high
Seated blood pressure	Below 120/80 mmHg	Trials recorded shifts under stress, and combination with stimulants can raise it
Fasting glucose	75–86 mg/dL	Anchors the metabolic risk signal tied to elevated tyrosine
HbA1c	Below 5.4%	Tracks the diabetes endpoint linked to circulating tyrosine
eGFR	Above 90 mL/min/1.73 m²	Screens for reduced clearance before higher-dose use
ALT	10–26 U/L (men), 8–22 U/L (women)	Screens liver function, the site of tyrosine breakdown

Cadence: Thyroid function and blood pressure rechecked at six to eight weeks, then every six to twelve months if use continues; fasting glucose, glycated haemoglobin and plasma tyrosine repeated annually for anyone dosing more than occasionally.

Qualitative Assessment

Subjective focus and task persistence during the 30-minute to 3-hour window after dosing, rated on a simple 1–10 scale
Whether the benefit appears only on stressed, cold or sleep-deprived days
Irritability or anger, the one mood change a controlled trial has isolated
Sleep onset latency on dosing days versus non-dosing days
Nausea, heartburn or headache within an hour of the dose
Whether the perceived effect fades over consecutive weeks of daily use, which would indicate tolerance

L-Tyrosine for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment