Guide
L-tyrosine side effects
The controlled trials reviewed here describe L-tyrosine as generally well tolerated, even at single doses several times larger than a typical commercial serving; a brief, early dip in blood pressure was reported in one study, and none reported drowsiness or a mood effect.
The controlled trials reviewed here describe L-tyrosine as generally well tolerated, including at single doses several times larger than a typical commercial serving. The most notable finding across them is a brief, early dip in blood pressure in one trial; none reported drowsiness or a negative mood effect.
What the trials actually reported
A 1995 trial testing 150 mg/kg of tyrosine — about 10.5 g for a 70 kg (154 lb) adult, given in a night of sleep loss — described it as a relatively benign treatment at that dose (PMID 7794222). A 1994 trial using a 100 mg/kg dose found diastolic blood pressure dipped 15 minutes after ingestion, was back in line with placebo by the 1-hour mark, and found no effect on mood, systolic blood pressure or heart rate (PMID 8293316). A 1999 field trial giving 21 military cadets 2 g of tyrosine daily for 5 days found systolic blood pressure had decreased by day 6 compared with a carbohydrate drink, again with no effect on mood (PMID 10230711). And a 1990 trial in 65 people with depression, using 100 mg/kg/day for 4 weeks, found no tyrosine-specific side effect reached statistical significance against placebo over that period (PMID 2142699).
Put together, blood pressure is the one measurement that moved in more than one trial — down, modestly, not up — and mood, heart rate and general tolerability came back unremarkable across every trial that measured them. None of this is a comprehensive safety survey; it's what these specific trials, in these specific groups of people, happened to measure and report.
Blood pressure
If you have low blood pressure, or take a blood pressure medication, the pattern above — a modest decrease reported in two separate trials — is worth mentioning to a doctor before adding a tyrosine supplement, since that reported direction is one a doctor overseeing blood pressure medication would want to know about before it's compounded with anything else. See who should not take L-tyrosine? for more on who should ask first.
Questions people ask
Does L-tyrosine have side effects?
In the trials reviewed here, the main reported effect beyond the intended cognitive-performance measures was a modest blood-pressure decrease in two separate studies. No trial reported drowsiness, mood changes, or a tyrosine-specific side effect reaching statistical significance against placebo.
Can L-tyrosine make you sleepy?
None of the trials reviewed here reported drowsiness as an effect of tyrosine. One trial found it helped maintain alertness during a night of sleep loss rather than causing sleepiness (PMID 7794222) — the opposite of what a sedating effect would look like.
Can L-tyrosine cause dizziness?
No trial we reviewed reported dizziness specifically. A brief, early dip in blood pressure was reported in one trial (PMID 8293316); blood pressure changes can sometimes cause lightheadedness in sensitive individuals, though that specific symptom wasn't reported in this research.
Does L-tyrosine have long-term side effects?
The longest trial reviewed here ran 4 weeks (PMID 2142699); none of the research we found followed people for months or years of continuous use, so there's no long-term safety data to report either way.
Related reading: who should not take L-tyrosine?, L-tyrosine and medications: what to check, and how much L-tyrosine should you take a day?
Sources
- The effects of tyrosine on cognitive performance during extended wakefulness A 1995 trial found that 150 mg/kg of tyrosine, given partway through a night of sleep loss, reduced the usual decline in psychomotor performance and vigilance lapses for about 3 hours compared with placebo, and was well tolerated at that dose.
- Effect of tyrosine on cognitive function and blood pressure under stress A 1994 crossover trial in 16 healthy adults found a single 100 mg/kg dose of tyrosine improved performance on two stress-sensitive cognitive tasks under noise stress, with a brief, early dip in diastolic blood pressure and no effect on mood, systolic blood pressure or heart rate.
- Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course A 1999 field trial gave 21 military cadets either 2 g/day of tyrosine or a calorie-matched carbohydrate drink for 5 days during a combat training course; the tyrosine group performed better on memory and tracking tasks and had lower systolic blood pressure, with no difference in mood.
- Tyrosine for depression: a double-blind trial A 1990 double-blind trial gave 65 outpatients with major depression 100 mg/kg/day of L-tyrosine or placebo for 4 weeks; tyrosine raised a norepinephrine breakdown product in urine but showed no evidence of antidepressant activity over placebo.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.