Research review
Does L-tyrosine help with weight loss? What the research does and doesn't show
No trial has tested L-tyrosine supplementation for weight loss, body fat or body weight as an outcome. Two exercise trials found mixed results on performance in the heat, and a 2020 case report described acute liver failure in a man taking a multi-ingredient 'fat burner' blend that included N-acetyl-L-tyrosine.
No trial has tested L-tyrosine supplementation for weight loss, body fat or body weight as an outcome. Tyrosine is the raw material the body uses to make norepinephrine, a hormone involved in metabolic rate and fat breakdown — a real mechanism, but one no trial has connected to an actual change in weight from taking a tyrosine supplement.
What the evidence doesn't support
It doesn't support L-tyrosine as a weight-loss aid. No trial has given people a tyrosine supplement and measured body weight, body fat percentage, or waist circumference as an outcome. The closest research measures exercise performance and energy expenditure under specific conditions, not weight change over time, and even that narrower research found mixed and mostly null results.
What the trials found
A 2014 randomized crossover trial gave 7 trained cyclists 150 mg/kg of tyrosine an hour before a self-paced cycling time trial in 30°C heat. Plasma tyrosine availability rose 2.5-fold, but power output and time-trial performance didn't differ from placebo. A related 2013 trial took the opposite approach: it gave 8 moderately trained men an amino acid drink stripped of tyrosine and phenylalanine before cycling to exhaustion in the heat, and found that depleting the body's tyrosine pool shortened exercise time compared with a balanced drink — evidence that the precursor pool matters for exercise capacity under heat stress, though the companion trial found adding extra tyrosine on top of a normal diet didn't extend performance further. Neither trial measured body weight, fat mass, or energy expenditure as an outcome — they measured how long or how hard someone could exercise in a single session, a different question from whether a tyrosine supplement changes body composition over time.
Separately, a 2020 case report described a 36-year-old man who developed acute liver failure and ultimately needed a liver transplant after taking a thermogenic "fat burner" supplement containing N-acetyl-L-tyrosine along with caffeine, white willow bark and another stimulant compound. The report couldn't identify which ingredient caused the injury, and no other published report links tyrosine itself to liver damage — but it's a real documented case involving a tyrosine-containing weight-loss product, worth knowing given how often tyrosine shows up in that category of supplement.
Questions people ask
Can L-tyrosine help with weight loss?
No trial has tested it for that outcome. The mechanism some marketing points to — tyrosine feeding norepinephrine production — is real biochemistry, not a tested weight-loss effect.
How much L-tyrosine should I take for weight loss?
There's no dose to recommend, because no trial has tested a dose against weight loss as an outcome. L-tyrosine dosage covers what doses have actually been tested, all for other outcomes.
Can L-tyrosine cause weight gain?
No trial reviewed on this site has reported weight gain as a side effect of L-tyrosine taken alone.
Is L-tyrosine safe in a "fat burner" or thermogenic blend?
A 2020 case report described acute liver failure in a man taking a multi-ingredient thermogenic supplement that included N-acetyl-L-tyrosine, caffeine, white willow bark and another stimulant — the report couldn't pin the cause on any one ingredient. That's a reason to read the full ingredient list on any "fat burner" product and be cautious about stacking stimulants, not a finding specifically against tyrosine.
When to talk to a doctor
A doctor, not a supplement, is the right first step for a weight-management plan. L-tyrosine is not a weight-loss treatment. If you take medication for weight, blood pressure, or any other condition, or you're combining multiple supplements in a "fat burner" product, talk to a doctor first; see L-tyrosine and medications: what to check.
Related reading: L-tyrosine benefits: what the research does and doesn't show, L-tyrosine side effects, and L-tyrosine dosage.
Sources
- Failure of oral tyrosine supplementation to improve exercise performance in the heat A 2014 randomized crossover trial found 150 mg/kg of oral tyrosine, taken an hour before exercise, did not improve self-paced cycling time-trial performance in the heat compared with placebo in 7 trained cyclists, despite a 2.5-fold rise in plasma tyrosine availability.
- Acute oral administration of a tyrosine and phenylalanine-free amino acid mixture reduces exercise capacity in the heat A 2013 trial found that acutely depleting the body's tyrosine (and phenylalanine) pool shortened cycling time to exhaustion in the heat compared with a balanced amino acid drink — evidence the precursor pool matters for exercise capacity in the heat, though a separate 2014 trial found adding extra tyrosine on top of a normal diet didn't extend performance further.
- Acute Liver Failure Caused by Use of Fat Burner: A Case Report A 2020 case report described a man who developed acute liver failure and needed a liver transplant after taking a multi-ingredient thermogenic supplement containing N-acetyl-L-tyrosine along with caffeine, white willow bark and another stimulant compound; the report could not attribute the injury to any single ingredient, and no other report links tyrosine itself to liver damage.
*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.