If you want to know what L-tyrosine is, why people supplement with it, and whether or not it can benefit you, then you want to read this article.

Key Takeaways

  1. L-tyrosine is an amino acid that’s often taken to promote fat loss and exercise performance since it can turn into dopamine and adrenaline.
  2. It works quite well for preventing the effects of major acute stress but not so much for chronic stress or fat burning.
  3. L-tyrosine helps prevent the normal drop in dopamine that occurs during cold stress and when you switch between cognitively demanding tasks.

It’s not the most popular fat burner—that would be caffeine.

Nor is it the most effective fat burner—that’s probably ephedrine.

Frankly, it doesn’t even work for fat burning.

So why is it in every fat burner out there? And why is it in Phoenix?

Enter, L-tyrosine, the misunderstood amino acid.

Grandfathered into almost every fat burning supplement it, much like it’s namesake the Tyrannosaurus Rex (shut up, I can dream), is an ancient inclusion into most pre-workouts and fat burners that nobody really questions anymore.

Look around a bit and you’ll see many people saying “It’s used to create dopamine and adrenaline” which, is true I guess, but it’s met with a resounding “Oh, okay” and that claim is just assumed to be sufficient.

Of course, many products also opt for NALT (N-acetyl L-tyrosine) for… some reason?

If you want to sell creatine nitrate then go ahead, do a questionable build on a proven molecule. Want to sell alanyl-glutamine? Build on a somewhat proven molecule.

But why build upon a molecule and get “the better form” of something that might not even be doing what you want it to do?

It’s not a fat burner, but it’s still cool. Let’s find out why.

What Is L-Tyrosine?

L-tyrosine is a dietary amino acid. It’s one of the aromatic amino acids (having a ring in it’s structure) but, more practically, it’s a precursor to some popular neurotransmitters.

L-tyrosine turns into a molecule called L-DOPA, which is also a dietary supplement. After that, L-DOPA can turn into the neurotransmitters that we collectively call the “catecholamines” (dopamine, epinephrine, and norepinephrine); the latter two are sometimes referred to as “adrenaline” and “noradrenaline” respectively.

The difference between L-tyrosine and L-DOPA, however, is that L-tyrosine occurs before the “rate-limiting” step; the enzyme called tyrosine hydroxylase. L-DOPA comes after this step.

Rate-limiting steps are also safety checks; things that come before it have less risk yet less potency while those that flood the body after them are higher risk but with higher potency (as a general rule of thumb).

It’s kind of like a bouncer keeping an eye out for the maximum amount of people allowed in the club before the place gets shut down by the fire department for safety reasons.

If you go by the rate-limiting bouncer then the place is safe since it is well controlled but the real party only starts, for better or for worse, when you and a few dozen friends slip through the back door.

L-tyrosine and L-DOPA are both supplements that are used to increase catecholamine levels in the body. L-tyrosine is seen as the weaker, but safer, option while L-DOPA the more effective but riskier option.

Why Do People Supplement with L-Tyrosine?

l tyrosine

L-tyrosine is supplemented almost exclusively for it’s link to the catecholamines.

This means that, when it’s in a supplement, people are taking it under the impression that it can either increase catecholamine synthesis or at least prevent catecholamines from being depleted.

That’s really all L-tyrosine is known to do appreciably after all.

Of course this is then linked to improvements in cognitive function, improved physical performance, improved metabolic rate and resultant fat loss, and possible usage as a stimulant to stave off tiredness.

Unfortunately L-tyrosine is inferior to L-DOPA (and many other supplements) for most, but not all, of these purposes.

What Are the Benefits of L-Tyrosine?

The benefits of L-tyrosine, for the most part, come from preventing abnormal decreases in catecholamines.

I know L-tyrosine could technically turn into the catecholamines but, let’s be real, it’s far too regulated to do that. Don’t expect this to be a stimulant.

L-Tyrosine and Acute Stress

L-Tyrosine has a series of unique studies on it investigating cold stress.

Cold stress is a term used to refer to physical stress caused to the body simply by cold exposure, rather than any actual exercise; it underlies the benefits of cold exposure but, at the same time, could be debilitating if not careful.

They’re unique in the sense that they’re on highly trained military personnel, and that they use very high doses.

When looking at studies that put some sort of major stress on the subject, 10 grams a day (in five divided doses of 2 grams) or a dose of 100 mg/kg are able to mitigate some of the effects of stress during environmental and high intensity training stressors.

This includes stabilization of blood pressure, mood, and preventing a stress-induced decline in cognition that also happens during sleep deprivation (150 mg/kg can mitigate the cognitive side effects of being sleep deprived) and working memory.

It should be noted that the above benefits are either for high intensity training or, for “environmental” stressors like cold stress. The evidence is mixed on whether or not L-tyrosine is useful for exercising in the heat with some positive and some null results; although it seems amino acids actually worsen performance if L-tyrosine (and phenylalanine) aren’t in the drink.

Ultimately, high dose L-tyrosine supplementation can mitigate many side effects of high intensity acute stressors like cold exposure or heavy and prolonged training (think boot camp style stuff).

This is due to the stress response in humans.

For short term stressors the catecholamines mediate how our bodies respond to what’s happening. Just having catecholamines is good enough to prevent many side effects of stress and, hopefully, you can escape the threat before they get depleted.

If the threat doesn’t go away then the body either attempts to shift the stress response from catecholamines (that mediate short term stuff) over to cortisol (which mediates long-term stuff). If the body fails to do that and runs out of catecholamines then, well, you fall on your face and get highly stressed out.

L-tyrosine simply provides extra material floating around to delay the inevitable fall, for a while at least, but this requires a decent amount of L-tyrosine in your body to pull off hence why the doses are so high.

L-tyrosine simply delays the inevitable succumbing to high intensity stressors and allows you to perform better during that time.

L-Tyrosine and Cognitive Flexibility

While L-tyrosine has been shown (in the previous section) to improve cognition in states of acute stress, it can potentially do a bit more in low stress situations.

A series of studies using 2 grams of L-tyrosine before cognitive testing in otherwise healthy subjects has found that L-tyrosine can help during task-switching, or going from one task to another (i.e. cognitive flexibility). Specifically, supplementation helps you “stop” a task so you can start another.

You can view this through the framework of the “fight or flight” response. If our ancestors on the plains of Africa heard a growl in the bushes they needed the machinery in their brains to seek, scan, and analyze every area around them before seeing the inside of a lion’s intestinal tract.

This is thought to be related to supporting dopamine levels in certain brain regions since, for people who are genetically prone to have lower levels in that part of the brain, L-tyrosine at this dose seems to be more effective.

This greater effect is also seen in those who are more sensitive to cognitive stressors (it may very well be two ways of looking at the same issue—that people who are easily stressed are more easily stressed out since dopamine depletes faster).

For tasks that require you to switch cognition from one target to the next, L-tyrosine supplementation at two grams seems to be useful in improving performance.

What Does L-Tyrosine Fail to Do?

l tyrosine supplementation

L-tyrosine is in a weird spot where, as soon as it was discovered what it did, a lot of research went on to investigate the “better” molecules such as L-DOPA and modafinil leaving L-tyrosine in a sort of lonesome state.

It doesn’t actually get much dedicated research these days and a good chunk of what was cited was from the early 2000s or 90s, before research moved on ahead of it.

As such, research that puts L-tyrosine down in the “does not do this” category is also limited. Not absent, however, and perhaps the most popular claim of L-tyrosine falls under this category.

L-Tyrosine and Fat-Burning

L-tyrosine is claimed to be a fat burner due to its connection to the catecholamines.

Dopamine has many roles in the brain but the two adrenaline molecules (epinephrine and norepinephrine) have both central (brain) and peripheral (everything below the neck) roles. In fact it is their receptors, the beta-adrenergic receptors, that underlie the fat burning effects of ephedrine.

Any supplement that can provide a sustained increase in adrenaline-like activity, through these receptors, can then increase fat burning.

One catch, however, is that epinephrine (the adrenaline molecule that acts in the periphery) has a very short half-life. 11 minutes being the highest estimate (from injections) but usually said to be 2 to 3 minutes. It’s too short for this exact molecule to do the fat burning.

It’s why in fat burners you have seen a shift from epinephrine to “things that can mimic epinephrine but stay in the blood longer” like ephedrine, synephrine, and higenamine. L-tyrosine, by itself, is not something that activates epinephrine receptors (rather, L-tyrosine is literally a part of the receptor).

There isn’t any direct evidence to outright show that L-tyrosine doesn’t burn fat but let’s go down the checklist:

  1. It helps the catecholamines stick around longer, it doesn’t increase their production outright.
  2. Even if it did, increasing production of epinephrine isn’t the best way to burn fat since it doesn’t stick around in the body for long after it’s made.
  3. L-tyrosine doesn’t have the ability to mimic epinephrine at the receptor, which is how you would get the fat burning effects of epinephrine without actually increasing it.

The connection of L-tyrosine to fat burning is nothing more than semantic, being the building block that adrenaline molecules are made from, and is highly unlikely to have a direct role in causing fat loss.

What’s the Clinically Effective Dosage of L-Tyrosine?

The clinically effective dose of L-tyrosine is a tricky one because, unlike pretty much every other supplement in existence, the most common supplemented dose is far below what you’d expect the dosage to be based on the previously mentioned studies on acute stress.

To reiterate, the dosage of L-tyrosine that’s used with benefit to stave of the effects of acute stress is 100 to 150 mg/kg bodyweight or:

7 to 10 grams for a 150 pound person

9 to 14 grams for a 200 pound person

11 to 17 grams for a 250 pound person

These are doses that are as big as a third to half a scoop of protein powder, not doses that can be fit into dinky little capsules.

Ultimately, however, if you want the acute-stress mitigating effect of L-tyrosine you are going to need quite a high dose. A dose far above what you will find in any fat burning supplement.

Despite the above doses most fat burners and pre-workouts still contain L-tyrosine at about 100 to 500 mg; even Phoenix has it at 150 mg, so what gives? Is this too low a dose to have the acute-stress mitigating effect?


The lowest dose used in human studies is two grams and, if we were to look at the lowest dose used in rat studies for acute stresses (200 mg/kg) the estimated human equivalent is 32 mg/kg or… about two grams again.

So if the doses are too low to even confer a benefit why are they even included in Phoenix? Well, it’s a form of a safety buffer for numerous reasons.

Firstly, providing amino acids to rats without L-tyrosine actually causes tyrosine depletion since BCAAs themselves might reduce L-tyrosine availability if L-tyrosine is not co-ingested. This seems to be relevant to dopamine (even in healthy people) but, oddly enough, not noradrenaline.

On one hand this could be useful to people who are addicted to stimulants, since L-tyrosine depletion impairs the effects of stimulants, but for our purposes that would be shooting ourselves in the feet. We want stimulant effects in fat burners.

So, best course of action? Put the stuff that actually works in a fat burner and, since BCAAs are a popular stand-alone supplement, add in a small amount of L-tyrosine that reflects dietary levels somewhat to try and mitigate this unforeseen side effect when multiple supplements are taken.

So if you have a BCAA habit and are feeling a lack of focus as of late, well, now you know why. Get some L-tyrosine.

Low doses of L-tyrosine, in fat burning supplements, are unlikely to promote any beneficial effects by themselves but tend to be included in a harm-preventative approach so dopamine signaling is not unnecessarily impaired.

In other words, if you take so much BCAAs that it makes you fatigued and reduces focus then a fat burner won’t work as well unless the L-tyrosine issue is addressed.

Better safe than sorry, and on that note…

Is L-Tyrosine Safe?

l tyrosine safe



At this moment in time, studies using L-tyrosine supplementation fail to find any major side effects aside from potential gastrointestinal distress when taking a very large dose at once (which can happen with anything).

For the purpose of mitigating acute cold stress and stress from heavy and prolonged training, taking a dose of 15+ grams of L-tyrosine may very well upset the stomach. It’s best to take it in divided doses, with or without food, throughout the day before exercise.

Beyond that there don’t seem to be any side effects pertaining to forcing excessive catecholamine signaling, likely due to how L-tyrosine is before the rate limit rather than after.

L-DOPA, on the other hand, could be a problem (just look into the side effects associated with the pharmaceutical “Levodopa”; it’s literally L-DOPA and has some concerning sides if not taken carefully).

Because L-tyrosine sustains, rather than forces an increase, of catecholamines it’s also thought to be a very low-risk supplement when combining with other stimulants (again, unlike L-DOPA).

High doses of L-tyrosine supplementation are safe beyond the potential intestinal distress from taking too much at once. The small precautionary dose in fat burners should also be completely without harm.

The Bottom Line on L-Tyrosine

L-tyrosine is essentially a preventative amino acid.

It does not cause changes in the body, it prevents abnormalities from occurring, like reduced cognition and focus from prolonged exercise. If you don’t want those abnormalities to happen then it’s best to have a bit of L-tyrosine.

For people who exercise in cold environments and feel the cold nagging at their bones and reducing exercise performance, consider L-tyrosine. It doesn’t prevent the benefits of cold exposure but, rather, allows you to get those benefits for a longer period.

It’s also a valid consideration for stressful cognitive tasks that require you to switch attention from one target, to the next, back to the first target, to another, and so on and so forth for hours on end.

Soldiers and call center workers alike can benefit from L-tyrosine.

Just conveniently ignore all claims pertaining to fat burning. But, if you see it in a fat burner, know that it might have a few other benefits (Ya’ know, like, say, Phoenix.)

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What’s your take on L-tyrosine? Have anything else to share? Let me know in the comments below!