L-Tyrosine vs N-Acetyl-L-Tyrosine: Which to Choose and for Whom

On the shelves of sports nutrition, L-tyrosine and N-acetyl-L-tyrosine (NALT) stand side by side, and NALT is often more expensive and presented as a “progressive” form. The editorial team explains in which situations tyrosine makes sense at all, why classic L-tyrosine is more logical for most people, and for whom it is better to give up both forms.

When tyrosine may be useful and when not

Tyrosine is not a stimulant. It does not raise the dopamine level at rest the way caffeine or other psychoactive substances do. Its potential value lies in supporting the synthesis of catecholamines when the body spends them especially intensively.

In studies, beneficial effects were observed in situations of acute stress: cold and hypoxia (Banderet and Lieberman, 1989), intensive military training (Deijen et al., 1999), sleep deprivation, and also in tasks involving multitasking and updating of working memory (Colzato et al., 2013). The review by Jongkees and colleagues (2015) summed up precisely this pattern.

In contrast, in rested people performing ordinary tasks, the effect of tyrosine is usually not detected. Therefore taking it “every day for productivity” has little basis, and expectations of a “noticeable surge” most often end in disappointment.

For physical exertion the data are contradictory. Tumilty and colleagues (2011) reported a longer time to exhaustion during cycling exercise in the heat, but a number of other works found no improvement in endurance or strength under normal conditions.

Why L-tyrosine is more logical for most people

The first argument is the evidence base. Practically all studies of effects under stress were carried out precisely with L-tyrosine. By choosing NALT, a person is in effect buying a product that has not been tested under such conditions.

The second argument is conversion. NALT must first lose its acetyl group, and the data from intravenous administration (Magnusson et al., 1989) showed that a significant part of the substance is excreted in the urine unchanged. There is no direct evidence of an advantage of NALT with oral intake.

The third argument is price and dosage. Tyrosine is cheap, and one gram of NALT contains only about 0.8 g of tyrosine equivalent. To obtain the same amount of the amino acid, more NALT is needed, and it is usually more expensive.

Are there situations where NALT is justified? Its advantage is solubility, so it is more convenient in liquid forms, for example in ready-made drinks or soluble powders. But for capsules and tablets this has no practical significance.

How tyrosine was taken in studies

Tyrosine is a dietary amino acid, so it is appropriate to talk about doses here, but with reliance on the studied regimens. In the works, single doses were used ranging from about 2 g (Colzato et al., 2013) to 100–150 mg per kilogram of body weight (Banderet and Lieberman, 1989; Tumilty et al., 2011). For a person weighing 70 kg the upper limit of this range is over 10 g, which is much more than in a typical capsule.

Tyrosine was usually taken about 60 minutes before a stressful task or exertion, because it is precisely then that the plasma concentration approaches its peak. Taking it on an empty stomach or with a small amount of carbohydrates theoretically reduces competition with other large neutral amino acids for transport into the brain.

Prolonged daily intake at high doses has been studied worse than a single intake. Therefore the editorial team advises regarding tyrosine as a situational means — before a specific demanding day, a night shift or a competition in difficult conditions — rather than as a constant supplement.

Practical tips for those who have decided to try it:

• Start with a lower dose to assess tolerability: nausea and headache occur more often with large amounts.
• Do not take tyrosine in the evening — falling asleep may worsen.
• Do not combine it with several stimulants at once, so as not to increase tachycardia and anxiety.
• Assess the effect under real stressful conditions, not on a calm day.

Who should refrain

The most important limitation is monoamine oxidase (MAO) inhibitors. Combining tyrosine with them can theoretically cause a sharp increase in blood pressure, so such patients are not recommended tyrosine without a doctor's permission.

People with hyperthyroidism and those taking levothyroxine should be cautious, because tyrosine is a precursor of thyroid hormones. An interaction is also possible with levodopa, which is prescribed for Parkinson's disease: both substances compete for transport.

Also, tyrosine is not recommended for people with a history of melanoma (as a precursor of melanin it is theoretically undesirable), for pregnant and breastfeeding women — due to the lack of safety data. People with migraine should take into account that in some of them tyrosine may provoke a headache.

As for sports: tyrosine and NALT are not on the WADA Prohibited List. However, in pre-workout complexes tyrosine is often combined with stimulants, and it is precisely they that can become the cause of problems at doping control. Choose single-ingredient products or certified formulas.

Editorial conclusions

For most people considering tyrosine, the rational choice is classic L-tyrosine: it is better studied, does not require conversion and costs less. NALT makes sense only in liquid products, where solubility is important.

Realistic expectations — moderate support of cognitive function under stressful conditions: cold, sleep deprivation, multitasking. On a calm day, tyrosine will most likely change nothing.

The foundation of resilience to stress remains sleep, nutrition and training planning. Tyrosine is only a situational addition, and it should be tested on yourself carefully, taking into account medications and your state of health.

For more on the chemistry and absorption of both forms, read the article “L-Tyrosine or N-Acetyl-L-Tyrosine: What's the Difference.” We also recommend our materials on bacopa and ginkgo and on caffeine before competitions.

References

1. Jongkees BJ, Hommel B, Kühn S, Colzato LS. Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands — a review. J Psychiatr Res. 2015;70:50–57.
2. Banderet LE, Lieberman HR. Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans. Brain Res Bull. 1989;22(4):759–762.
3. Deijen JB, Wientjes CJ, Vullinghs HF, et al. Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course. Brain Res Bull. 1999;48(2):203–209.
4. Colzato LS, Jongkees BJ, Sellaro R, Hommel B. Working memory reloaded: tyrosine repletes updating in the N-back task. Front Behav Neurosci. 2013;7:200.
5. Tumilty L, Davison G, Beckmann M, Thatcher R. Oral tyrosine supplementation improves exercise capacity in the heat. Eur J Appl Physiol. 2011;111(12):2941–2950.
6. Magnusson I, Ekman L, Wångdahl M, Wahren J. N-acetyl-L-tyrosine and N-acetyl-L-cysteine as tyrosine and cysteine precursors during intravenous infusion in humans. Metabolism. 1989;38(10):957–961.
7. World Anti-Doping Agency. The World Anti-Doping Code: International Standard — Prohibited List. Montreal: WADA (чинна редакція).