Side Effects of L-Tyrosine

L-tyrosine is an ordinary amino acid from protein food, and in studies at doses up to 150 mg/kg of body weight it was generally well tolerated. However, a supplement is a concentrated intake of a single substance that can affect catecholamines and thyroid hormones. Our editorial team has examined which side effects of tyrosine are described, who it is contraindicated for and which drugs it cannot be combined with.

General safety profile

Tyrosine differs from many supplements in that a person gets it daily from food: meat, fish, eggs, dairy products, legumes, soy and cheese are its main sources. So the substance itself is not foreign to the body, and the mechanisms of its metabolism are well known.

In controlled studies on healthy people, tyrosine was given in single doses of about 100-150 mg/kg of body weight, as well as in courses of several grams per day over days (Jongkees et al., 2015; Deijen et al., 1999). No serious side effects were reported in these works, and adverse reactions were usually mild.

At the same time, when developing amino acid intake norms, the US Institute of Medicine was unable to establish a tolerable upper intake level for tyrosine due to a lack of data (IOM, 2005). This does not mean that any dose is safe; it means that the long-term safety of high doses has not been sufficiently studied.

So the key conclusion is: a single or short intake at research doses in healthy people looks acceptable, but long-term intake of large doses and intake by people with certain diseases or on certain medications requires caution.

The most common side effects

Most adverse reactions to tyrosine are linked either to the direct effect of a large amount of the amino acid on the digestive system or to its role as a precursor of catecholamines.

• Gastrointestinal discomfort.Nausea, heartburn, a feeling of heaviness - especially when taking a large amount of powder on an empty stomach.
• Headache.Mentioned in user reports and some studies; the mechanism is not fully understood.
• Sleep disturbances.Taking it in the evening is associated in some people with difficulty falling asleep, which is logical given the role of noradrenaline in the state of wakefulness.
• Restlessness, irritability.Occur rarely, more often in combination with caffeine and other stimulants.
• A feeling of palpitations.Described occasionally, mainly as part of pre-workout complexes that contain stimulants.

It is important to understand that in pre-workout complexes tyrosine is almost always combined with caffeine, synephrine and other stimulants. So some of the "side effects of tyrosine" described by users can actually be explained by other components of the formula.

Regarding blood pressure, the data do not indicate an increase in healthy people. Moreover, in the study by Deijen et al. (1999), systolic pressure in cadets on tyrosine even decreased compared with the control group. However, people with hypertension on constant treatment should act with caution, especially when combining it with stimulants.

Most of these effects are minimized by simple actions: reducing the dose, taking it no later than the first half of the day and avoiding the simultaneous combination of several stimulating substances.

Dangerous interactions with medications

The most serious risks of tyrosine are linked not to it itself but to its combination with certain drugs. It is precisely these interactions that our editorial team considers the most important part of the safety topic.

The interaction with MAO inhibitors is a classic caution for substances that concern catecholamine metabolism. MAO enzymes break down dopamine, noradrenaline and tyramine. When they are blocked, additional "raw material" for catecholamines can theoretically contribute to an undesirable rise in blood pressure. Despite the fact that tyrosine and tyramine are different substances, the conservative approach is to avoid such a combination.

Regarding levodopa: tyrosine, phenylalanine, leucine and other large neutral amino acids compete with the drug for transport (Fernstrom, Fernstrom, 2007). Large doses of amino acids can reduce the effectiveness of treatment. That is exactly why patients with Parkinson's disease often have even their protein diet adjusted on a neurologist's advice.

Regarding thyroid hormones: in a healthy person the synthesis of thyroid hormones is controlled by the pituitary gland and iodine availability, so additional tyrosine has little effect on it. However, in patients with thyroid disease or on hormone therapy, any changes should be coordinated with a doctor and monitored with tests.

If you take any psychotropic, neurological or endocrine drugs, be sure to consult a doctor before using tyrosine.

Who tyrosine is contraindicated for

Besides drug interactions, there are several conditions in which taking tyrosine as a supplement is unacceptable without a doctor's oversight.

1. Hereditary disorders of tyrosine metabolism (tyrosinemia).The body cannot break down tyrosine normally, so additional intake is contraindicated; the nutrition of such patients is controlled by doctors.
2. Hyperthyroidism and Graves' disease.Because of tyrosine's role in the synthesis of thyroid hormones, caution is advisable.
3. Melanoma or a history of melanoma.Tyrosine is a precursor of melanin; the risk is theoretical, but many sources advise refraining.
4. Pregnancy and breastfeeding.There are insufficient data on the safety of concentrated supplements.
5. Childhood and adolescence.Only as prescribed by a doctor.

Separately about phenylketonuria: in this case tyrosine is not contraindicated but, on the contrary, is conditionally essential, and it is obtained as part of special therapeutic formulas. However, the dosage is determined only by a metabolic physician, and self-administration of supplements is inadvisable.

People with migraine should keep in mind that headache is one of the described side effects. Although there is no direct evidence of provoking attacks, it is reasonable to start with a minimal dose and monitor how you feel.

People with pronounced anxiety or panic attacks also require caution, especially in combination with stimulants: the effect on catecholamines can theoretically worsen the symptoms.

How to minimize the risks

For healthy people who do not take medications and do not have the listed conditions, the risks of tyrosine can be reduced to a minimum with a few simple rules.

First, start with the minimal dose indicated by the manufacturer and assess tolerability over a few days. Research doses of 100-150 mg/kg are already high amounts, so switching to them right away is not advisable. We write about dosing in more detail in the material on the practical intake of tyrosine.

Second, take tyrosine in the first half of the day or 30-60 minutes before a cognitively or physically demanding situation. An evening intake increases the risk of sleep problems.

Third, be careful with combination products. If tyrosine is part of a pre-workout complex, check how much caffeine and other stimulants are in it. The total dose of stimulants is often more important for safety than tyrosine itself.

Fourth, use tyrosine situationally - on days of special load - rather than continuously for months. There are few data on the safety of long-term intake of high doses, so this approach is reasonable from the standpoint of caution.

Editorial conclusions

L-tyrosine at research doses is generally well tolerated by healthy people. The most common side effects are stomach discomfort, headache, sleep disturbances with evening intake and restlessness, especially in combination with stimulants.

The most serious risks are linked to interactions: with MAO inhibitors, thyroid hormones and levodopa. Tyrosinemia, hyperthyroidism, melanoma, pregnancy and breastfeeding are grounds for refraining from the supplement without consulting a doctor.

Situational intake, moderate doses and attention to the composition of combination products are the basis of safe use.

We also recommend the articles "How to Take L-Tyrosine: Dosage, Timing, Duration," "L-Tyrosine: What It Is and How It Works" and "The Benefits of L-Tyrosine for Athletes: The Evidence Base."

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. 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.
3. Fernstrom JD, Fernstrom MH. Tyrosine, phenylalanine, and catecholamine synthesis and function in the brain. J Nutr. 2007;137(6 Suppl 1):1539S–1547S.
4. Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: National Academies Press; 2005.
5. Banderet LE, Lieberman HR. Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans. Brain Res Bull. 1989;22(4):759–762.
6. 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.