People use L-tyrosine to boost cognition, mood, and thyroid hormones, especially when they’re under stress. However, research says it may do the opposite and worsen mental health in some cases. Read on to discover both sides of L-tyrosine supplements and learn what the evidence suggests.
What is L-Tyrosine?
The “Cheese” Amino Acid
L-tyrosine is a naturally occurring form of tyrosine, an amino acid the body uses to make proteins, neurotransmitters, and other vital compounds .
We don’t depend on food sources of tyrosine since we can make it from another amino acid, phenylalanine; this makes tyrosine a non-essential amino acid. Still, you can ensure its optimal levels by eating a variety of tyrosine-rich foods such as [2, 3]:
- Cheese and dairy
Did you know? Scientists named tyrosine after cheese (Greek: tyros), where they discovered it.
L-tyrosine is a popular nootropic supplement; people use it to boost cognition and alertness under stress. It’s used alone or combined with other ingredients in protein and pre-workout supplements.
However, l-tyrosine supplements have not been approved by the FDA for medical use. Supplements generally lack solid clinical research. Regulations set manufacturing standards for them but don’t guarantee that they’re safe or effective. Speak with your doctor before supplementing.
- May boost cognition and alertness under stress
- May improve mood
- May increase thyroid hormones
- May help with fibromyalgia
- May cause headache and anxiety
- May worsen cognition in the elderly
- Interacts with L-DOPA and thyroid medications
- May not help with depression and attention disorders
- May not improve physical performance
- Long-term safety unknown
Roles and Functions
In the body, tyrosine acts as a precursor to neurotransmitters called catecholamines :
People use L-tyrosine under stressful conditions that are more likely to deplete catecholamines.
N-acetyl-L-tyrosine (NALT or NAT) is more water-soluble than L-tyrosine and thus more suitable for intravenous nutrition for people who can’t eat and drink .
As a nutritional supplement, our bodies supposedly use it better than L-tyrosine, but the evidence tells a different story. We metabolize only 25% of NALT into free tyrosine and eliminate 35-38% with the urine [9, 10, 11].
In a study of 13 subjects, N-acetyl-L-tyrosine didn‘t increase tyrosine levels at all .
Thus, L-tyrosine remains a better option for oral supplementation.
L-Tyrosine Health Benefits
People with an inborn metabolic disorder – phenylketonuria (PKU) – are unable to break down phenylalanine properly. In turn, the buildup of phenylalanine causes brain damage and cognitive impairment [13, 14, 15].
Tyrosine is a component of medical foods for people with phenylketonuria.
These patients should follow a special low-protein diet to minimize the intake of phenylalanine. Additionally, they should add tyrosine as a component of medical food. This reduces the risk of tyrosine deficiency since the body converts phenylalanine into tyrosine.
On the other hand, L-tyrosine supplementation for PKU may sound reasonable, but a Cochrane Database review of six clinical trials failed to confirm its benefits .
2) Cognitive Performance and Alertness (from Stress or Sleep Deprivation)
A review of 15 clinical trials investigated the effects of L-tyrosine loading – short bouts of higher doses – on cognition and behavior. This dosing pattern prevented catecholamine depletion and boosted mental function in stressful and demanding situations .
It showed the best results in people exposed to:
- Multitasking and distractions [22, 23, 24]
- Sleep deprivation [25, 26]
- Harsh military training [27, 28]
- Cold weather [29, 30, 31]
Additionally, L-tyrosine may not improve cognitive performance under normal conditions. In older adults, L-tyrosine loading even produced the opposite effects – worsening memory and cognitive function .
No valid clinical evidence supports the use of L-tyrosine for any of the conditions in this section. Below is a summary of up-to-date animal studies, cell-based research, or low-quality clinical trials which should spark further investigation. However, you shouldn’t interpret them as supportive of any health benefit.
3) Thyroid Hormones Balance
In 85 volunteers, supplementation with high doses of L-tyrosine (12 g daily) during harsh winter slightly increased T3, the active thyroid hormone. It also greatly reduced TSH, high levels of which are linked with hypothyroidism and stress .
Tyrosine supplementation prevented thyroid hormone drops in mice exposed to chronic stress .
Patients with narcolepsy struggle to stay awake during the day. They often experience cataplexy (sudden muscle weakness with intact awareness) and sleep paralysis .
In a study of 10 patients, L-tyrosine improved only three of more than 20 tested symptoms. The patients felt less tired and more alert .
A group of doctors managed to handle daytime sleep attacks and cataplexy with L-tyrosine in eight patients. They kept using this approach in other narcolepsy patients after the initial success. This study was limited by its open-label design, small sample, and a lack of placebo controls. It doesn’t allow for a definite conclusion .
5) Addiction and Substance Withdrawal
Dopamine plays a central role in the brain’s reward pathway. Scientists first thought that it makes certain things (such as food and sex) enjoyable. New research suggests dopamine actually doesn’t make us feel pleasure, it makes us want it. People with addiction may be depleting or over-sensitizing this pathway, which increases their cravings and drug-seeking behavior .
- Anger and hostility
- Suppressed vigor
6) Weight Loss
Many supplements are promoted to stimulate weight loss, but none of them has yet been supported by strong clinical evidence and approved by the health authorities. A healthy, calorie-controlled diet and increased physical activity remain the only proven strategies for weight control .
Tyrosine supplies catecholamines and thyroid hormones, which both enhance metabolism and energy production. For this reason, many people want to know if L-tyrosine can boost weight loss.
No other trials have documented the benefits of L-tyrosine for weight loss.
7) Attention Disorders
In a clinical trial, L-tyrosine improved attention in eight of 12 participants with attention deficit disorder over two weeks. However, after six weeks, all patients developed a tolerance to the treatment, and their improvement stalled .
L-tyrosine supplementation provided no benefits to 7 children with ADHD .
Impaired production of dopamine and noradrenaline may trigger attention disorders, and such cases may be more likely to benefit from tyrosine supplementation .
Combination With Adderall
L-tyrosine helps restore catecholamines, and some people combine it with Adderall to “lessen the side effects.” However, this combination should be avoided. No studies have verified its safety and efficacy and potentially dangerous interactions are possible.
8) Mood Improvement
Evidence is lacking to support the use of L-tyrosine in people with depression and mood disorders, but L-tyrosine from dietary sources may contribute to mental health.
According to some scientists, imbalances in brain neurotransmitters play a role in depression and other mood disorders. Since tyrosine enables the production of dopamine and noradrenaline, it may act as nutritional mood support .
Limited evidence suggests it may be beneficial for particular mood disorders such as:
- Depression due to low dopamine 
- Low mood from living in harsh, cold environments [54, 36]
- Depression after childbirth 
However, the above results stem from small clinical trials, some of which lacked placebo controls. A larger trial of 65 patients failed to verify the antidepressant effects of L-tyrosine .
L-Tyrosine Side Effects and Precautions
This list does not cover all possible side effects. Contact your doctor or pharmacist if you notice any other side effects. In the US, you may report side effects to the FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch. In Canada, you may report side effects to Health Canada at 1-866-234-2345.
According to the FDA, L-tyrosine is “generally recognized as safe” (GRAS) .
High doses (100-200 mg/kg) caused cognitive decline in older adults .
Supplement-drug interactions can be dangerous and, in rare cases, even life-threatening. Always consult your doctor before supplementing and let them know about all drugs and supplements you are using or considering.
L-tyrosine competes for brain uptake with L-DOPA, a drug for Parkinson’s disease. Tyrosine supplements and even tyrosine-rich foods may hinder the transport of L-DOPA into the brain; this can lead to variations in the treatment response, known as the “on-off” phenomenon [59, 60].
Patients with Parkinson’s disease are often deficient in tyrosine hydroxylase – an enzyme that converts tyrosine to L-DOPA – which is another limitation for tyrosine supplements .
High doses of L-tyrosine (12 g daily, for 4 months) can increase thyroid hormones. People with an overactive thyroid and those taking thyroid medications may want to avoid it .
L-Tyrosine Dosage & Supplements
L-tyrosine supplements have not been approved by the FDA for medical use. In general, regulatory bodies aren’t assuring the quality, safety, and efficacy of supplements. Speak with your doctor before supplementing.
The doses used in clinical trials may not apply to you personally. If your doctor suggests using a grape seed extract supplement, work with them to find the optimal dosage according to your health condition and other factors.
For short-term cognitive enhancement, L-tyrosine was used 30-60 mins before a stressful or challenging task. Benefits for depression, fibromyalgia, and attention disorders usually took 1-4 weeks [21, 53, 40, 46].
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Do not consider user experiences as medical advice. Never delay or disregard seeking professional medical advice from your doctor or another qualified healthcare provider because of something you have read on SelfDecode.
Most products contain 500 mg of L-tyrosine per pill. People who need long-term supplementation with higher doses usually buy bulk powders.
Users take L-tyrosine to boost their mental clarity, alertness, and focus. A smaller number has reported success with depression, sugar cravings, and alcohol withdrawal.
Combinations with antidepressants and other supplements such as 5-HTP are popular for mood disorders. However, this is dangerous and should be avoided at all costs. Never combine drugs and supplements before consulting with your doctor.
Other users experienced no benefits for cognition and mental health; some of them even said their mood and focus worsened. The most common side effects are anxiety, headache, and insomnia. Users also suggest starting with lower doses to see how your body will react.
L-tyrosine is an amino acid that builds proteins, neurotransmitters, and thyroid hormones in the body. Its best dietary sources are protein-rich foods such as cheese, meat, eggs, and beans.
People supplement with L-tyrosine to boost cognitive performance and alertness when they’re under stress, which is supported by limited evidence. It likely doesn’t help with depression, attention disorders, and physical performance.
L-tyrosine supplementation may cause headaches, anxiety, and nausea. Pregnant women, children, and people taking L-DOPA or thyroid hormones should avoid it unless prescribed by a doctor.