Introduction to Tyrosine

Tyrosine is a neutral amino acid meaning it is a building block for proteins. It can be found in many high-protein foods such as cheese, chicken, and eggs.

In the body, tyrosine is mainly used in the brain as a precursor to a class of neurotransmitters called catecholamines.

The three major catecholamines that tyrosine can become are dopamine, norepinephrine, and epinephrine. These catecholamines are used in many different cognitive functions.

To become a catecholamine, tyrosine requires two transformative steps. First off, it must be converted into dihydroxyphenylalanine (DOPA). Then, an enzyme (usually some form of a decarboxylase) will turn the DOPA into one of the three catecholamines.

Tyrosine is a Precursor to Neurotransmitters

Tyrosine is a precursor to neurotransmitters which include dopamine, norepinephrine, and epinephrine. [R]

Elevated levels of tyrosine can increase production of these neurotransmitters during situations in which neurotransmitter synthesis is increased. [R]

However, these situations had to be sufficiently challenging to require extra release of neurotransmitters and subsequent depletion of these neurotransmitters. To maintain optimal neural performance, tyrosine supplementations were seen to prevent the neurotransmitters from depleting. [R]

1) Tyrosine Replenishes Cognitive Resources Used in Memory


Tyrosine supplements were seen to restore certain cognitive resources used to increase working memory. [R]

Working memory is responsible for the continued updating and maintenance of memory. [R]

Studies showed that tyrosine only replenishes certain cognitive resources when the resources get used up, so only challenging situations that require the use of these cognitive resources will see an enhancement of the cognitive resources. [R]

2) Tyrosine Supplementation may Increase Levels of Thyroid Hormones

Regulation of thyroid hormones is vital for well-being as thyroid hormones are responsible for regulating the energy metabolism in the body, aiding in the repair and renewal of damaged cells, and increasing resistance to constant stress [R].

In a bird study, chicks with induced tyrosine deficiencies had much lower levels of T3 and T4, common thyroid hormones, in their blood [R].

Birds that were given only phenylalanine supplements, which is the direct precursor to tyrosine, did not gain as much weight as birds given phenylalanine plus tyrosine supplements. This evidences that tyrosine supplementation helped in the growth of the chicks [R].

In rat studies where certain rats were put under constant stress, the stressed rats showed a decrease in T3 and T4 thyroid hormones. This is due to a decrease in the enzymes thyroid peroxidase and oxidase, which are crucial for thyroid hormone production. Many depressed patients become stressed due to the loss of the T3 and T4 hormones [R].

Supplementation with tyrosine increased levels of the neurotransmitter, norepinephrine, which acts on different neurological pathways in the brain to cause the release of thyroid hormones. The tyrosine-supplemented rats not only gained less weight, but also performed significantly better in maze tests and distance traveled [R].

3) Tyrosine Increases Dopamine Levels in the Brain

Tyrosine supplementation increases dopamine levels in the striatum of the brain when animals are given treatments that increase dopamine demand. [R]

Tyrosine administration also increased dopamine levels in the extracellular fluid of the brain. However, this effect was short-lived as the extra levels of tyrosine were seen to activate mechanisms in the brain which slowed neuronal firing. This, in turn, brought the dopamine levels back to the original levels before tyrosine administration. [R]

4) Tyrosine Helps Combat Stress

Tyrosine is a precursor to norepinephrine and stress can reduce norepinephrine levels in the brain  (locus coeruleus, hippocampus, and the hypothalamus) [R]

Rat studies showed that when rats were subjected to shock, norepinephrine levels dropped heavily, but when tyrosine was injected into the rats, the norepinephrine levels remained constant. This is most likely caused by the fact that tyrosine enhanced the rate at which norepinephrine was produced in stressful situations. [R]

The added tyrosine caused the rats to showcase no behavioral deficits while rats that did not get the tyrosine supplements did show behavioral changes resulting from stress. [R]

It is also hypothesized that tyrosine may improve physical performance only if the exercise being done produces enough cognitive stress and depletes dopamine or norepinephrine levels. [R]

5) Tyrosine may Improve Attention Deficit Disorders


Clinical trials of using tyrosine to try improving attention deficit disorder symptoms in humans showed some positive results. Of the 12 adults that volunteered for the clinical trials, eight of them showed some form of clinical improvement in two weeks. [R]

However, after six weeks, all eight of the patients developed a tolerance to the tyrosine and improvements stalled. Further investigation into how tyrosine may be used to cure attention deficit disorders needs to be done. [R]

Impaired neurotransmitter metabolism may be a predisposition for attention deficit disorder [R].

Although this only accounts for 5-10% of the attention deficit disorder cases, it is more likely that such cases would benefit more from tyrosine supplementations. [R]

6) Tyrosine may be Used to Treat Depression


Tyrosine was found to help depression in certain patients in some clinical trials. A single case, placebo-controlled, case for a 30 year old woman suffering from depression showed marked improvement after tyrosine therapy. [R]

Placebo treatments immediately showcased a return of depression symptoms. Continued tyrosine therapy brought back a marked improvement. [R]

Further trials regarding two other patients with depression also showed improvements in symptoms. [R]

However, larger clinical trials of 65 patients did not support that tyrosine can be used as an antidepressant. [R]

This can be attributed to the fact that depression is dependent on a wide variety of factors, not simply a lack of dopamine or norepinephrine. Tyrosine as an antidepressant could possibly be used for patients in which the depression is stemming from low dopamine and norepinephrine levels. [R]

7) Tyrosine may be Used to Treat Parkinson’s


Nine patients who had Parkinson’s were treated with tyrosine and probenecid. These patients showed an increase in homovanillic acid in the cerebrospinal fluid. The presence of homovanillic acid, a product of dopamine metabolism, correlates to the fact that dopamine is being released in the brain. [R]

Because Parkinson’s is strongly linked with the degeneration of neurons that release dopamine, increased levels of homovanillic acid could be good proof that tyrosine may be used to treat the disease. [R]

8) Tyrosine Decreases Unwanted Action Tendencies

Studies have shown that when patients get tyrosine administered, they will be better at reducing unwanted tendencies. [R]

The study describes these tendencies as inhibitory control. When patients were asked to perform a stop-signal task (where the patient clicks stop when a green arrow turns red), patients with tyrosine injections were seen to do better than those with a placebo. [R]

9) Tyrosine Improves Mood

When patients were subjected to stressful conditions such as the cold or elevated altitudes, increased tyrosine levels were seen to better patient’s moods. One of the reasons for this betterment was due to lowered symptom intensities. [R]

In a long term study, patients in Antarctica were given tyrosine supplements daily over the summer and winter. However, only during stressful conditions in the winter did the tyrosine supplements work to increase mood (by 47%). [R]

Summer conditions were not harsh enough to illicit a response. [R]

Side Effects of Tyrosine Supplementation

1) Tyrosine Supplementation may Reduce Energy

Although many users state that tyrosine supplementation has benefited them tremendously, some other users have noticed a constant tired state that follows tyrosine supplementation. People take tyrosine supplements sometimes to help their tiredness, but in some cases, it actually made them more tired [R].

2) Tyrosine Supplementation may Cause Stiffness in Shoulders and Neck

One user on tyrosine supplementation noticed stiffness in his/her shoulder and neck area. Other reviewers noticed similar side effects and agreed with that user [R].

3) Tyrosine Supplementation may Lead to Weight Gain

One user noticed that tyrosine supplementation led to unwanted weight gain. Three other reviewers corroborated this side effect [R].

Synergies with Other Supplements

Users of tyrosine supplements have also seen major improvements when using with other supplements. Some users that use tyrosine to fight depression have noticed improvements when using tyrosine supplements along with 5-HTP, a tryptophan supplement. This is because 5-HTP increases serotonin in the brain while the tyrosine increases dopamine and norepinephrine, which all have to do with increasing mood [R].

The user mentions that other antidepressants like Prozac only increase serotonin, so tyrosine supplementation can help with increasing the release of other neurotransmitters [R].

Another user suffering from fatigue and low adrenal output also used the tyrosine supplement along with 5-HTP and found similar beneficial effects [R].

Combining the tyrosine supplements with a Super Cortisol supplement from Now Foods’ has helped another patient suffering from fatigue. The user mentions that energy levels have increased and that brain fog has disappeared after combined usage [R].

However, drug mixing should always be done under the supervision of a doctor. Please consult with your local physician before combining any supplements.

Drug Interactions

1) Tyrosine Interferes with the Uptake of Parkinson’s Drug (L-dopa) into the Brain

Tyrosine supplementation may actually interfere with the treatment of Parkinson’s disease [R].

A common occurrence in the disease is the “on-off” phenomenon where levodopa is not as well absorbed or transported at times [R].

During the “off” times of the disease, the patients are barely able to or cannot walk at all or accomplish their everyday tasks necessitating the need for a constantly “on” treatment [R].

Studies of nine patients showed that when amino acid-rich meals were taken, the levodopa concentrations in the blood decreased by 29% and the absorption was delayed by 34 minutes [R].

This happens due to the competing nature of levodopa and tyrosine into the brain. Higher levels of tyrosine can reduce the transport of levodopa into the brain reducing the effectiveness of the treatment [R].

2) Tyrosine Supplementation with Thyroid Hormone Pills may Lead to Overload of Thyroid Hormones

Tyrosine supplementation leads to an increase in thyroid hormones [R].

If this supplement is taken along with thyroid hormone pills, the body may produce too many of the hormones and cause unwanted side effects. Thyroid hormones control a wide range of bodily processes such as regulating the energy metabolism in the body, aiding in the repair and renewal of damaged cells, and increasing resistance to constant stress, so excessive hormones may damage the body’s ability to perform these tasks [R].

Please consult a professional before taking tyrosine supplements when using other drugs.

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  • jon miller

    one of the best things for thyroid problems,try it,you will be glad you did,helps with depression

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