L-tyrosine is a non-essential amino acid and a precursor molecule for different neurotransmitters in the brain. We’ve explored some of the biological effects of L-tyrosine in the body, the research highlighting the potential benefits and side effects, and recommended dosages.
What Is L-Tyrosine?
L-tyrosine, also known as tyrosine, is an amino acid. Amino acids are the building-block compounds that make up all of our proteins, hormones, and neurotransmitters. Amino acids can be divided into two separate categories:
- Essential amino acids: compounds that can’t be made in the body so need to be obtained from food
- Non-essential amino acids: compounds that can be made in the body so don’t need to be obtained from food
L-tyrosine is a non-essential amino acid and is made in the body by the addition of an oxygen molecule to the essential amino acid phenylalanine. It can also be obtained in pure form as a supplement and is found within certain foods including:
- Dairy products
L-tyrosine is a precursor molecule, meaning useful compounds inside the body are made from it. Some of the important substances made using L-tyrosine are:
- Dopamine: Dopamine is a neurotransmitter – a chemical messenger which carries and receives signals across the brain. Dopamine plays a role in increasing alertness, responding to and learning rewards, memory, and movement.
- Noradrenaline: Noradrenaline (also known as norepinephrine) is a neurotransmitter that responds to stress, increases attention, and plays a role in the immune system.
- Thyroid hormones: Hormones are chemical messengers which carry information around the blood to different organs. Thyroid hormones are responsible for the body’s metabolism.
- Melanin:: Melanin is a pigment that protects the skin from the sun.
What Are the Benefits of L-Tyrosine?
Improvement in Working Memory
Undergraduate students were given either an oral dose of L-tyrosine powder or a placebo in a study to examine the effects of L-tyrosine on working memory.
Students who took L-tyrosine performed better in a memory test than placebo, suggesting L-tyrosine increases working memory.
Working memory is the storage of temporary information and can be evaluated using an N-back task. The students who took L-tyrosine performed better in the N-back test than placebo, suggesting L-tyrosine increases working memory performance.
Another study investigated the effect of L-tyrosine on cognitive performance in participants who had lost a full night of sleep. The researchers showed that sleep loss caused the participants to perform worse on various cognitive tasks. However, if given L-tyrosine, the participants had reduced decline in cognitive performance.
Increased Cognitive Flexibility
L-tyrosine may also improve cognitive flexibility, as highlighted by a study showing L-tyrosine administration improved the performance of participants in a task-switching performance. Cognitive flexibility is the ability to switch between thinking about two different concepts and think about multiple things simultaneously.
May Help With Phenylketonuria (PKU)
PKU is a genetic disorder where people are unable to break down phenylalanine. This effect means people with PKU have a build-up of phenylalanine in the blood and brain, which increases the risk of brain damage.
As phenylalanine can’t be broken down into tyrosine, researchers have suggested that supplementing with L-tyrosine may be able to help improve some of the symptoms associated with PKU. However, the evidence is limited.
Possible Antidepressant Properties
Low levels of dopamine may be associated with some of the symptoms of depression, such as lack of pleasure and reduced motivation. As L-tyrosine is required to make dopamine, it could improve some of these symptoms.
One study showed that giving L-tyrosine to patients with dopamine-dependent depression successfully treated their depression for up to two years. However, other studies have shown L-tyrosine has no effect on improving depression in patients, indicating L-tyrosine may only be beneficial for specific types of depression.
Other Potential Uses of L-tyrosine May Include:
General recommendations are to take 100-300 milligrams of L-tyrosine per kilogram of body weight (mg/kg) per day, meaning people with a higher body weight may need to have a higher dose. Changes in working memory are notable after a 2-gram dose.
An experiment investigating toxicity in rats caused by repeated dosages of L-tyrosine showed that 600 mg/kg per day had toxic effects on the stomach and that 2000 mg/kg per day had toxic effects on the liver.
There is no evidence of serious adverse effects from L-tyrosine in humans. However, some common side-effects reported include:
Giving rats repeated high doses of L-tyrosine caused swellings in the stomach lining and changed the weight and shape of kidney and liver cells, suggesting that at high doses in humans, it may have toxic effects on the stomach, kidney, and liver.
L-tyrosine is broken down into tyramine – another amino acid that is also found in food. Certain antidepressant medications called monoamine oxidase inhibitors (MAOIs) block the breakdown of excessive tyramine in the body.
Combining L-tyrosine with tyramine-rich foods and MAOIs could lead to excess tyramine and unwanted side effects.
Because L-tyrosine increases tyramine in the body, combining L-tyrosine with tyramine-rich foods and MAOIs could lead to excess tyramine and unwanted side effects including high blood pressure and migraine.
L-dopa is a medication used in the treatment of Parkinson’s disorder (PD). Because L-tyrosine and L-dopa are both absorbed by the same receptors in the small intestine, taking L-tyrosine can decrease the effectiveness of L-dopa in PD treatment.
Bottom Line on L-Tyrosine
L-tyrosine is a non-essential amino acid that could have a variety of positive functions on cognition and in the treatment of certain disorders. However, at higher doses, it could have toxic effects and interact with certain medications.
Currently, the evidence for L-tyrosine benefits and risks is still very limited, but as research continues, more light may be shone on the positive and negative health outcomes.