What to Know About L-Theanine (2024)

L-theanine is a non-protein amino acid found in tea plants (Camellia sinensis L.) from which green and black tea are made. It's the main source of flavor in tea and has a caramel-like taste that reduces the bitter flavor of other compounds found in tea leaves.

In addition to being found in tea products, L-theanine can also be taken as a dietary supplement.

L-theanine is best known for its stress-relieving and anti-anxiety effects, but it may benefits health in several other ways, too.There are a few ways to take L-theanine to ensure safety and minimize any side effects.

L-theanine has antioxidant and anti-inflammatory properties as well as regulatory effects on anxiety and the immune system. Due to these properties, research suggests supplementing with L-theanine may benefit health in several ways.

Helps Reduce Stress and Anxiety

L-theanine has the ability to act on the central nervous system, influencing certain pathways and receptors in the brain to reduce symptoms of stress and anxiety.

L-theanine is able to cross the blood-brain barrier—a layer of cells between the brain's blood vessels and the brain tissue that prevents harmful substances from reaching the brain.

This means L-theanine can reach the brain to modulate neurotransmitters, which are molecules that send signals to different cells in the body. Specifically, L-theanine reduces the release of glutamate, an excitatory neurotransmitter that promotes these signals. During times of anxiety and stress, these signals can become hyperactive, so reducing glutamate may help regulate anxiety.

L-theanine also increases the release of γ-aminobutyric acid (GABA), and inhibitory neurotransmitter that blocks these signals. GABA is thought to help regulate anxiety, especially in people with anxiety disorders.

L-theanine also enhances the release of the anxiety-mediating compound dopamine and increases alpha-frequency brain waves, which is a pattern of brain activity associated with relaxation.

A review that included nine studies found supplementation with doses of L-theanine ranging from 200 to 400 milligrams (mg) per day may help reduce stress and anxiety in people exposed to stressful situations.

Other research shows supplementing with L-theanine in doses ranging from 200 to 400 mg per day for four to eight weeks may help improve symptoms of anxiety with minimal side effects.

Supports Restful Sleep

Due to its relaxing effects on the nervous system, L-theanine may help improve sleep quality.

A small study of 30 adults found participants who took 200 mg of L-theanine per day for four weeks experienced reductions in sleep latency—the time it takes to fall asleep. They also saw reductions in sleep disturbance and use of sleep medication compared to participants who took a placebo treatment.

A study of 160 people tested the efficacy of various supplements, including L-theanine, for their sleep benefits. Researchers found supplementing with 200 mg of L-theanine for seven days significantly improved sleep problems such as trouble falling and staying asleep.

Could Boost Cognitive Function

L-theanine directly impacts brain function, and study findings suggest L-theanine supplements may benefit memory and attention by improving the brain’s ability to focus and remember information.

A study including 69 Japanese adults between the ages of 50 and 69 showed a single dose of 100.6 mg of L-theanine improved reaction time and working memory on cognitive tests.

Additionally, a study of 32 healthy young adults found doses of L-theanine ranging from 100 to 400 mg significantly improved attention and information processing compared to baseline.

L-theanine also has neuroprotective properties, meaning it may protect brain cells from age-related damage and reduce the risk of cognitive conditions such as Parkinson's Disease. Green tea’s high content of L-theanine is thought to be a major reason why people who drink green tea regularly are at a lower risk of developing dementia.

May Improve Depressive Symptoms

L-theanine may help reduce depressive symptoms by modulating the activity of neurotransmitters, like dopamine.

A small study of 20 people with major depressive disorder (MDD) found supplementation with 250 mg of L-theanine for eight weeks significantly reduced symptoms of depression and anxiety. It also improved certain aspects of cognitive health, such as verbal memory and response time, compared to baseline.

Research also shows L-theanine may have a positive effect on symptoms related to mental health disorders such as schizophrenia and schizoaffective disorder.

While these findings are encouraging, it’s important to discuss supplement use with your healthcare provider before using L-theanine for mental health disorders like depression.

How to Take L-Theanine

L-theanine is available in several forms, including pills, liquids, capsules, and powders.You can also get some L-theanine by drinking certain green or black teas.

L-theanine can be taken on its own or in combination with other calming substances. For example, L-theanine is commonly combined with magnesium, a mineral thought to help regulate stress.

L-theanine can be taken at any time of day, including in the morning to help support healthy stress response and at night before bed to promote restful sleep.


Dosing of L-theanine varies, but most studies have used doses ranging from 100 to 400 mg per day. Higher doses of L-theanine have been safely used without adverse side effects.

The amount of L-theanine found in teas may vary depending on when and where the tea is sourced and how the tea is brewed. Green, black, white, and oolong teas typically contain about 5-7 mg of L-theanine per gram of tea.

L-theanine has been shown to be safe, even when taken in high doses. It’s generally well-tolerated and is not associated with health risks or side effects.

However, L-theanine may not be safe for people who are pregnant or breastfeeding, or people who have low blood pressure. L-theanine may lower blood pressure levels, so it could cause blood pressure to drop too low.

Drinking high amounts of L-theanine-containing teas that are caffeinated could cause side effects like headaches, dizziness, and a racing heart beat. Most people can safely consume about 400 mg of caffeine per day.

Potential Drug Interactions

There is some evidence L-theanine supplements may lower blood pressure. If you take one or more medications to lower blood pressure, you may want to avoid taking L-theanine.

Due to its relaxing and sleep-supporting effects, L-theanine may also have an additive effect with some sedative medications.

Avoid taking supplements containing D-theanine as it may prevent the absorption of L-theanine in the body.

Talk to your healthcare provider before starting a new supplement, especially if you take one or more medications.

What to Look For

When shopping for an L-theanine supplement, it’s important to choose high-quality products from trusted supplement brands.

Whenever possible, purchase L-theanine supplements that have been third-party tested by organizations like ConsumerLab and NSF International, which set strict standards for supplement quality and safety.

It’s also important to choose supplements you can easily tolerate. If you have difficulty swallowing pills, you may want to purchase a liquid or powder L-theanine supplement.

Can You Take Too Much L-Theanine

L-theanine isn’t known to be toxic and hasn’t been shown to have any adverse effects on health, even when taken in high doses.

However, it's best to follow the dosing instructions listed on the supplement product.

If you are drinking teas for L-theanine, drinking more than 400 mg of caffeine per day may cause side effects. One eight-ounce cup of tea may contain 14-60 mg of caffeine.

Side Effects of L-Theanine

L-theanine supplements haven’t been associated with any side effects.

However, drinking large amounts of L-theanine-containing caffeinated tea could lead to symptoms like headaches, dizziness, and a racing heart. Too much caffeine may also lead to anxiety and trouble sleeping.

L-theanine is an amino acid that is concentrated in tea and can also be taken as a dietary supplement. It has calming effects on the body and may help reduce stress and relieve symptoms of anxiety and depression.

L-theanine supplements may also help promote restful sleep and improve certain aspects of cognitive function, like attention and memory.

Supplements of L-theanine are considered safe and aren’t associated with any side effects. However, it’s important to talk to your healthcare provider before starting a new supplement to ensure it's safe and appropriate for your specific health needs.

What to Know About L-Theanine (2024)


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