L-Theanine: Benefits, Side Effects & Dosage

What is L-Theanine?

If you’ve enjoyed a cup of tea lately, you may have gotten part of your daily dose of L-theanine.



L-Theanine Benefits

Boosts Calming Brain Chemicals

L-theanine is naturally present in the human body; a non-protein amino acid that helps deliver nerve impulses to the brain. It derives its existence from natural glutamine, and it also shares some of its effects. L-theanine boosts calming brain chemicals, which include:

GABA (gamma-aminobutyric acid) – This inhibitory neurotransmitter puts a “brake” on the excitatory neurotransmitters that want to you to “fight or flee.” GABA has a major role in reducing those excitable neurotransmitters and is found all over the brain.

Dopamine – Versatile dopamine is both an excitatory and an inhibitory neurotransmitter. It’s associated with reward systems and motivation.

Serotonin – This inhibitory neurotransmitter is connected with mood and emotions. Serotonin balances and regulates the sleep cycle, food digestion, carb cravings and pain control.

These neurotransmitters orchestrate productive sleep, alertness, mood, energy, appetite, focus and other cognitive functions. L-theanine is responsible for heightening their levels, promoting the kind of relaxation found in… well, a good cup of tea.


Histamine – This excitatory neurotransmitter takes part in responding to foreign body invaders (like allergens) with an inflammatory reaction.

Acetylcholine – Found throughout the nervous system, this neurotransmitter stimulates muscles, including those of the gastrointestinal system and autonomic nervous system.

Epinephrine – Epinephrine, also called adrenaline, is produced by the adrenal glands. Its job is to prepare your body for danger by increasing your blood pressure, heart rate and production of glucose. When you think of epinephrine or adrenaline, think “fight or flight response.”

Enhances Alpha Brain Waves

Alpha brain waves are the elements that are circulating around in your head when you are being creative, meditating, daydreaming or experiencing REM sleep. L-theanine triggers these alpha brain waves, promoting relaxation. L-theanine relaxes without a sleepy, sedated feeling or a crash later in the day.

Other Benefits

Stress & Anxiety Relief

L-theanine is an anxiety and stress reducer — it can lower heart rate and blood pressure. According to a study in 2016, several participants divided into groups consumed a drink containing 200 mg of L-theanine or a placebo. One hour after consuming the drink, they were tested for their response to a cognitive stressor. In the group receiving the L-theanine, the stress response was greatly reduced. Three hours after drinking it, a stress hormone in the saliva was tested and the L-theanine group had a significantly lower level of the stress hormone.


Increased Focus, Memory & Learning

When the body deals with stress, it produces those excitatory “fight or flight” hormones. When the body is flooded with these brain chemicals, it becomes preoccupied, and sensible brain functions like memory forming and learning are temporarily set aside. This is why people who live with chronic anxiety often see their cognitive functions reduced. L-theanine can restore a sense of calm and boost the ability to relax, think and avoid stressful feelings that inhibit maximum learning.

Besides this, L-theanine promotes an increased attention span. In fact, one study showed that individuals taking L-theanine combined with caffeine did better on a test of accuracy, making less errors. L-theanine and caffeine used in combination has been studied, and the findings show that when these chemicals partner together, they seem to help people process visual information and move effectively between tasks. A study completed in 2013 found that L-theanine and caffeine together helped a group focus during demanding tasks given to them. They also reported feeling more alert and less fatigued in general.

Better Immunity

Because L-theanine acts as an antioxidant, it reduces the existence of free radicals that rove around the body, causing inflammation, tissue breakdown or degeneration. Findings show that L-theanine may improve the immune system.

Fights Cancer


More interesting correlations about the benefits of tea and L-theanine are being examined, though these studies are not conclusive.

A number of studies suggest that regular tea drinkers have lower rates of cancer than non-tea drinkers.

One study determined that tea-drinkers were 37 percent less likely to develop pancreatic cancer.

ovarian cancer

Japanese scientists followed more than 40,000 adults for nine years. There was a positive correlation with these subjects as a group: when their tea drinking increased, the incidence of liver cancer decreased.

A study involving over 69,000 older adults over a span of eleven years found that drinking a few cups of tea per day reduced all types of digestive cancers by 11%.

A study in Japan focused on 472 women recovering from a breast cancer diagnosis. Those who drank the most green tea had the least likelihood of recurrence.

Blood Pressure Control

A study done in 2012 observed individuals who regularly experienced higher blood pressure after specific mental tasks. The study found that L-theanine reduced the blood pressure increase in this group of people. Caffeine was also tested with similar, but less beneficial results.

Sleep Quality Improvement

A known relaxer and stress reliever, it makes sense that L-theanine can also help people fall asleep more easily at bedtime. Without being a sedative, the natural properties of L-theanine can lower anxiety and promote a healthier, better quality sleep for many.

In two specific groups of people, studies confirm that L-theanine promotes sleep improvement:


L-theanine may help those diagnosed with schizophrenia sleep better.


Sinusitis Relief

Sinusitis is a common ailment — especially during the cold winter months. The sinuses — those small, hollow cavities behind your cheekbones, are lined and can become inflamed by a virus. The sinuses are lined with cilia — those little hair-like strands that move mucus along within the nose. When an individual is plagued by a sinus infection, the cilia get stagnant and do not clear the nose of infected mucus. When the infected mucus thickens, the bacteria multiply there.

So how does L-theanine assist the sinuses? L-theanine can actually boost the cilia movement in the nose.  Drinking a cup of green tea seems to spur those cilia on to action, doing their job to sweep the mucus down into the stomach, where they can be destroyed by the stomach acid.

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Helps Maintain Healthy Weight

L-theanine can help maintain a healthy weight by promoting relaxation and squashing stress. By inducing a calming effect, it reduces the need to seek the boost of serotonin via guilty pleasures.

L-theanine also promotes healthy weight by assuring a more relaxing sleep. Getting better sleep and maintaining better sleeping habits can strengthen the immune system and enhance cognitive performance. Studies show that diminished sleep levels increased hunger levels.

L-Theanine Supplement & Dosage

It’s estimated that the content of L-theanine in green tea is about 1-2 percent of the weight of dry tea leaves. This comes to approximately 25-60 mg of L-theanine. Even a daily level of 50 mg of L-theanine has a noticeable effect on mental alertness. When precise doses are necessary, it’s best to take a capsule or tablet instead of tea, since the L-theanine levels can vary.

L-theanine supplements are available as capsules and tablets; doses range between 50 and 200 mg. Some people take the following daily doses of an L-theanine supplement:

For sleep, stress and other uses — 100-400 mg L-theanine

Combined with caffeine — 12-100 mg. L-theanine + 30-100 mg caffeine

A safe, easy way to get a good dose of L-theanine is through a daily cup of tea. L-theanine is found in large amounts in green tea, but also found in white tea and black tea.

L-Theanine Side Effects

In the United States, L-theanine has been given the label GRAS (generally recognized as safe). L-theanine supplements are usually tolerated well with no harmful effects. However, pregnant and nursing mothers should avoid using the supplement.

People with the following specific situations should consult their health practitioner before taking L-theanine:

low blood pressure

Children under the age of 18

high blood pressure

People taking stimulants

The Bottom Line

People have counted on their daily cup of green tea for centuries. Whether you are a tea-drinker or not, you can benefit from the relaxing, health-promoting influence of L-theanine.

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