Last updated on

What are the Benefits of L-Theanine Supplements?

Genes Mentioned

L-theanine is an amino acid found naturally in green and black tea, that boosts mood, and promotes a sense of calm without drowsiness.

L-theanine Health Benefits

There have been a number of studies looking at the benefits of L-theanine. The FDA considers L-theanine as a GRAS (“Generally recognized as safe”) supplement.

L-theanine as a calming agent

In the world of brain chemistry, glutamate is an “excitatory” neurotransmitter. You can think of glutamate as the brain’s gas pedal.

By contrast, GABA is the calming agent in the brain.

For more on the neurotransmitter balance in our brains, see our Cognitive Health and Genetics Page.

Glutamate and GABA are both essential neurotransmitters, with important roles to play in cognitive function, however, when glutamate levels get too high, as they can during times of prolonged stress, the usually beneficial glutamate can become what is called an excitotoxin.1

In fact, chronically elevated glutamate has been linked to a number of neurological diseases. 2

Glutamate antagonist

This study found that L-theanine reduces physiological and psychological stress by blocking glutamate receptors in the brain. One of the primary reasons people experience an anti-anxiety effect when taking L-theanine is due to this glutamate blocking activity. Put simple, L-theanine helps take your foot off the brain’s gas pedal by acting as a glutamate antagonist.

L-theanine may improve sleep

In a randomized, double blind study, theanine was shown to significantly improve sleep quality in boys with ADHD. 3

L-Theanine can boost some markers of immune function

This 2008 study found that L-theanine helped to prevent contracting the cold and flu and had an immune boosting effect “enhancing gamma-delta T cell function.”

The New York Times, reporting on the study, had this to say in summary:

Tea increases the body’s defenses against infection and contains a substance (L-theanine) that may be turned into a drug to protect against disease, a study has found. Coffee does not have the same effect, the researchers say in an article today in Proceedings of the National Academy of Sciences. A component in tea primes the immune system to attack invading bacteria, viruses and fungi, the study concluded. An experiment showed that immune system blood cells of tea drinkers responded five times faster to germs than did the blood cells of coffee drinkers.

Theanine increases alpha brain waves

Alpha brain waves are the creative centers of the brain.

Studies show L-theanine improves alpha brain wave function, even at low 50 mg doses meant to mimic “normal dietary levels.”4

L-theanine and allergy

L-theanine has shown some promise as a modulator of allergic reactions. 5

A major event in allergic reactions is the secretion of histamine from immune cells known as mast cells. Mast cells can be thought of as the first responders of the immune system, they are constantly sensing the environment and when they detect something potentially harmful they secrete a wide range of factors to kick start the immune response. When mast cells detect something as harmful (even if it’s harmless) this causes an allergic reaction. 6 L-theanine inhibits histamine release from mast cells.

Interestingly, this inhibition of histamine also ties in with L-theanine’s glutamate inhibitory activities. Histamine can induce glutamate release, which as we’ve established above, is an excitatory neurotransmitter our bodies need. 7 Excess histamine may cause an unhealthy build-up of glutamate, although there is some evidence that there is an upper maximum of glutamate build-up associated with histamine.

Not sure what to eat?

Gene Food uses a proprietary algorithm to divide people into one of twenty diet types based on genetics. We score for fat metabolism, histamine clearance, carbohydrate tolerance, and more. Where do you fit?

Learn More

L-theanine Side Effects

Low Blood Pressure and dizziness

L-theanine is contraindicated for those on high blood pressure medication because it lowers blood pressure further.8 Some people report episodes of light headedness after standing with repeated high doses of L-theanine.

Upset Stomach

There are many anecdotal reports of an overdose of theanine causing upset stomach in people experimenting with the supplement.

L-theanine biochemistry

So the interesting questions then becomes how does L-theanine link all these together, and is there a single gene or SNP which is of particular interest?

Lets look at histamine first, a major gene involved in histamine metabolism is AOC1, which encodes for the enzyme Di-amine Oxidase (DAO – pay attention to that abbreviation as it’s the cause of much confusion). In health DAO functions to break down histamine following its release from mast cells, curtailing the immune response. There are several SNPs within AOC1 which are associated with reduced DAO activity, resulting in histamine intolerance, which is characterized by symptoms often associated with allergy such as headaches, flushing of the skin and irritation.

The benefit of L-theanine here is clear. By suppressing histamine release from mast cells, it is prevented from building up to harmful levels, even in those with reduced DAO activity. 9

We’ve already described how L-theanine can inhibit stress by blocking glutamate receptors. As excess histamine can lead to the buildup of glutamate there’s a clear mechanism for impaired DAO activity leading to increased histamine, leading to increased glutamate. L-theanine works by both preventing histamine release, and also blocking glutamate activity as well.

L-theanine Dosage

Most supplements contain doses of between 50 – 200 mg.

Key Takeaways

L-theanine is a potent nootropic that is widely regarded as safe. Many benefits have been shown from supplementing with theanine with stress reduction leading most people’s lists.

Do keep in mind that theanine can interact with some drugs and may lower blood pressure to a level that will be uncomfortable for some.

As theanine crosses the blood brain barrier, also be on the lookout for changes in mood after high doses.

Dr. Aaron Gardner, BSc, MRes, PhD

Dr. Aaron Gardner, BSc, MRes, PhD is a life-scientist with a strong background in genetics and medical research, and the developing fields of personalized medicine and nutrition. Read his full bio here.

The very latest on genetics, nutrition and supplements delivered to your inbox!


Leave Comment

  1. Lori Mueller says:

    I’ve been using L theanine for a couple months now I take about 600 to 800 every day, along with beta blocker. Never felt so good, was able to stay off benzos forever.

  2. Norma says:

    I just starting taking l Theanine 200 mg in the morning for anxiety and 200mg at night for sleep. I am wondering about dosage. There seems to be no evidence about taking too much. Also does taking it every day enhance its effect eventually? Is there a major difference between l Theanine and Suntheanine?

    Thank you

  3. Silver says:

    Hi all,
    I hv read a few comments but there’s no reply by the administration.
    I want to enquire about the proper effective dosage of theanine I should go for while I’m on a hypertension medication coversyl 4mg. I’ve been feeling anxiety, fear & at times depression, phobia, panic as well. Having said that I m a hypothyroid patient and post menopause stage. Will await response.
    Thank u in advance.

  4. Nikki says:

    I’ve been researching L-Theanine on behalf of my son who has a bad stutter. He is 20 years old was hoping to “grow out of it”, but has not, it’s seems to be getting worse since he is in college and life stresses are increasing. I’ve read several articles about Theanine helping to curb the stuttering especially in stressful situations i.e. public speaking, presentations, etc. I also read that Thiamin and Magnesium together will also help the situation. IS there any harm in taking the 3 supplements at the same time or do you have any recommendations concerning this?

    • Nikki says:

      Update: my son has been taking all 3 of the supplements mentioned in my April 19th post for his stuttering for 2 weeks now…while he has not been “cured” by any means, we have noticed that he is stuttering less now but still has tough moments. He may increase his B1 (Thiamin) dosage to see if it helps reduce the stuttering even more. He has had no adverse reactions to taking any of these supplements together.

  5. Patti says:

    I have just recently developed anxiety and psnic attacks on occasion. Doctors
    Keep prescribing antidepressants which i can not take severe symptoms. Xanax .25 was prescribed 2-3 times per day. Yes it works but makes me tired and weak. I just started taking L-Theanine 100mg 2 xs per day. Works and stays in your system 8-10 hrs. While getting it in to my system i only take .125 xanax 3 times a day just to keep anxiety under control. I go to Vitamin Shoppe and purchase them. You can take up to 400 mg for moderate anxiety and more for severe. I have no side affects at all. Give it a try.

  6. Joshua says:

    Have to say, I agree with this article. I don’t know what I have, I’ve never gone to get it diagnosed, but I have trouble shutting down my brain. I think almost everything through that I am going to do, as well as thinking about what I need to do later, possible outcomes if things go this way or that, etc, and all going on at the same time. It gets noisy. Since i started on L-Theanine, I have been able to only hear what I want to from my mind, not have it all going like hundreds of tv screens in front of my face. I’m looking into trying GABA next, see if it will help too. One thing with me, I have found that Soy makes everything worse, up to the point where the fields around where I work are being harvested and I get furiously mad for no reason. I can think it through, see that I have no reason to be mad, but I can’t stop it, I feel ready to break things, rip them apart. I have only been using L-Theanine for about a month, so I don’t know how it will effect that, but I’m hoping it will help. Thanks for the write up!


Get the very latest on genetics, nutrition and supplements delivered to your inbox

Facebook icon Twitter icon Instagram icon Pinterest icon Google+ icon YouTube icon LinkedIn icon Contact icon Info icon Email icon Phone icon Pin icon
Back to top