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My experience with L-theanine: dose, benefits, side effects

Article at a Glance
  • L-theanine is an amino acid found in green and black tea.
  • Studies show that, even with 50mg doses mimicing normal dietary behavior, theanine increases production of alpha brain waves, which are the brain waves that increase creativity and decrease depression.
  • Theanine is a glutamate antagonist, meaning it blocks glutamate receptors in the brain, which is part of the reason some people report a calming effect after taking theanine.
  • Theanine has also shown promise as a sleep aid and in stopping the release of histamine from mast cells.
  • Despite efficacy at 50mg doses, many theanine supplements up this dose to 100mg and beyond, so keeping an eye on dose is important.
  • Also, be aware that some supplements that claim to have proven efficacy in studies, such as Alpha Brain, are really just piggy backing on previous theanine research showing theanine effective at increasing alpha brain waves at 50mg doses.
Genes Mentioned

If you’re researching L-theanine, also known as theanine, you may already know that it’s an amino acid, found in green and black tea, that boosts mood, and promotes a sense of calm without drowsiness. I will let Aaron get into the science of how L-theanine works to create these benefits later in this post, but before I do, I want to describe how I felt when I took L-theanine for the first time.

As you’ll see, it made me really nice to the people at Hertz rent-a-car.

Why I supplement with L-theanine

Please do not take this as an endorsement of her work on autism, of which I do not have an informed opinion, but I have found the the top level nutrigenomic theories outlined in Dr. Amy Yasko’s book Feel Good Nutrigenomics very useful. It was Dr. Yasko’s discussion of the glutamate/GABA ratio that first motivated me to use L-theanine as stand alone supplement.

Dr. Yasko believes the first step in crafting an effective health regimen is tackling imbalances in the glutamate/GABA ratio. 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, when GAD1 mutations are present, or on a high glutamate diet, the usually beneficial glutamate can become an excitotoxin. (R)

In fact, elevated glutamate has been linked to a number of neurological diseases. (R)

See also: The MSG in your supplements

L-theanine can help balance glutamate levels

Science Grade:

One of the supplements Yasko recommends to get glutamate levels under control is, you guessed it, theanine.

Here is what Dr. Yasko has to say on the issue:

Addressing imbalances in the glutamate / GABA ratio as well as the calcium to magnesium ratio is what I consider the starting point of this program.

Look to support with nutrients that help calm the nervous system including GABA, THEANINE, valerian root, pycnogenol, grape seed extract, resveratrol, and CoQ10.

Theanine is an important supplement for glutamate/GABA balance because it blocks glutamate receptors in the brain. (R) One of the primary reasons people experience an anti-anxiety effect when taking theanine is due to this glutamate blocking activity.

How L-theanine makes me feel

In a word, great. L-theanine gives me a calm, creative focus. I feel unrestrained by mental clutter and notice a marked improvement in mood.

For example, I was recently in San Diego, where I visit often, and was returning a Hertz rental car. When I returned the car, the people at Hertz ignored me for a very long time, taking their sweet time processing my car. This would have irritated me under normal circumstances (many years in NYC gives you this ridiculous sense of time when it comes to the performance of services, you want it now!). However, rather than indulge in a moment of self imposed stress, I waited patiently. When the Hertz man finally came over, I asked how his day was going.

I went into duck mode, water rolled off my back.

Overall happier, calmer, and less stressed. I felt a noticeable increase in creative energy. I normally have lots of ideas, but the increased focus allowed me to digest and organize, rather than feeling overwhelmed by all the things I wanted to create/ things I had to do.

As I used theanine over the course of a week, I found that it was also a meditation aide.

L-theanine and alcohol

Science Grade:

I have found that theanine can also be a fun supplement to take socially. I will normally take 100mg prior to a night of drinking as it can reduce the effect of a hangover, and adds to the relaxing effects of alcohol. (R) How does theanine reduce hangovers? It appears theanine speeds the metabolism of alcohol by helping the body produce glutathione, although the study we cite to here is in mice and not yet established. However, I can attest anecdotally to theanine being helpful at reducing the impact after a night of drinks.

Not an everyday supplement for some people

Science Grade:

Theanine produced solid benefits for me, both in work and socially, and I will definitely continue using it, however, it is contraindicated for those on high blood pressure medication because it lowers blood pressure. (R) When I’ve taken high doses for a number of days in a row, I have noticed a few episodes of light headedness after standing.

I wouldn’t recommend taking high doses of lumbrokinase, nattokinase or N-acetyl-cysteine alongside theanine, especially for lengthy periods of time.

Theanine will be a 1-2 times a week supplement for me, and potentially more frequently when I am looking to balance glutamate/GABA ratios.

L-theanine benefits – proven by studies

Ok, now we dig into some of the more noteworthy studies evaluating theanine.

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

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

This study found that L-theanine prevented 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.

This study found that L-theanine reduces physiological and psychological stress by blocking glutamate receptors in the brain. (R)

There are a few studies that show L-theanine improves alpha brain wave function, even at low 50 mg doses meant to mimic “normal dietary levels.” (R)

I am now passing the mic to Aaron for a deeper dive into how L-theanine works in the body.

L-theanine and allergy

Science Grade:

Thanks, John. L-theanine’s “mechanism of action” is quite interesting.

L-theanine has shown some promise as a modulator of allergic reactions. (R) 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. (R) Theanine inhibits histamine release from mast cells.

Interestingly, this inhibition of histamine also ties in with L-theanine’s glutamate inhibitory activities as well. Histamine can induce glutamate release (R), which as we’ve established above, is an excitatory neurotransmitter our bodies need. 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 (R).

L-theanine mechanism of action

Science Grade:

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 (R).

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

We’ve already described how L-theanine can inhibit stress by blocking glutamate receptors (R). 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.


There’s a nice indirect mechanism linking DAO, histamine and glutamate.

However, if you read around on the internet, you may find articles discussing a direct action for DAO interacting with glutamate. While there may be evidence linking them directly I’ve not come across it; rather I think it’s a case of confusing DAO the enzyme with DAO the gene. DAO is encoded for by the AOC1 gene and functions to breakdown histamine (R). There is however a DAO gene which confusingly encodes for an enzyme called  d-amino acid oxidase (DAAO), which is involved in glutamate metabolism (R).

See also: You say DAO, I say DAAO

Quite why it seemed a good idea for DAO to be encoded for by AOC1 and DAAO to be encoded for by DAO I’ll never know, but I think this is the basis for much confusion. So be careful when you’re trying to interpret your genetic results!

L-theanine Dosage

Ok, taking the mic back from Aaron for some closing thoughts.

I have found L-theanine to be an effective nootropic that produces a calm focus. For me, it’s an effective tool for writing, meditating, creative bursts, and even to unwind and get to sleep at the end of the day. I also like it socially.

If you’re using theanine as an anti-anxiety supplement, the calming effects for me were greatest when paired with GABA and valerian. Keep in mind that both GABA and valerian can upset the stomach, so start slow. I also don’t recommend this stack for daily use over extended periods of time, best to cycle on and off.

As we discussed, theanine lowers blood pressure. Because there can be side effects, I would encourage everyone to experiment with different doses to see what amount of theanine suits them best. Some will tolerate 200mg quite well, while others may want to dose more in line with the studies that used 50mg.

Choosing a theanine supplement

If you’ve read thus far and want to add theanine to your supplement stack, I’ve included a short section below that gives a tour around some of the best theanine products on the market, standalone supplements, as well as a couple blends that have positive reviews and are made with good manufacturing practices from brands I trust.

Theanine supplement comparison

Jarrow Formulas Theanine 100100mg L-theanine60/ct
Onnit Alpha Brain650mg Onnit Flow Blend (L-tyrosine, L-theanine, oat extract, phosphatidylserine), 350mg Cat's Claw bark extract, 240mg Onnit Focus Blend (L-alpha GPC, Bacopa extract, Huperzia serrata extract), 65mg Onnit Fuel Blend (L-leucine, vinpocetine, pterostilbene), 10mg Vitamin B690/ct
Jarrow Formulas GABA Soothe225mg Ashwagandha extract, 100mg GABA, 100mg Suntheanine30/ct

Jarrow Formulas Theanine

This is the theanine I take, although I take the 100mg capsules. Jarrow also makes a 200mg capsule if you find you do well with larger doses of theanine. In both cases, the capsules are easily broken apart so you can experiment with smaller doses. Remember, it’s the 50mg dose that triggered the increase in alpha brain waves in the studies, and the 50mg dose is also closer to what you’ll find in tea, but in today’s culture we assume that more is always better, which isn’t necessarily true. I will often take apart a 100mg capsule and empty out approximately 40-50mg so I have a conservative dose. Another advantage of the Jarrow products is they use a high quality theanine, called Suntheanine.

Alpha Brain by Onnit

Note: I don’t take Alpha Brain.

As a resident of Austin, Texas, I am perhaps more familiar than most with Onnit, the supplement brand started by Aubrey Marcus. You also may have heard of Onnit if you listen to the Joe Rogan podcast, as Joe has a stake in the company. Alpha Brain is one of Onnit’s top selling nootropic supplements, and it features a 200mg dose of theanine, along with a host of other ingredients, including tyrosine.

Reviews, both on the Onnit website, as well as on Amazon, are mixed, with some swearing by the product and others finding no benefit. Since Onnit adds tyrosine to the formula, efficacy may have something to do with the user’s dopamine receptor genes. We wrote a blog post on how genetics impact tyrosine metabolism, which I’d encourage you to read if tyrosine becomes a part of your supplement regimen.

I would also note that amino acids like tyrosine compete for uptake in the brain with tryptophan, which is the precursor to serotonin, so watch closely how this product makes you feel. For more on the impact of food and supplements on serotonin, see how to boost serotonin naturally and safely. As with standalone theanine blends, it’s best to cycle on and off of Alpha Brain, and be conservative with dosage.

I mention Alpha Brain in this post because I know they use quality ingredients, and because Onnit did a clinical trial that showed Alpha Brain improved alpha brain state, verbal recall and focus. Of course, this isn’t a big surprise because, as we know from theanine studies, theanine alone would likely have yielded all of these results, but nonetheless, conducting the trial is a sign of good faith and professionalism.

GABA Soothe by Jarrow

Note: I don’t take GABA Soothe.

But it is an interesting product because it blends theanine, GABA and ashwagandha, and adaptogenic herb used to promote relaxation. Now, you’ll remember, that for stress relief, I found theanine most effective when paired with GABA and valerian. This product adds GABA to the formula, as well as an herb that is popular with many people for reducing anxiety. The issue I see here is that the dose of GABA is very small.

There is a lot of controversy over whether GABA can cross the blood brain barrier as we know theanine does. Many say it cannot, however, in light of the fact that GABA moves out of cells much faster than it moves in, it may just be difficult to measure. For those who don’t need a large dose of GABA, this could be a product worth trying. However, as a point of reference, when I take GABA, I take a 750mg dose, which is 7 times higher than the GABA content of GABA Soothe.

John O'Connor

John O'Connor is the founder of Gene Food. He is passionate about nutrition, genetics, and wellness and uses this blog to publish self experiments as well as some of the research that the Gene Food team does internally to highlight stories of bio-individuality.

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Leave Comment

  1. Heather Jones says:

    Zen Theanine 255 mg is supposed to be taken without food.. but I’ve noticed that my stomach doesn’t feel good if I don’t eat with it… also.. I have motion sickness when I take this.. One of the ingredients in the capsule is sodium stearyl fumarate.. I read that it is an “Irritant”… Would I be better off finding L- theanine without the SSFumarate??… Or should I eat with it or??… I take this for anxiety and it is very effective for me!

    Cheers!.. Heather

  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!

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