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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.

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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.

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Leave Comment

  1. John boy says:

    Is it ok to take a Gaba supplement with L- theanine and if so what is a good starting dose and ratio?

  2. Sheryl says:

    I can’t thank you enough for this article. Great info; such useful tips. Please keep us updated. I cut and pasted the whole thing into a Word document so I would have it to refer back to, in case you ever take your site down!!

    Again, thank you for the time and effort put into this.


  3. Sierra says:

    Wonderful article with such helpful information. Thank you! Has anyone experienced building up a tolerance to L-Theanine after several months of use? I’ve been taking 300 mg during the night in order to stop morning adrenaline rushes and it worked like a charm. It reduced them enough to allow me to wake more normally and to even sleep in if I wanted to. It also had a positive lingering effect for a few hours after getting up. But the effects seem to be lessening lately and I’m now getting full-blown adrenaline rushes again with no change in diet, supplements, lifestyle, stress level, etc. I’m curious if this has happened to anyone else. Thanks.

  4. Dana Evans says:

    I’ve been taking 100mg at bedtime to improve my quality of sleep ….and it does. It also seems to increase the quality and frequency of dreams ( increased time in REM?) It TOTALLY stopped the insane swelling from histamines every time I consumed alcohol ANNNND…..no hangover!!! It may be reason i have not experienced brain fog in awhile. Mine are a small fruit flavored chewable. Idk about lowering blood pressure. I’m not seeing that or maybe it has a short half life?

  5. Rick Mosqueda says:

    I have anxiety and have tried many things for it nothing seems to work I went to the doctor two weeks ago and as we talk he said it seems like I don’t have anxiety I have a d d h and referred me adderal and that’s also not working can you please help me I’m thinking of taking L- Theanine for my anxiety how much milligrams should I start off with I’m very desperate please help and a good brand name that I can buy at CVS Walmart or wherever it’s sold please let me know ASAP I’ve even tried kratom but I don’t like that stuff it helps a little but it tastes like crap please respond ASAP thank you so much Rick

  6. Lauri says:

    You mentioned you wouldn’t take NAC and L-theanine alongside for an extended period of time, ….”I wouldn’t recommend taking high doses of lumbrokinase, nattokinase or N-acetyl-cysteine alongside theanine, especially for lengthy periods of time.”
    Would you please explain in detail, why not? I am a 53 yr old female, 96 lbs and currently take NAC (500mg) once per day. I just found out about l-thenine and have been taking 100 to 200
    mg per day in addition. I’m now concerned – please inform.

    • Hey Lauri, my thoughts are that it might not be a great idea to take blood thinning supplements alongside a supplement that has the potential to lower blood pressure.

      • Lauri says:

        Thank you for responding so quickly and for the information. I’ll see if I can find out if the amount of each I’m taking would put me at any risk.
        And I just saw I left the ‘a’ out of Theanine…

      • Wendy says:

        I switch off between serrapeptase and lumbrokinase for Lyme. And, because they have to be taken on an empty stomach, this means 9.30 p is my dosing time. My doctor has me taking one or two 100 mg l-theanine chewables for sleep, which I do at 10 p. I RARELY sleep through the night, and wake up to severe tinnitus at 2am. Then I pop another l-theanine to hopefully fall back asleep. Sometimes this works. And sometimes not. Any suggestions? Sleep has become a fleeting fancy. Sigh.

  7. Greta says:

    I’m very thankful to come across this article. What we share is a kind of anxiety which is part of our DNA. No matter how much we focus on meditation, relaxation, yoga and healthy lifestyle in general…. of which all of these have been part of my life on a daily base. Still I need to supplement with extra’s of something besides the above. Nine years ago I had a terrible breakdown of sleeplessness ..no matter what I changed on my diet or lifestyle…doctor after doctor visits brought me to the point of diagnoses ‘Restless Leg Syndrome’. I was very surprised to hear this verdict …and still after these years I doubt this is what I have! But I was put on medication Rivotril ..(0,5 mg), since then hooked on it. I know the Rivotril since long isn’t doing the trick anymore as many other drugs you need to increase the dosage to get the effect it had as when started. (…but haven’t done this!… too scared of this level 5 medication)
    I have started to take L-theanine for the last couple of days … I have slept like a baby and hope that the adoption or habituation doesn’t kick in after taking it for a couple of weeks?? (I’m taking 150mg an hour before sleep) But at this moment I’m raving about L-theanine.

  8. Irene Kittrell says:

    If green tea “primes the immune system against bacteria, etc.” does it also prime the immune system of people with an autoimmune disease, thereby making it worse?

    • Jason says:

      Not sure yet. I supposedly have vitiligo, and AA. Only on second day of dosing. I have had anxiety and worries that the vitiligo maybe caused by something else other than the so called autoimmune disorder. So far it has helped me with my anxiety. I am curious to see what it does for my white patches, if anything. As a side note I have my suspiscions of bacteria, fungus, or parasite as with any problem. I am curious myself. See in a month or so. Still dosing various mg. 200 and higher.

      • Krissy says:

        Jason – This is a few months after your comment- so not sure you’ll see this. But just in case – here goes: Was your Vitiligo affected in anyway after taking Theanine for awhile? I just started this week and I love the diff in how I’m feeling. But / I’ve had vitiligo for a little over 10 years now.

        I’m just curious to know what – if any- differences you experienced?

        Thanks 😀

  9. Anna says:

    I was recommended to give this to my son who was recently diagnosed with ADHD and has been taking 27mg of Ritalin with only negative side effects and no benefit. He noticed an improved feeling of his overall mood (and I noticed as well) in taking L-Theanine for 1 day – 200mg which was recommended by his psychiatrist – along with magnesium, B-6, 12, zinc & Inositol but I haven’t added those in yet. What I’m confused about is all the discussion around the different brands of L-Theanine. Jarrow, Nature’s Trove, Nutricost, etc. How can the brand impact it’s effect if that is the main ingredient and same dosage is given?

    • Danielle says:

      I too, wondered the same thing. I work in a pharmacy and never questioned different manufactures, or brands vs. generics. However, I came across it in an Amazon review where someone had wondered why one brand was substantially greater in cost versus every other brand. Someone had commented that specific brand actually made the ingredient, opposed to the other ones which contained the ingredient derived from the plant? It was a while ago and I don’t remember the specifics and tried to find it again with no luck.

      How old is your son that you give this to? I wanted mine to try it but I don’t know if he is too young. However, I feel that everyone could benefit from this.

    • Danielle says:

      I really hope this helps him and he can get off of the ADD prescriptions. I hate that they prescribe them for children, they are a serious controlled substance. Unfortunately, so many drugs are pushed by doctors and approved by the FDA with worse side effects and detrimental results, and we have no choice but to trust our health care professionals and believe they and the FDA have our best interest in mind.

      • Lisa says:

        Has anyone taken the supplement Zen 200mg? A single dosage contains 550mg of GABA and 200MG L-Theanine. My integrative/functional doctor wants me to start taking 1 per day and then work up to 2 a day. I’m currently taking 5MG of Valium to help with the dizziness/spinning from a vestibular disorder and autonomic nervous system disorder. I don’t know if Zen will interact with the Valium and I have to be careful bc my blood pressure can go low or high. I would greatly appreciate any comments/suggestions.

  10. Danielle says:

    I wish I would’ve found this years ago. Funny, the doctors don’t recommend this and push all the other drugs with terrible side effects.

    I ordered Natures Trove brand from Amazon based on the reviews but didn’t notice the benefits until I started taking Finest Nutrition brand from Walgreens.

    I find myself taking a few doses during the day as I can feel agitation arising. Im sure it can’t be good, but have yet to read anything about too-high of doses.

  11. Benette says:

    Can i give this to my child that has ADHD to lessen his hyperactivity and poor sleep? If yes,
    what will be the recommened dosage. Thank you in advance.

  12. Ron says:

    l-theanine while blocks AMPA and the other glutamate receptor it is an agonist of the NMDA receptor. and it increases glutamate neurotransmission via blocking the glutamate transporter.

  13. Marie says:

    I have aaib and am on medication for it. I have had 2 tia”s and normally cant drink caffeine so I am wondering if theane will cause palpitations

  14. Laura says:

    Hi, I’ve just started looking into Theanine to help manage my anxiety symptoms. The only kind I could find at my local health store though was 400mg doses. Is this too high? They’re capsules, could I break them open at take half at a time or would that screw with how it’s absorbed?

    Also, would taking Theanine clash with my regular antihistamine (loratadine)? I have grass, animal and dust allergies so I usually take 2 a day in summer and 2-3 times a week in winter.

    • Dana says:

      I take 100mg theanine every night at bedtime with 50mg benadryl and sometimes add 100-200mg quercitin ( natural antihistamine) if I’m itching ( having some transient histamine weirdness)….and no issues for me. There was about a week where I added allegra-d to that regimen the next a.m. and no issues there either. I know none of those are loratadine but if you want to be certain ask your pharmacist or maybe a drug interaction checker on the internet. I LOVE it and have gotten many different benefits from it.

  15. David says:

    Maybe I’m looking at it wrong. Isn’t a proper histamine response something that is beneficial, though? If the mast cells are supposed to be responding to allergens or invaders, Isn’t blocking the histamine response effectively suppressing the immune system?

    With that said I took L-Theanine (SunTheanine) last night for the first time, the day after my ativan prescription ran out. I was going through some anxiety effecting sleep, and couldn’t sleep without at least a small piece of ativan.
    The Theanine really did seem to make me relaxed, and I fell asleep surprisingly easily and slept through the night.

  16. JoAnne says:

    GREAT and informative article and I sure hope L-thenanine helps me sleep a full night. In addition to numerous physical injuries that required titanium implants, I also suffered Traumatic Brain Injury (TBI) all from a bicycle accident 2 1/2 years ago. One of the ongoing issues from the TBI is that often my brain only shuts off for 2 to 3 hours of sleep each night which then renders my brain deficient in allowing me to properly walk, talk, or process thoughts the following day. I do not and will not take sleep medication and have tried a number of natural, plant based supplements, none of which have helped.

    My problem and question is as follows; I have very low blood pressure (92/58 and occasionally lower), are there any studies that claim L-theamine causes low blood pressure to go even lower? I am on a vegan diet and foods that are considered to help lower blood pressure have never affected my blood pressure and I’m hoping L-theamine is the same.

    Thank you for any information you can provide. I NEED a full night sleep to get this damaged brain healed,

    • Dale Hoover says:

      Hello JoAnne, – I am a 72 year old female who has had low b.p. all my life (usually around 96/54); I just recently discovered L-theanine for sleep, as I too only can sleep 2-3 hours, then can’t get back to sleep (adult-long scenario) without taking a whole lot of vit. C (it acts as an anti-histamine), or taking an anti-histamine pill. Last night I took 200 mg. L-theanine at bedtime & after waking I got back to sleep(!), – plus even had dream recall! Tonight I will do the same. I believe the warning about low b.p. and theanine is for ppl who are taking b.p.-lowering meds.

  17. Joanna says:

    Is there any research on mixing theanine with Klonopin? I am currently using klonopin to help take the edge off my intense anxiety/agoraphobia.

  18. Tyler says:

    I’ve tried many different known supplements over the years that don’t seem to positively help anything in the end. However, that is not the case with Theanine. It’s absolutely amazing. I’ve been using it daily for a couple of years and have never had any side effects at all whatsoever. It really calms my nerves and anxiety. Not massively like you’re drugged. Just a gradual soft calm starts to ease through me where I’m suddenly not bothered by much when I would be easily aggravated or explosive before taking this. So this definitely is compatible with me. I stumbled upon this article as I was curious if others had the same experience because no one talks much about theanine. They talk about antidepressants, but this is just as good without the side effects. Of course as should be understood everyone’s physical and brain chemistry is different. Just because this is fantastic for me doesn’t mean it will be for you. You’ll have to find out for yourself and what dosage is right. Too little might not do anything, but the too much can bring up side effects.

    • Travis says:

      ” Just a gradual soft calm starts to ease through me where I’m suddenly not bothered by much when I would be easily aggravated or explosive before taking this. ”

      I just started taking L-theanine today, it arrived in the mail.

      About a week ago I started taking tongkat ali 200:1 extract which I noticed increased testosterone, confidence, reduced anxiety.

      I was making some food today and I dropped the spoon on the floor, which normally would have pissed me off but something different happened in my mind. I grabbed another spoon and was totally fine.

      Normally little things like that I find really annoying. Weird to explain but I think the combo of tongkat ali and l-theanine is pretty good.

      • Lynn says:

        How much Thianine do you take mg wise a day please?
        I’ve been taking 300mg mornings and 150mg at night, but no idea how much to take!

  19. Gurps says:

    Great article! I’ve more confidence to take Theanine.
    What type of diet would be looking at to complement this? Its almost impossible to avoid glutamate as its in everything. However, there are supplements such as B6 and Taurine which convert glutamate tonGABA so maybe we don’t need to be as restrive?

    • Really tough to say on diet without knowing a lot more, but if you do supplement with B6, be sure to use very small doses. Large doses of B6 can cause nerve damage.


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