What Does L-Theanine Do?

by Kat Austin November 23, 2022 6 min read

What Does L-Theanine Do? - Vida Optima™

L-theanine supplements are flying off the shelves, and you can find this little gem added to wellness drinks, nootropic stacks, and more. The question is–what does L-theanine do that makes it so special? The answer is in how L-theanine interacts with the body’s nervous system–by mimicking the action of the body’s primary amino acid.

To help you better understand, let’s dig into the L-theanine’s function and potential benefits:

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Key Takeaways

  • L-theanine is a naturally occurring amino acid found in tea and certain mushrooms.
  • It may interact with nervous system functions to promote calmness, focus, and healthy sleep cycles.
  • L-theanine is safe and no toxicity has been reported.
  • You may want to pair it with other supplements to create synergistic wellness stack.
A bowl of L-theanine powder and some L-theanine capsules to show examples of forms of L-theanine that can be used for supplementing.

What is L-Theanine?

L-theanine is just recently stepping into the wellness world spotlight, but you may already know more than you thought about L-theanine and it’s many potential benefits. That is, you may already be familiar with the benefits associated with certain teas, like green tea, which is one of the primary natural sources of L-theanine (along with some superfood mushrooms.)

L-theanine is one of the primary amino acids found in tea leaves at a concentration somewhere between 0.9-3.1% of the dry weight of the leaves, which translates to about 25-60mg in a 6 ounce serving of tea (made with approximately 2.5g of dried tea leaves). Aside from adding to the savory, bold flavor of most teas, it’s thought to have a few therapeutic benefits, acting both as a nootropic (cognition enhancing) and adaptogenic (stress regulating) compound.

What does L-Theanine do in the body?

So, how exactly does L-theanine work to provide these benefits?

L-theanine, which is formally known as L-g-glutamylethylamide, is absorbed by the small intestine and promptly crosses the blood brain barrier, where it can interact with the nervous system. L-theanine is quickly absorbed in the small intestine, crossing the blood-brain barrier, and delivering protective effects to nerve cells.

L-Theanine is related to glutamine, the body’s primary amino acid. Glutamine is thought to heavily impact the production and function of the body’s three main neurotransmitters–GABA, serotonin, and dopamine. Dopamine and serotonin are the “happy hormone” and GABA plays the important role of helping to inhibit nerve signals involving fear and stress.

In a healthy case, the body produces plenty of glutamine on it’s own, but stress, injury, exhaustion, and other outside factors can cause the body to need more glutamine than it can produce.

So, L-theanine supplementation may help to boost the body’s production of important neurotransmitters similarly to glutamine. That means that when stress or exhaustion run their course, L-theanine can help the body keep up. As an amino acid that the body can absorb and use, L-theanine may supplement many bodily functions, leading to an array of potential health benefits, like:

  • Help regulating stress
  • Mood support
  • Promoting relaxation without causing drowsiness
  • Supporting healthy sleep cycles
  • Balancing the effects of caffeine to promote alertness without many of caffeine's side effects

Read “L-Theanine Benefits” to learn more.

Let’s look at the research available:

L-Theanine Benefits and Research

Although most human trial sample sizes have been small, L-theanine is often considered a nootropic, or a “smart drug” that enhances brain performance. A comprehensive 2016 review found that L-theanine may help improve cognitive performance overall. In this text, L-theanine supplementation was linked with improved focus, reaction times, and alertness. A small 2011 study also found that L-theanine had a pronounced effect on attention and reaction time response in healthy adults who are prone to anxiety.

A woman sitting at her desk to focus on work after taking L-theanine capsules

One study involving 91 people found that a combination supplement of green tea extract (360mg) and theanine (60mg) helped to improve selective attention in subjects with mild cognitive impairments (such as ADHD). The authors of this study (and others) believe that a combination of caffeine and L-theanine provide more benefits than just using L-theanine on it’s own.

That 2016 comprehensive review also suggests that L-theanine could boost certain immune functions that help fight off disease. Some reports also describe L-theanine to have adaptogenic benefits, meaning they help the body deal with stress. For instance, a 2019 randomized controlled trial involving 30 healthy adults found that daily L-theanine supplementation decreased stress-related symptoms (involving depression, anxiety, and sleep) and increased cognition scores (involving verbal fluency and executive function). Ultimately, the authors concluded that L-theanine was safe and well-tolerated and may be a “suitable nutraceutical ingredient for improving mental conditions in a healthy population.”

According to a 2018 study L-theanine may also help to improve sleep quality. In this study, participants who suffered from conditions that disrupt sleep (like depression and anxiety) reported better sleep quality after taking up to 900 mg of L-theanine daily for up to 8 weeks.

How to Use L-Theanine

If you’re sold on L-theanine’s benefits and interactions in the body, you’re probably wondering how to best use it to you advantage. L-theanine supplements are pretty popular, and you can usually find L-theanine in various dosages and forms, like as capsules or powder. Plus, it’s often an ingredient used in nootropic blends, so you may be able to find an L-theanine supplement that also offers other nootropic compounds, like 5-HTP, Alpha-GPC, or Lion’s Mane.

How much L-theanine should I take?

The actual amount of L-theanine you should take depends on unique factors like your weight, age, diet, and health effects you hope to achieve. You may need to start with smaller doses of L-theanine and increase your dosage overtime until you experience the full benefits.

Also keep in mind that L-theanine is sold as a supplement in the U.S., which means that the dosage size is not standardized. You should pay close attention to the dosage of any product you choose.

On average, people take between 100-500 mg of L-theanine daily, and the total dosage may be divided into three smaller doses taken throughout the day.

You may find that you need less L-theanine to experience the full benefits if you have a diet that’s high in theanine sources, like green and black tea and certain types of mushrooms.

Read “L-Theanine Dosage” to learn more.

When’s the best time to take L-theanine?

If you’re taking L-theanine with caffeine, you’ll probably want to take it first thing in the morning, or at least 6 hours before bed. However, for L-theanine supplements without caffeine, when you take them is less important than how often you take them.

Feel free to work in your L-theanine doses whenever works best for you–just choose a time that makes it easy to remember to take L-theanine every day because most of the benefits are due to a systemic effect that takes place over time.

How long does L-theanine take to work?

In most studies, subjects took L-theanine for a period of 2-8 weeks to evaluate the benefits. You may start to see benefits after the first week, but it may take two weeks or more to experience the complete benefits that L-theanine can offer.

Is L-theanine safe?

L-theanine’s overall benefits look too good to be true–what’re the drawbacks? That’s the best part–there are virtually no downsides to supplementing with L-Theanine. In fact, no toxicity levels have ever been reported, and there is no evidence to suggest that it can cause and tolerance-building or dependency, so it’s a perfect option for daily dosing.

Keep in mind that many L-theanine supplements have caffeine. When taking large doses of caffeine, with or without L-theanine, you may experience side effects like nausea, upset stomach, or frequent urination.

Conclusion: How Does L-Theanine Work?

To sum things up, L-theanine mimic glutamine, an amino acid that regulated the production of the body’s most important neurotransmitters. Over time, taking L-theanine supplements may help you feel relaxed, improve how you handle stress, promote focus, and help improve your sleep. If you want to take L-theanine every day, you may consider looking for a nootropic stack with L-theanine, or taking L-theanine with caffeine for increased benefits.


  1. Research Breakdown on Theanine https://examine.com/supplements/theanine/research/#ref-10
  2. “l-Theanine as a Functional Food Additive: Its Role in Disease Prevention and Health Promotion” https://www.mdpi.com/2306-5710/2/2/13/htm
  3. “Effects of l-theanine on attention and reaction time response” https://www.sciencedirect.com/science/article/pii/S1756464611000351
  4. “A combination of green tea extract and l-theanine improves memory and attention in subjects with mild cognitive impairment: a double-blind placebo-controlled study” https://pubmed.ncbi.nlm.nih.gov/21303262/
  5. “Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6836118/
  6. “L-theanine in the adjunctive treatment of generalized anxiety disorder: A double-blind, randomised, placebo-controlled trial” https://pubmed.ncbi.nlm.nih.gov/30580081/

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