What is L-Theanine & Should You Be Taking It? Here's What Experts ...

Available as a supplement and in some foods, L-theanine is an amino acid that may have some health benefits.

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Reviewed by Dietitian Jessica Ball, M.S., RDReviewed by Dietitian Jessica Ball, M.S., RD

L-theanine is a nutrient found in some plants and supplements. It has gained popularity for its potential health benefits, particularly related to stress relief and improved sleep. We spoke with registered dietitians to get the full scoop on L-theanine, from benefits and side effects, to who should take it and who should avoid it.

Related: Is L-Glutamine Good for Your Gut? A Registered Dietitian Weighs In

What Is L-Theanine?

L-theanine is a non-protein, water-soluble amino acid known for its potential to promote relaxation and ease stress without causing drowsiness. It is found naturally in plants like matcha, green, black and white teas, and fungi like some mushrooms. It is also available in supplement form, typically as a pill or powder.

Potential Health Benefits of L-Theanine

While L-theanine is best known for helping people relax, it may have other potential health benefits as well.

Promotes Relaxation and Relieves Stress

According to Kelsey Costa, registered dietitian nutritionist and founder of Dietitian Insights, “L-theanine may have significant therapeutic effects on mental health, such as reduced depression and stress and improved emotional and cognitive function.”

Studies show that L-theanine helps lower stress-related symptoms, improve sleep quality and promote cognitive function in both healthy individuals and those with major depressive disorders. Athletes and other individuals under stress have also reported improved performance and reduced stress responses when using L-theanine.

May Increase Focus and Attention

L-theanine may enhance attention, focus and cognitive performance. It may be even more effective when combined with caffeine, which can help improve memory and executive function, and reduce distractions and mind wandering. L-theanine might also be beneficial for people with ADHD because it supports sustained attention and impulse control. However, more research on this topic is needed to clarify the relationship, especially for kids and young adults.

Supports the Immune System

L-theanine has antioxidant, immunoregulatory and anti-inflammatory properties. Studies suggest it may decrease the instances of respiratory infections, aid in flu prevention and decrease inflammation in the digestive tract.

“It's important to note that many of the available studies on potential health benefits have small sample sizes, show limited improvements and often involve healthy individuals rather than those with chronic health problems,” says Emily Haddock, RD, LDN, registered dietitian and owner of Music City Nutrition & Wellness. Additional research is needed on more diverse populations to further clarify and support these benefits.

Related: 4 Supplements You Shouldn't Take for Immune Health, According to Dietitians

Potential Side Effects of Taking L-Theanine

“With the small bit of research currently available, there aren't many confirmed side effects or direct risks associated with taking L-theanine,” Gabbie Ricky, M.S., RDN, performance nutrition specialist, tells EatingWell.

“As with any supplements you're considering, however, make sure you purchase from a reputable manufacturer. Look for supplements that have the Good Manufacturing Practices (GMP) certification and have been rigorously third-party tested for product quality and purity,” she adds.

Related: 7 Things You Should Look for When Buying a Supplement, According to Dietitians

Some side effects associated with L-theanine are often due to the overconsumption of caffeine by those who increase L-theanine intake by drinking tea. These side effects may include:

• Headaches

• Nausea

• Jitteriness

• Irritability.

The recommended daily intake of caffeine is 400 milligrams or less.

Who Should Take L-Theanine?

“People who regularly work in high-risk environments or under high levels of stress may benefit from the potential cognitive benefits of L-theanine, such as improved focus especially when paired with caffeine,” says Ricky. “Some examples of these populations might include professional athletes, tactical athletes (like firefighters, military personnel, etc.) and healthcare workers,” she adds.

People with poor sleep quality, depression and anxiety might also benefit from L-theanine, but it's important to talk with a healthcare provider before adding any new supplements to your routine.

Who Should Avoid It?

While L-theanine is safe for most people, some should avoid it. “People who are pregnant or lactating should avoid L-theanine as it has not been adequately tested in these populations,” adds Haddock.

People who take medications for high blood pressure may need to avoid L-theanine, as it may further reduce blood pressure.

Also, anyone receiving chemotherapy for cancer treatment should avoid L-theanine supplements until after their treatment course is complete. “In supplemental doses, the potent antioxidant function of L-theanine may reduce the efficacy of certain chemotherapy drugs,” Ricky tells EatingWell.

It’s always recommended to speak with a healthcare provider before adding any new supplements to your routine, particularly if you are undergoing treatment for cancer or high blood pressure.

The Bottom Line

L-theanine is a non-protein amino acid that is found in some foods like tea and mushrooms. It is also available in supplement form. Many people may be able to safely take L-theanine without negative side effects, but some people (like those who are pregnant or undergoing cancer treatment) should avoid it. While L-theanine shows promise of potential health benefits, more extensive research is needed on larger and more diverse populations to confirm this.

Frequently Asked Questions

Is it safe to take L-theanine every day?

Based on current information available, most healthy adults can take L-theanine daily without negative health consequences or side effects. Generally, it's safe to drink tea and take supplements containing L-theanine every day. However, talk to your doctor before starting to make sure it’s safe for you.

Does L-theanine make you sleepy?

L-theanine may improve sleep quality by reducing stress and promoting a sense of calm. It isn’t usually associated with sleepiness or drowsiness during the day, but may contribute to better sleep at night.

What are the negative side effects of L-theanine?

No major side effects have been reported, and L-theanine is generally considered safe for most people. Some people may experience side effects like jitteriness, headaches and irritability when drinking too much caffeine from tea.

Everyone is curious about what the future has in store for them. The difference is what we choose to do with that curiosity.

People attempt to find those answers from many sources, like spiritual leaders and palm reading. Sometimes, they even go looking at the bottom of a cup of tea—tasseography is the ancient practice of reading and interpreting the formations of tea leaves at the bottom of the cup.

But you may not need to get to the bottom of your cup to get to the bottom of what’s to come from drinking it. So, what's in that tea? L-theanine, an umami-rich amino acid found in green tea and black tea leaves.

We’ll leave tasseography to the pros and tell you what the future holds in terms of L-theanine’s benefits, dosing variations, and possible side effects.

L-Theanine: The Past and Present

To discuss the future, we have to start with the past. L-theanine’s past is rich, owing to its tea drinker origins. While the first credible documentation of drinking tea is as recent as 300 AD, the first teatime probably occurred in the Yunnan province of China during the Shang Dynasty thousands of years ago. If you believe one popular legend, tea wasn’t discovered on purpose. King Shennong had simply boiled water to make it safe to drink when a gust of wind landed tea leaves from the nearby trees into his drink.Heiss He loved the taste.

King Shennong was also renowned for his willingness to experiment with various herbs and plants to see what effects they would have on him. Lore says his body was translucent so that he could see what was happening on the inside.Heiss For those of us who aren’t lucky enough (or unlucky enough) to see exactly what’s happening, there’s plenty of research surrounding the effects of tea on our bodies.

L-theanine was first isolated from the gyokuro leaf in a laboratory in Kyoto, Japan in . Gyokuro is a type of green tea with a high L-theanine content, though the amino acid can be found in other green, black, and white teas from Camellia sinensis.Scheid

If you want to learn more, please visit our website L-Theanine for Cognitive.

L-theanine is a non-protein and non-dietary amino acid with a chemical structure and blood-brain barrier crossing similar to major neurotransmitters like glutamic acid and gamma-aminobutyric acid (GABA).Yamada Like these neurotransmitters, L-theanine is heavily associated with the effects it can have on our moods.

L-Theanine: The Benefits

From a research standpoint, L-theanine’s future appears bright. This amino acid has a laundry list of health benefits for both the body and brain.

Reduces Anxiety and Stress

If “busy” is a common response you give when someone asks how you’re doing, you may want to add L-theanine to your future for its most acknowledged advantage: the anxiolytic effect. Translation? It may be able to reduce your stress and anxiety symptoms.

In human studies, L-theanine has been linked to anti-anxiety effects possibly through inhibition of cortical neuron excitation.Kimura Unfortunately, excitation of your neurons doesn’t always result in feeling particularly excited. It's more like a stimulant, so you may feel physiological and psychological stresses instead.

Our brains are always balancing this activity through the regulation of different types of neurotransmitters (e.g. dopamine, GABA, serotonin), generally categorized by their excitatory and inhibitory effects. But the system isn’t always perfect. The scales can tip in either direction, which can throw things off balance.

When you have an excess of the excitatory neurotransmitters, you may experience stress and/or anxiety.

You may also accidentally activate your sympathetic nervous system, more commonly referred to as the fight-or-flight response.

While the fight or flight response could save your life in a quick-thinking situation, such as a bear attack, it can be a problem when you activate it without really needing it. At best, it may be a sweaty-palmed nuisance for its acute effects. At worst, you may suffer from chronic stress and its accompanying physiological responses, like an increased heart rate and spike in blood pressure, or an impaired immune system.Glaser

The trigger for physiological stress responses is a release of the stress hormone, cortisol, from your adrenal glands. When L-theanine inhibits excitatory responses in the brain, the body’s regular responses will also be inhibited. Heart rate,Osendarp blood pressure, and even salivary stress markers may all decrease with the help of L-theanine.Kimura

May Help with Sleep

If sleeping is one of the ways you prepare yourself for the future, you may think you need a stronger supplement to help you wind down completely. L-theanine may be the perfect one to tuck you in.

Research shows L-theanine has the ability to generate alpha brain waves, which are typically generated during relaxing activities such as meditation.Juneja When the brain generates alpha waves in the parietal and occipital regions of the brain, you can experience a prolonged calming effect.Kobayashi

Maybe, in your calm and drowsy state, you accidentally poured yourself a late afternoon cup of coffee from the regular pot rather than the decaf. Don’t worry—L-theanine can help ameliorate the effects of the late-night stimulus.Jang Caffeine isn’t just a barrier for your initial drift-off; it’s also a barrier to an adequate amount of slow-wave sleep (SWS), the deepest form of non-REM sleep. In animal studies, L-theanine significantly reversed caffeine’s reductions of slow-wave sleep.Jang

Human studies have yielded promising results as well. A study on L-theanine’s sleep benefits, those with schizophrenia found significant improvements in sleep quality. The results suggest that L-theanine’s therapeutic effect is owed to its stabilization of the glutamatergic concentrations in the brain.Ota Glutamate is a fellow amino acid. But it’s also one of the major excitatory neurotransmitters playing a significant role in schizophrenia.Marsman

In a clinical trial, L-theanine also helped young individuals with attention deficit hyperactivity disorder (ADHD) with their sleep.Lyon Sleep problems are common among individuals with ADHD, and sleep disturbances are equally common in the treatment of the disorder. L-theanine was tested for its safety and efficacy as a sleep aid. The amino acid passed: participants not only fell asleep faster but also experienced higher quality deep sleep after supplementing with L-theanine.Lyon

Can Improve Focus, Memory, and Attention

Maybe sleep isn’t your focus area for improvement; maybe focus is your focus area. If so, surrendering your attention to L-theanine may help it.

Human studies have shown L-theanine can increase focus, reaction times,Haskell and even visual processing, particularly in conjunction with caffeine.Dodd

When supplementing with L-theanine, participants improved attention task performances for well-rounded cognitive function. But the participants didn’t just perform better; they felt better.

"Better" meaning reductions in self-assessed mental fatigue and increases in alertness.Haskell

Let’s not forget what L-theanine can do for your memory. Consuming L-theanine over time gives it a chance to help protect the neurons in your brain from injury and death.Tadeka For those with Alzheimer’s disease, this benefit is huge. In a mouse model studying a pathological mechanism of Alzheimer’s, L-theanine was found to attenuate its cognitive dysfunction through a reduction of associated oxidative damage.Kim

Powerful Antioxidant Properties

We utilize antioxidants to remove an excess of cell-damaging free radicals from our bodies. When our cells and tissues are damaged, it contributes to a host of larger issues and accelerates the arrival of diseases such as heart disease, cancer, and diabetes.

L-theanine’s ability to protect brain cells against oxidative damage contributes to its lengthening certification as an antioxidant. In addition to boosting the production of an infection-fighting antibody,Takagayi L-theanine has been shown to provide direct neuroprotection against neurotoxicants.Cho

L-Theanine: The Side Effects

If you’ve taken sleeping pills before, you know they can get you to bed easily. But getting out of it the next morning? Nearly impossible. The negative side effects of these and other medications may have you making pros and cons lists.

While L-theanine isn’t completely without consequences, your “cons” list won’t be longer than the aforementioned benefits.

Generally Safe

In essence, taking L-theanine is generally considered safe. It hasn’t been linked with any severe adverse effects. But let’s examine the word “adverse” more closely to understand what this description means.

Adverse means “causing harm.” If a medication or supplement “causes harm,” it will be noted. One step further, a “severe adverse” reaction is defined as anything that could be life-threatening, resulting in death, or resulting in a persistent or significant disability.Weiss Think liver failure, serious allergic reactions, and abnormal heart rhythms.

L-theanine has also been tested for its toxicity at extremely high levels.Rao

The results? L-theanine was still tolerated well after two weeks of supplementing with doses nearly sixty times the usual amount used in animal and human studies.

You won’t know the effects of L-theanine until you take it yourself. But numerous clinical trials and research findings have given us a sense of what you should be prepared to experience. The most common side effects of L-theanine dosage include headaches, nausea, and irritability.Giesbrecht However, the nausea appears to be mostly linked with L-theanine being administered through green tea rather than dietary supplements. Similarly, the irritability side effect accompanies the dual administration of caffeine and L-theanine.

No Sedative Side Effects

Even though L-theanine can increase focus and attention, you may be shy to use it because you’re worried its bedtime benefits will kick in during the day.

Luckily, L-theanine is not associated with sedative side effects, despite the stress reduction. L-theanine can generate alpha brain waves associated with relaxation, but these waves will not induce drowsiness.Juneja

May Interact with Other Medications

Because L-theanine doesn’t induce daytime drowsiness in its relaxing effects, you won’t have to worry about it slowing you down. But it may slow your body down without you realizing it.

Remember that L-theanine supplements are able to reduce cortisol levels to inhibit your physiological stress responses. Even if they’re not the target of your L-theanine dose, you should always bear these effects in mind, especially if you’re taking L-theanine in tandem with other medications and supplements.

The dynamic duo: heart rate and blood pressure. L-theanine reduces both, particularly if an individual has high blood pressure.Yoto However, if you’re already on blood pressure medications, be aware that the effects could be either ameliorated or intensified through the introduction of the amino acid.

You should always discuss possible medication and supplement pairings with your healthcare provider before you try them.

L-Theanine: The Dosing

If you are ready to talk to your doctor about adding L-theanine to your daily (or nightly) routine, you’ll want to talk about the appropriate dose.

Safety

Remember that L-theanine is generally considered safe, even in high doses. The extremely high levels were around mg - mg each day. But just because L-theanine didn’t induce toxicity at extremely high levels doesn’t mean you should take exorbitant amounts of this amino acid to achieve the ultimate calm or increase your cognitive performance.

There is no current recommended dosage of L-theanine set by the Food and Drug Administration (FDA). However, clinical trials tend to administer the supplements between 100mg - 250mg.Borzelleca That’s about ten times higher than what you’ll find in a single cup of green tea.Borzelleca Save yourself the future stomach ache of ingesting that much tea and dose accordingly.

Synergy with Caffeine

If you’re looking to get an extra boost from your L-theanine without upping the milligrams, you may want to try pairing it with classic caffeine.

When taken together, the combination of L-theanine and caffeine can have a synergistic effect: increased reaction times,Haskell improvements in acute attention,Kahathudawa and task switching.Eionother Further, because L-theanine is linked to better cerebral blood flow, it can reduce caffeine intake headaches.

The key to their success is proper dosing. If the balance is off, the effects may not be as noticeable. If you’re looking for the improved alertness without the jittery headaches, you should supplement every 150mg caffeine with about 250mg of L-theanine.Haskell

The Future of L-Theanine

Even if you weren’t blessed with the ability to translate the tea leaf traces swirling around your cup, you may be able to exert better control over your own future by supplementing with one of the leaves’ core components.

Contact us to discuss your requirements of L-Theanine for Nootropic. Our experienced sales team can help you identify the options that best suit your needs.