Sep. 08, 2025
Everyone is curious about what the future has in store for them. The difference is what we choose to do with that curiosity.
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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.
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
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.
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.
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
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
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
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
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.
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.
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.
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Featured content: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
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.
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.
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.
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
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.
If you deal with daily stress or trouble sleeping, you’ve probably turned to a hot cup of tea to settle your nerves. Indeed, there’s good reason tea has a reputation for being so comforting. Research shows that tea can help with everything from lowering cholesterol to improving gut health.
So, it’s natural to think about the ingredients in tea that make it so beneficial. Enter L-theanine — an amino acid that’s present in tea leaves. It’s also used as a supplement, as it may help with anxiety and sleep conditions.
Dietitian Julia Zumpano, RD, LD, talks about what l-theanine is and what you should know before you consider taking it.
L-theanine is an amino acid found in tea leaves, particularly green tea and loose-leaf tea, that has several potential health benefits. But first, let’s go over what amino acids are and why they’re important.
“Amino acids are proteins and they’re really the building blocks of our life,” explains Zumpano. “Amino acids are molecules used by all living things to make proteins. In total, we as humans need 20 different amino acids to function properly. But there are those 11 essential amino acids that our body really needs to get through food.”
While L-theanine isn’t essential for our survival, its presence in plants and fungi has been studied for its possible impact on our brain function.
L-theanine can be taken by drinking certain teas like green teas, white teas or matcha. It can also be taken as a tablet or pill form.
But if you’ve looked up the benefits of L-theanine, you may have started to scratch your head. Some proponents claim it can help you feel more alert, while others say that it can help with insomnia. So, which is it? As Zumpano points out, the best way to get the most use out of L-theanine has a lot to do with when you’re taking it and what you’re pairing it with.
It’s also important to know that these effects may vary from person to person and that there’s still limited research on the benefits of taking L-theanine to help with mental and cognitive issues.
Here are some of the explored benefits of L-theanine:
You may have heard that taking L-theanine before bed can help if you experience disruptive sleep or have trouble falling asleep. A study explored the benefits of an L-theanine and GABA supplement combination on sleep quality and length. GABA, short for gamma-aminobutyric acid, is a naturally occurring chemical messenger in your brain that’s been linked to creating a calming effect. It’s also available as a dietary supplement. The study showed that this combination could potentially increase sleep duration and REM sleep.
According to Zumpano, if you’re looking to try L-theanine in tea or supplement form, it’s a good idea to take it in the evening before going to bed and not pair it with any coffee or caffeinated beverage. If you’re experiencing more serious sleep issues like insomnia or sleep apnea, L-theanine likely won’t do the trick.
Also, you should ask your healthcare provider before pairing any prescription medications with L-theanine before bed. L-theanine can be safely taken with melatonin, however.
Remember how a cup of tea can calm you down after a hectic day? Research shows that L-theanine supplements can elevate your levels of GABA, dopamine and serotonin, which promotes relaxation and reduces anxiety levels.
A randomized trial from found that healthy adults who took L-theanine over the course of four weeks had a decrease in stress-related symptoms. While these results are promising, it’s important to remember that stress reduction will look different for everyone, depending on what stress response you’re having and when you’re experiencing it.
If you’re feeling brain fog or a general blah feeling, L-theanine may be able to help give you a boost of mental clarity and enhance your ability to focus. According to the same study, L-theanine helped healthy adults with verbal fluency and the ability to stay focused. The benefits are heightened when taken with caffeine.
“If you’re going to take L-theanine to gain more alertness and mental clarity, you should take it during the day,” advises Zumpano. “It does seem to do better with coffee or a caffeinated beverage.”
L-theanine is generally considered safe and well-tolerated when taken at appropriate doses. In general, it’s recommended that you don’t exceed 500 milligrams (mg) a day. Most healthy adults can take between 200 mg and 500 mg a day.
But like any supplement, it may cause side effects, particularly at high doses. You can also simply try upping your tea intake to help get a good dose of L-theanine.
“If you’re trying to get your L-theanine in the form of black tea or green tea, then you’re going to have similar side effects like having too much caffeine,” notes Zumpano.
Some of the reported side effects of L-theanine include:
It’s important to add that these L-theanine side effects are relatively uncommon and tend to be mild. L-theanine is generally considered safe for most people, but it’s always a good idea to talk to your healthcare provider before taking any new supplement, especially if you have any underlying health conditions or are taking medications. In addition, if you're pregnant or breastfeeding, you should also exercise caution when taking L-theanine, as there’s limited research on its safety in these populations.
“As of right now, the FDA has classified L-theanine as generally safe, but we don’t have specific guidelines on how to take it, just what the studies have shown,” adds Zumpano.
It’s also important to know that, like all supplements, the U.S. Food and Drug Administration (FDA) doesn’t review or regulate L-theanine products. This means no one checks what’s sold to ensure it’s safe and effective. If you’re planning to try L-theanine in supplement form, you should look for a high-quality version with no added fillers.
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