July 18, 2023/Wellness

Here’s What You Need To Know About L-Theanine

Timing and pairing are important to reap the possible benefits of this amino acid

A cup of frothy green tea in foreground and powdered matcha in background.

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.


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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.

What is L-theanine?

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.

Benefits of L-theanine

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:

Improving sleep quality

You may have heard that taking L-theanine before bed can help if you experience disruptive sleep or have trouble falling asleep. A 2019 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.

Reducing stress and anxiety

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 2019 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.

Boosting mental clarity

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 2019 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.”


Side effects and risks

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:

  • Headaches.
  • Dizziness.
  • Nausea.
  • Jitteriness.
  • Irritability.
  • Diarrhea.

Is it safe?

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, pregnant or breastfeeding (chestfeeding) people 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.

Learn more about our editorial process.

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Amino Acids

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