March 03, 2022 6 min read

You may have seen L-Theanine etched on the side of an energy drink can or bundled in many popular wellness supplements, but you’re still wondering–what is L-Theanine exactly? And why is it heavily marketed as an energy booster?

The truth is, while L-Theanine is a great complement to energy boosting formulas, it’s primary role is to boost concentration and memory. It’s sometimes described as a nootropic, meaning it may boost brain health and increase neurotransmitter activity, but is there any evidence to back up these claims? Let’s take a look:

Table of Contents
About L-Theanine
L-Theanine Benefits and Research
How to Use L-Theanine
L-Theanine Safety
Frequently Asked Questions

Key Takeaways

  • L-theanine is the most common form of theanine, an amino acid that may support general brain health.
  • L-theanine is not essential to the body, but may function similarly to an essential amino acid called glutamate, which is partially responsible for nerve signaling in the brain.
  • Research is limited, but many people believe that L-theanine supplementation can improve cognitive function, concentration, and working memory.
  • If you intend to take L-theanine for its potential brain-boosting benefits, you may consider a multi-functional nootropic blend containing L-theanine and other herbal extracts and brain-boosting vitamins.

About L-Theanine

L-theanine is the most common form of theanine, an amino acid that's not naturally found in the body. However, evidence suggests that theanine can react with the body similarly to glutamate, a naturally occurring amino acid that helps send nerve signals in the brain.

A cup of green tea is rich in L-theanine and a supporting caffeine content

You can find theanine in some foods and beverages, like many different types of tea leaves and mushrooms. Although theanine is not considered essential to the human body, some evidence suggests that it may help improve concentration, hence why you may see it added to energy drink blends or other wellness supplements designed to support energy and focus.

Theanine may also affect other important brain chemicals, like GABA, dopamine, and serotonin, although it's unclear if this poses a benefit to all consumers. You'll frequently find people who use L-theanine to manage stress and poor sleep, improve cognitive function, or reduce anxiety, although evidence is still inconclusive for many of these uses.

Although L-theanine is popularly used on its own to help improve memory and cognitive functions, it might be most effective when used alongside caffeine and other brain stimulating supplements. Before we get too tied up in the hearsay, though, let's look at the research available to support the benefits of L-theanine:

L-Theanine Benefits and Research

L-theanine research is currently limited, but some there are some areas of interest, including the following:

Improved Focus

A 2012 study suggests that tea, specifically black and green varieties, may help improve focus. In this study, subjects took 100 mg of L-theanine combined with 50 mg of naturally occurring caffeine. Participants who drank the tea generally made fewer errors in attention-demanding tasks than the participants taking the placebo.

Improving Sleep

A 2018 study found that participants reported better sleep quality after taking doses of up to 900 mg of L-theanine daily for up to 8 weeks. Many of these participants suffered from anxiety or depression and were taking prescription antidepressants. The general consensus is that L-theanine may help increase relaxation to help people sleep more easily, but more research is needed to fully understand L-theanine’s sleep-enhancing potential.


An extensive 2016 review supports these results. L-Theanine in black and green tea was found to potentially improve relaxation by lowering a person’s resting heart rate.

Increasing efficacy of some cancer treatments

The same 2016 study also found that L-theanine in tea may also enhance the effectiveness of doxorubicin, a chemotherapy drug. The research found that L-theanine-containing beverages may increase the amount of the drug that enters cancer cells.

Increased cognitive performance

Again, the same review found that the L-theanine compound may be useful for improving brain function and providing neuroprotective benefits. The research suggests that L-theanine could improve focus, reaction times, and alertness. It’s important to note that in this research L-theanine was combined with the naturally occurring caffeine in either black or green tea.

Boosting the immune system

That 2016 review also supports the idea that L-theanine may boost immune functions. In general, it may increase the body’s potential to fight off disease and lessen the chance of a person catching common illnesses like the cold or the flu.

Reducing blood pressure

Evidence is limited, but research that has found L-theanine to reduce heart rate and lower stress may also indicate that it has the ability to reduce blood pressure.

Read "L-Theanine Benefits" to learn more.

How to Use L-Theanine

It’s important to note that supplements are not regulated in the same way as medications are in the U.S., so it’s important that you carefully consider the quality of the L-theanine supplements you choose. Also pay close attention to dosing, since the dosage for L-theanine isn’t standardized.

Here are some things to consider when designing your L-theanine dosing routine:

Source and Quality Importance

The quality of your wellness supplements is incredibly important, especially since supplements are not regulated the same way as prescription medications. Ensure that the L-Theanine supplement you buy comes from a trustworthy manufacturer, specifically that uses a third-party testing process to ensure quality. You may also look for a company that is experienced with wellness supplements and uses a cGMP compliant manufacturing facility.

When Should I Take L-Theanine?

If you're hoping to take L-theanine to improve concentration, it's best to take it first thing in the morning with your coffee or approximately 30 minutes before breakfast. You may need to take L-theanine daily for a week or more before you experience the full benefits.

Some people choose to take L-theanine to support a healthy sleep routine. In this case you may take your nighttime dose about 30 minutes before bed. All In all, the most important thing is that you take L-theanine around the same time every day in order to get the best results.

How Much L-Theanine Should I Take Daily?

A standard dose of L-tyrosine starts at 100 milligrams (mg) daily. However, L-theanine has most often been used in doses of 200-400 mg daily for between 4 and 8 weeks. For daily use, however, doses between 100 mg and 250 mg are most often used.

Because L-theanine is not regulated like prescription drugs are in the US, there are no standardized dosing suggestions. You may want to start at the low end of this dosing threshold and wait a few weeks to see the effects before deciding to increase your dose.

It's important to talk to your doctor before using L-theanine, especially if you take prescription medications or suffer from a serious or chronic condition.

Read "L-Theanine Dosage" to learn more. 

A person holding an L-theanine capsule, one dosing form that is convenient for daily use

Forms of L-theanine

L-theanine and D-theanine are the two forms of the amino acid theanine, although L-theanine is much more common. You'll generally find it in capsule form, but it can also be found as a powder that can be added to foods or beverages. Certain food sources, like green tea, have bountiful amounts of L-theanine, too. While L-theanine capsules are convenient, many people prefer to take L-theanine with other nootropic and adaptogenic herbs and supplements designed to support brain health and general wellness. For this reason, L-theanine is popular in powder form, specifically when used as part of a multifunctional formula.

L-Theanine Safety

The FDA has classified L-theanine as GRAS, or “generally recognized as safe,” meaning they believe L-theanine products to be safe when used according to package directions. Some people should not take L-theanine without first talking to their doctor, including people who are pregnant or breastfeeding or those who take the following substances:

  • Drugs for high blood pressure
  • Any drugs that may lower blood pressure
  • Prescription stimulants, like medications for ADHD
  • Stimulant street drugs
  • Supplements that contain large amounts of caffeine

In general, it’s always best to talk to your doctor before adding a new supplement to your wellness routine.

Read "L-Theanine Side Effects" to learn more. 

Frequently Asked Questions

What does taking L-theanine do?

L-theanine is an amino acid found in many types of tea and some functional mushrooms that’s found in supplement form in the U.S. Preliminary evidence and anecdotal reports suggest that it may help to manage anxiety and stress, reduce insomnia, and improve concentration. As with all supplements, you should talk to your doctor before adding L-theanine to your wellness routine.

What are the side effects of L-theanine?

There are no officially reported side effects for L-theanine, but it often is combined with caffeine that can cause nausea, mood disruptions, or upset stomach in large doses.

Is L-theanine the same as caffeine?

No, but the two are often bundled together. On its own, L-theanine is not a stimulant like caffeine, but the two are thought to function together to help increase focus.

Should I take L-theanine every day?

There is currently no official L-theanine dosage guideline in the United States because L-theanine is classified as a supplement. Some studies have found that doses of up to 400mg per day are considered to be safe and well tolerated by most people.


  1. “Assessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention task”
  2. “L-theanine in the adjunctive treatment of generalized anxiety disorder: A double-blind, randomised, placebo-controlled trial”
  3. “L-Theanine as a Functional Food Additive: Its Role in Disease Prevention and Health Promotion”
  4. “GRN No. 209: L-theanine”

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