Skip to main content

L-Theanine: What Is It, Benefits, Risks, and Side Effects

5 min read

By Chris Brown

Medically Reviewed by Julie Ching, MS, RDN, CDE

L-theanine isn’t exactly a household name just yet, but it sure seems like more and more people are asking about it every day. It’s easy to understand why. A quick glance at the list of its potential benefits is enough to intrigue even the most skeptical among us.

What exactly is L-theanine? Is it safe? Today, we’re going to present as many answers as the scientific community can provide and hopefully give you yet another thing to talk about while hanging around your gym’s water cooler.

What Is L-Theanine?

You may already be an active consumer of L-theanine and not even know it yet. As a naturally occurring compound in black and green teas, trace amounts of L-theanine can likely be found in most of our bloodstreams. Tea is the second most consumed beverage in the world after all.

It’s an amino acid that was discovered as a component of green tea way back in 1949 and has been consumed safely ever since. L-theanine has since been extracted and is popularly supplemented in pill or tablet form.

Benefit: Stress Relief

Many around the world reach for a warm cup of tea to close out a long and stressful day and the scientific data may explain why. L-theanine has been shown to be capable of relaxing the mind without causing drowsiness. This study concluded that 200 to 400-milligrams (mg) of L-theanine per day can assist in reducing anxiety and acute stress in people experiencing stressful situations.

Much more research needs to be done on the stress-relieving benefits of regular L-theanine consumption but the data that we do have is no doubt encouraging.

Benefit: Focus

We could all use a mental boost when taking on a particularly challenging cognitive task. Might we suggest 97-mg of L-theanine and 40-mg of caffeine?

One study was able to establish a concrete link between that supplementary cocktail and significantly improved task accuracy and self-reported alertness. Something to consider next time you find yourself running to the vending machine.

Benefit: Cognitive Performance

More than just focus, L-theanine may contribute to improved cognitive performance in those who consume it regularly.

Based on some of the findings thus far, L-theanine could improve a person’s reaction time, alertness, and learning ability. However, some studies are claiming the contrary too, which is why the scientific community at large is urging for more research.

Benefit: Better Sleep

Mixing in a little L-theanine into your nightly sleep routine may do more than help you de-stress and unwind. L-theanine supplementation played a big role in decreasing sleep latency and improving NREM sleep in this study.

In another study, participants described enjoying greater sleep satisfaction after 8-weeks of daily L-theanine supplementation. If you struggle with sleep every night you might want to consider L-theanine.

Benefit: Lower Blood Pressure

High blood pressure, and the laundry list of health complications that derive from it, is an endemic problem for much of the modern world. All the more reason to be particularly excited about the research surrounding this truly wondrous amino acid.

The stress-reducing effect of consuming L-theanine may also decrease an individual’s blood pressure over time. After all, reducing your stress is often recommended to those with high blood pressure.

Benefit: Weight Loss

Foodies may be familiar with the term Umami, but let’s briefly break it down for those of you out there that don’t subscribe to the FOOD network. Umami is basically another word for savoriness and is considered one of the five basic tastes alongside saltiness, sweetness, bitterness, and sourness. You experience it a lot when eating cooked meats and broths.

Apart from being delicious, umami flavoring has been linked to increased feelings of fullness and a reduction in appetite. This is where L-theanine comes in. L-theanine is largely responsible for the umami flavor of green tea. Though research is limited, the theory posits that L-theanine consumption may make you feel fuller longer, and in turn suppress your appetite.

Benefit: Improved Immune System

There’s something to be said for L-theanine’s ability to help the body fight off colds and flu. What limited evidence we do have points to a few incredible benefits that supplementation can have on the function of the immune system.

The research also touts L-theanine’s anti-inflammatory properties, which may play a role in fighting off illness too.

Benefit: Strengthens Cancer Treatment

Nobody is telling you to self-diagnose or self-prescribe medications. That’s your doctor’s job. All we’re here to do is shine a light on the early-stage potential of L-theanine supplementation.

Doxorubicin is a popular chemotherapy drug, and some limited animal research has displayed increased effectiveness when administered in tandem with L-theanine. Not all chemotherapy drugs have positive effects of using L-theanine so do not use this without discussing it with your oncologist first.

Side Effects

Currently, there are no known side effects to L-theanine consumption or supplementation. It’s currently classified as generally recognized as safe by the Federal Food and Drug Administration (FDA), and that doesn’t look like it’s about to change anytime soon either.

Through the consumption of tea, L-theanine has been leaned on safely by human civilization for centuries and it looks like there’s no need to stop now.

Risks

As far as risks are concerned, there are a few things to note. Though consuming L-theanine through tea is perfectly safe, it’s important to recognize the reality of purchasing supplements. The dietary supplement industry is largely unregulated, which is something to keep in mind whenever you purchase supplements.

If you are currently relying on other forms of medications as prescribed by your doctor, it may be best to consult them before supplementing with L-theanine. L-theanine may interact with your current prescription in unforeseen ways, so it’s always safer to seek advice from a medical professional.

The Takeaway

It really is incredible how much we still have to learn about the things that we consume every day. L-theanine has been a dietary staple for much of modern civilization, for almost as long as it’s existed. And, the more you read about it, the easier it is to understand why.

Whether supplemented or consumed through tea, L-theanine shows a lot of potential. It may boost your immune system, enhance cognitive performance, improve the quality of your sleep, and even help chemotherapy treatments, all with little to no side effects. But as always, consult with your doctor before taking a new supplement.

MS, RDN, CDCES

Julie Ching is a Registered Dietitian and Certified Diabetes Educator in Los Angeles. She decided to become a Dietitian after traveling through Europe, South America, and Asia and discovered a passion for food. She now works with people of all ages and varying disease states to improve their health. She is passionate about teaching people about nutrition so they can live their best life while still considering their cultural and socioeconomic backgrounds.

Diet and Nutrition News & Advice

Explore

Dietary Fibre Affects More Than Your Colon: How the Immune System, Brain and Overall Health Benefit Too
By Mark Wulczynski Diet and Nutrition News & Advice

Dietary Fibre Affects More Than Your Colon: How the Immune System, Brain and Overall Health Benefit Too

There’s no shortage of advice about what to eat, including hype about the latest superfoods that will help you live to 100, or about the newest restrictive diets that claim to help you lose weight and look beautiful. As a researcher from the Farncombe Family Digestive Health Research Institute, I’m well aware that there is […]

Read More about Dietary Fibre Affects More Than Your Colon: How the Immune System, Brain and Overall Health Benefit Too

4 min read

What’s the Best Diet for Healthy Sleep? A Nutritional Epidemiologist Explains What Food Choices Will Help You Get More Restful Z’s
By Erica Jansen Diet and Nutrition News & Advice

What’s the Best Diet for Healthy Sleep? A Nutritional Epidemiologist Explains What Food Choices Will Help You Get More Restful Z’s

You probably already know that how you eat before bed affects your sleep. Maybe you’ve found yourself still lying awake at 2 a.m. after enjoying a cup of coffee with dessert. But did you know that your eating choices throughout the day may also affect your sleep at night? In fact, more and more evidence […]

Read More about What’s the Best Diet for Healthy Sleep? A Nutritional Epidemiologist Explains What Food Choices Will Help You Get More Restful Z’s

5 min read

Does an Apple a Day Really Keep the Doctor Away? A Nutritionist Explains the Science Behind ‘Functional’ Foods
By Janet Colson Diet and Nutrition News & Advice

Does an Apple a Day Really Keep the Doctor Away? A Nutritionist Explains the Science Behind ‘Functional’ Foods

We’ve all heard that an apple a day keeps the doctor away, but how true is that? Apples are not high in vitamin A, nor are they beneficial for vision like carrots. They are not a great source of vitamin C and therefore don’t fight off colds as oranges do. However, apples contain various bioactive […]

Read More about Does an Apple a Day Really Keep the Doctor Away? A Nutritionist Explains the Science Behind ‘Functional’ Foods

6 min read