Can L-Theanine Supplements Really Help You Feel Calm and Stay Sharp?

A supplement that promises both relaxation and better concentration sounds appealing. Some brands say L-theanine can deliver exactly that, and dietitians don’t dismiss it outright. There are reasons to think it may help to a certain extent. Still, there is a much cheaper option that often gets overlooked. More on that below.

What Is L-Theanine?

L-theanine is a compound naturally found in tea that is said to support relaxation and focus.

“Have a demanding task at work late in the day but don't want coffee jitters? Tea's combination of caffeine and L-theanine can give you a calm yet alert mental state that could help boost productivity and effectiveness,” says Kate Ingram, MPH, RD, referring to a widely cited study on caffeine and L-theanine published in Cureus. In supplement form, L-theanine is usually sold at around 200 mg per serving. For comparison, a cup of tea generally contains only about 6 milligrams.

What Benefits Are Claimed for L-Theanine?

L-theanine has a rare ability to cross the blood-brain barrier, the semipermeable barrier that shields the brain from toxins and other harmful substances. Not every medication or supplement can pass through it and affect the brain.

Possible cognitive boost

Because it can reach the brain, L-theanine has been marketed as a supplement that may support peak cognitive performance. Some research does point to possible brain-related benefits.

In clinical trials, 100 to 400 milligrams of L-theanine led to a “small but statistically significant” improvement in tasks involving visual attention. When combined with caffeine, people also performed better cognitively than they did without it. The effects may appear after just one dose: People who took a single 200-milligram dose 30 to 60 minutes before a cognitive test scored higher on attention measures.

Possible calmness benefits

Like a good cup of tea, an L-theanine supplement may help ease anxiety and stress. One review suggested that 200 to 400 milligrams could have a calming effect on people who regularly face stressful situations.

Researchers decades ago also proposed that L-theanine users may sleep more soundly and potentially help protect against mental decline. “But the key word is suggest,” says dietitian Perri Halperin, RD. In more recent reviews of claims that L-theanine raises alpha brain waves and improves sleep quality, scientists have found that the findings are often inconsistent.

Immunity claims

One review suggested that L-theanine supplementation could support immune function in livestock. Other studies have found evidence that it may reduce cancer risk as well. But again, those findings were in animals only. No supplement has been proven to boost immunity in people.

What Are the Risks of Taking L-Theanine?

“L-theanine is generally recognized as safe; however, it is always best to consult your healthcare provider before starting any supplement,” says Ingram. That is especially important if you have underlying health conditions or take other medications. L-theanine supplements may interact with some anti-anxiety, blood-pressure, and sleep medications. Side effects can include headaches, dizziness, nausea, and jitteriness.

Do You Really Need It?

As Ingram puts it, “why start a supplement when you can just have a cup of tea?” Tea also comes with other potential health benefits, including support for gut health, weight management, and protection against chronic disease, she says.

The bottom line: a supplement may provide a more consistent dose of L-theanine, but it will cost far more than simply brewing tea. “Tea is certainly a cost-effective way to give it a try,” Ingram says. As always, check with your doctor or a registered dietitian before starting any supplement to make sure it is a good fit for you.

Perri is a New York City-born and -based writer; she holds a bachelor’s in psychology from Columbia University and is also a culinary school graduate of the plant-based Natural Gourmet Institute, which is now the Natural Gourmet Center at the Institute of Culinary Education. Her work has appeared in the New York Post, Men's Journal, Rolling Stone, Oprah Daily, Insider.com, Architectural Digest, Southern Living, and more. She's probably seen Dave Matthews Band in your hometown, and she'll never turn down a bloody mary. Learn more at VeganWhenSober.com.