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Who wouldn't want to take a pill and quickly experience less stress and anxiety without unpleasant side effects? It comes as no surprise then that when people on social media started claiming L-theanine could do just that, it grew in popularity.
However, as with most wellness trends, the benefits of taking L-theanine aren't quite that straightforward. While it's true that L-theanine is a good-for-you plant compound, no single food or supplement will ever catapult us to a "perfect" state of health or "fix" all of our ailments.
“We do know that the effects of L-theanine are very specific to the person taking it. L-theanine may have antioxidant benefits, in terms of reducing inflammatory markers, may have anti-cancer properties and appears to reduce inflammation specifically in the gut microbiome,” explains Janese Laster, M.D., a board-certified gastroenterologist in Washington, DC.
Of course, may is the key word. L-theanine may do wonders for one person and not the next. And, as with any supplement, no one should take it without getting the green light from their doctor or dietitian first. If you're considering including L-theanine in your daily routine, here's everything you need to know about it so you can have an educated conversation with your healthcare professional.
What is L-theanine?
L-theanine is an amino acid, a.k.a. a molecule that helps build protein in the body. It’s known for being found in green tea, but it's also in other herbal brews such as white, black and oolong teas.
Recently, L-theanine has become popular in supplement form, but that's not always the best way to ingest it. "The reality is, if you take a supplement, the amount of L-theanine in it can vary. You can’t know for sure how much you’re getting,” says Dr. Laster.
A doctor or dietitian can also help you choose a quality supplement brand; in general, your best bet is to look for recognized third-party testing certifications that can verify the quality of what you’re buying (NSF and USP, for example, ensure that a supplement contains what it says it does and that it doesn’t have unacceptable levels of impurities).
What are the benefits of L-theanine?
L-theanine could boost your health in a number of ways. “Research suggests that L-theanine may help support stress management, sleep and potentially weight management,” says Colleen Tewksbury, Ph.D., R.D., L.D.N., a national spokesperson for the American Academy of Nutrition and Dietetics and assistant professor of nutrition science at the University of Pennsylvania School of Nursing in Philadelphia.
Studies also suggest that L-theanine may support liver and kidney function, heart health, digestion and immunity. One small study reported that L-theanine may have a positive effect on cognitive function, attention and memory, while another small study discovered that L-theanine may impact specific brain receptors that promote feelings of calm and relaxation. Of course, there's no guarantee that every person will experience any or all of these benefits.
When is the best time to take L-theanine?
Any time is fine, but it's a good idea to see how it makes you feel before settling on a regular supplement-popping time. For instance, if L-theanine produces a relaxing vibe for you, taking it before bed might be a smart move. “Evening may be best, due to the supplement making some people feel drowsy,” says Tewksbury. Can L-theanine really help you sleep? The latest research suggests it could, but there's nothing definitive, as many studies have not used "pure" samples, or they've been focused on animals or a small number of people.
L-theanine also has the potential to sharpen your attention span and other cognitive capabilities, so taking it in the morning or during the day might work better for you if these are the effects you feel. Fortunately, L-theanine is one of those supplements that you should be able to take on an empty stomach without a big risk of feeling queasy — but always check the supplement label and instructions, just in case!
Are there side effects or risks to taking L-theanine?
Again, supplements affect everyone differently, but, “common side effects may include headache, nausea and drowsiness” for some people, says Tewksbury.
You shouldn't take L-theanine supplements if:
- You are pregnant or breastfeeding
- You're allergic to green tea
- You take sedatives, antidepressants, blood pressure medication, anti-seizure drugs or asthma medication
The bottom line:
While L-theanine may have the potential to enhance your life and benefit your health in certain areas, “always discuss your individual potential risks and benefits of starting a supplement with your primary care provider,” Tewksbury stresses. “If you decide to start taking this supplement, be sure to disclose it along with all of your medications on future healthcare visits.” L-theanine might indeed give your health a nice boost – but you always want to play it safe.
Stefani (she/her) is a registered dietitian, a NASM-certified personal trainer and the director of the Good Housekeeping Institute Nutrition and Fitness Lab, where she oversees all nutrition and fitness-related content, testing and evaluation. She holds a master’s degree in clinical nutrition from New York University, as well as advanced certifications as a Women's Fitness Specialist and a Behavior Change Specialist. Stefani is dedicated to providing readers with evidence-based content to encourage informed food choices and healthy living. She is an avid CrossFitter and a passionate home cook who loves spending time with her big fit Greek family.
