Available as a supplement and in some foods, L-theanine is an amino acid that may have some health benefits.
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Reviewed by Dietitian Jessica Ball, M.S., RDReviewed by Dietitian Jessica Ball, M.S., RD
L-theanine is a nutrient found in some plants and supplements. It has gained popularity for its potential health benefits, particularly related to stress relief and improved sleep. We spoke with registered dietitians to get the full scoop on L-theanine, from benefits and side effects, to who should take it and who should avoid it.
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L-theanine is a non-protein, water-soluble amino acid known for its potential to promote relaxation and ease stress without causing drowsiness. It is found naturally in plants like matcha, green, black and white teas, and fungi like some mushrooms. It is also available in supplement form, typically as a pill or powder.
While L-theanine is best known for helping people relax, it may have other potential health benefits as well.
According to Kelsey Costa, registered dietitian nutritionist and founder of Dietitian Insights, “L-theanine may have significant therapeutic effects on mental health, such as reduced depression and stress and improved emotional and cognitive function.”
Studies show that L-theanine helps lower stress-related symptoms, improve sleep quality and promote cognitive function in both healthy individuals and those with major depressive disorders. Athletes and other individuals under stress have also reported improved performance and reduced stress responses when using L-theanine.
L-theanine may enhance attention, focus and cognitive performance. It may be even more effective when combined with caffeine, which can help improve memory and executive function, and reduce distractions and mind wandering. L-theanine might also be beneficial for people with ADHD because it supports sustained attention and impulse control. However, more research on this topic is needed to clarify the relationship, especially for kids and young adults.
L-theanine has antioxidant, immunoregulatory and anti-inflammatory properties. Studies suggest it may decrease the instances of respiratory infections, aid in flu prevention and decrease inflammation in the digestive tract.
“It's important to note that many of the available studies on potential health benefits have small sample sizes, show limited improvements and often involve healthy individuals rather than those with chronic health problems,” says Emily Haddock, RD, LDN, registered dietitian and owner of Music City Nutrition & Wellness. Additional research is needed on more diverse populations to further clarify and support these benefits.
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“With the small bit of research currently available, there aren't many confirmed side effects or direct risks associated with taking L-theanine,” Gabbie Ricky, M.S., RDN, performance nutrition specialist, tells EatingWell.
“As with any supplements you're considering, however, make sure you purchase from a reputable manufacturer. Look for supplements that have the Good Manufacturing Practices (GMP) certification and have been rigorously third-party tested for product quality and purity,” she adds.
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Some side effects associated with L-theanine are often due to the overconsumption of caffeine by those who increase L-theanine intake by drinking tea. These side effects may include:
Headaches
Nausea
Jitteriness
Irritability.
The recommended daily intake of caffeine is 400 milligrams or less.
“People who regularly work in high-risk environments or under high levels of stress may benefit from the potential cognitive benefits of L-theanine, such as improved focus especially when paired with caffeine,” says Ricky. “Some examples of these populations might include professional athletes, tactical athletes (like firefighters, military personnel, etc.) and healthcare workers,” she adds.
People with poor sleep quality, depression and anxiety might also benefit from L-theanine, but it's important to talk with a healthcare provider before adding any new supplements to your routine.
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While L-theanine is safe for most people, some should avoid it. “People who are pregnant or lactating should avoid L-theanine as it has not been adequately tested in these populations,” adds Haddock.
People who take medications for high blood pressure may need to avoid L-theanine, as it may further reduce blood pressure.
Also, anyone receiving chemotherapy for cancer treatment should avoid L-theanine supplements until after their treatment course is complete. “In supplemental doses, the potent antioxidant function of L-theanine may reduce the efficacy of certain chemotherapy drugs,” Ricky tells EatingWell.
It’s always recommended to speak with a healthcare provider before adding any new supplements to your routine, particularly if you are undergoing treatment for cancer or high blood pressure.
L-theanine is a non-protein amino acid that is found in some foods like tea and mushrooms. It is also available in supplement form. Many people may be able to safely take L-theanine without negative side effects, but some people (like those who are pregnant or undergoing cancer treatment) should avoid it. While L-theanine shows promise of potential health benefits, more extensive research is needed on larger and more diverse populations to confirm this.
Is it safe to take L-theanine every day?
Based on current information available, most healthy adults can take L-theanine daily without negative health consequences or side effects. Generally, it's safe to drink tea and take supplements containing L-theanine every day. However, talk to your doctor before starting to make sure it’s safe for you.
Does L-theanine make you sleepy?
L-theanine may improve sleep quality by reducing stress and promoting a sense of calm. It isn’t usually associated with sleepiness or drowsiness during the day, but may contribute to better sleep at night.
What are the negative side effects of L-theanine?
No major side effects have been reported, and L-theanine is generally considered safe for most people. Some people may experience side effects like jitteriness, headaches and irritability when drinking too much caffeine from tea.
I’ve been using Nutraharmony L-Theanine for a couple of weeks, and I’m very pleased with the results. It helps me feel more relaxed and less overwhelmed by daily stressors. I’ve also noticed an improvement in my ability to stay focused during long meetings. The capsules are easy to swallow, and there’s no aftertaste, which is a plus. My only minor complaint is that it took a few days to start noticing the effects, but once it kicked in, it worked great.
I started taking l-theanine to aid in weight loss. I had read that it can reduce stress and cortisol (stress hormone) levels which would aid in appetite control and help with weight loss. It makes me feel fuller longer and makes me uncomfortably bloated if I overeat. It's not exactly how I thought it would help lol but it's effective nonetheless. It's helping me realize when I'm just wanting to eat out of boredom or habit and I know if I do it'll be uncomfortable so it really stops me in my tracks. I... don't see the product I use on the list. It's Nature Made chewable 200mg. Read More Read Less
Menopause caused my sleep to become disrupted. I have spent years trying everything to get 8 hours of sleep a night. I can go to sleep initially very easily but I wake up around 2:30 to use the bathroom and then am unable to get back to sleep. I started taking a supplement that contains several types of magnesium and L-theanine. It is a powder you mix with water. What works for me is to sip half of the water before I go to sleep and then drink the rest after I get up to use the bathroom in the... middle of the night. I will usually read a couple of pages from a book while I wait for the powder to start working. I fall back asleep within 15 or 20 minutes and feel refreshed when I wake up in the morning. I love this stuff. Read More Read Less
Note: I haven't been on this supplement for too long and have took it in the evening, always. First time I took it in the early evening, I did feel the positive effects after about an hour such as relaxation, slight euphoria, but after having slight trouble going to sleep that night I woke up at 5 AM wide awake out of nowhere (probably after a dream which I had no recall of). Falling asleep past that point was a massive struggle. Today, I took another 100mg, got a little sleepy after 1 hour but... once again, can't fall asleep. This time it's worse, as it's been >2 hours after intake and I still can't fall asleep + have a pretty bad headache. For now, I've noticed it's done everything other than what was advertised in my case. I have not been on my the entire time until now, and even if I was, without Theanine I'm pretty sure I'd be asleep by now. Does this mean your experience will be the same? No. A lot of people find this substance helpful but please be careful taking it. Start from the lowest dose and see how you react. Read More Read Less
I discovered L-Theanine by investigating on line what could help with anxiety. I bought some and started taking it daily not really expecting it to do much. Well, I can honestly say that it is the best thing I have ever taken. It rid me of all my anxiety within a few days and I felt great. I took it for months and then thought that I would give myself a break from it. I was fine for a couple of months and then I could feel the anxiety rearing its ugly head again so I started back on the L-Theanine... and, within a couple of days, I could feel the effects again. I love it!! Read More Read Less
I have moderate health anxiety and occasional panic attacks. I never wanted to take prescription medicine for it, out of the fear of it making me feel not like myself. I researched heavily the pros and cons of L-theanine before I was brave enough to try it! And seriously wow, I don’t know why physicians don’t suggest this to more patients with anxiety. It gives me such a sense of calm throughout the day, I can feel the anxiety build in overwhelming situations but then level out on the days I’ve taken... it. I take 100mg everyday with my coffee and it has changed my life for the better! Also I was not prompted to write this review, I just want to help anyone whose going through the same thing and looking for something to level them out Read More Read Less
Reviews about weird vivid dreams are correct. I use it nightly with Ashwagandha and sleep great. During the day I can't take it due to sleepiness. NOTE: Combining with 5-HTP made my head feel like it was on fire- like severe HEAT from the vitamins metabolizing. I had to run my head under cold water. L-Theanine helps vitamins cross into brain cells by making the cell walls open up for absorbing vitamins. So, it you're used to the average 10% of your vitamins soaking into your brain you will... find that now your urine will no longer be yellow from vitamins unabsorbed. Those vitamins are now in your brain and if not careful you might find yourself zoning out or confused. I had a few hours one day where I had no idea where I was or even what day it was. Moral to the story: great vitamin supplement, but just take 1/2 dose for the first day, skip a day, and then resume 1/2 dose until going 100% dose in a couple of days. I have found using every other day gives me the same or better benefit, and costs less :) Read More Read Less
L-theanine has been a complete life-changer (in a good way), and this is coming from someone who almost always notices no effect from any medication or supplement! It “smooths out” daytime anxiety but most importantly for me—I can sleep at night now without waking constantly due to to highly anxious thoughts. I am writing this on vacation at 5 a.m. because I ran out of l-theanine and I’ve woken up every hour due to work anxiety. When I first started taking it, my dreams were wild but that lasted... less than a week and now I don’t have stressful work dreams anymore (like I had every night before taking l-theanine). For me, it works amazingly well. Read More Read Less
Was Getting 4-5 hours of sleep a night due to perimenopause. Nothing seemed to work/ I started to feel like a walking medicine cabinet with the only options left being highly addictive Rx sleeping pills. Meditation didn't ablate the isse either. My MD and I nearly pulled the trigger on Seroquel, used for insomnia off-label ( but can lead to hyperlipodemia and blood sugar issues) when I stumbled upon L-theonine (and 5-HTP) at the health food store. For the first time in YEARS(!!!) I am sleeping... like a baby and getting an easy 8 hours per night. Would highly recommend! Amazing! Read More Read Less
I don’t remember how I discovered it but I’m so glad I did I’ve tried everything to sleep I was waking up four times a night my Fitbit was revealing that my blood oxygen level was spiking and my heart rate was above normal resting quite a bit of the night. I did some research. I have been taking Xanax since I was 19 years old I’m now 64 and I don’t take it much anymore because I don’t like it. I was looking for something to help me sleep when I stumbled across this. I started taking 200 mg and it... really helped me to sleep and relax right away. I’m now taking 100 mg about an hour before bed and boy does it relax you. It definitely has helped me I feel more clear when I wake up not like I slept eight hours and feel like I didn’t get any sleep it’s definitely helping me so far and I pray to God it continues to because I needed some thing and I don’t like to take drugs. I hope this helps others. I also suffer from depression and it definitely helps my state of mind as well. Read More Read Less
While this product is with out a doubt relaxing, it is not for sleep. I found that using it nightly (200mg) after 5 days it actually made my sleep much worse in all regards: getting to sleep, waking up multiple times and waking early. When I stopped my old sleep patterns returned. While my doctor recommended this on my next office visit he did say it can reduce serotonin which can cause sleep issues. Anyway, I give it high marks on relaxation, bad on insomnia.
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