L-theanine and Heart Palpitations: What Users Say

• lis...
• Taken for less than 1 month
• March 7, 2021

For Dietary Supplementation "I got horrible chest pain and tachycardia (fast heart beats) and palpitations from just 50 mg every time I took it. I haven’t found any warnings of these side effects for this until I came on here. This site is so helpful. Be very careful with this supplement. Start very low and look out for worsening mood and anxiety. I can’t believe no other websites list these common side effects."

• lis...
• Taken for less than 1 month
• March 7, 2021

For Dietary Supplementation "I got horrible chest pain and tachycardia (fast heart beats) and palpitations from just 50 mg every time I took it. I haven’t found any warnings of these side effects for this until I came on here. This site is so helpful. Be very careful with this supplement. Start very low and look out for worsening mood and anxiety. I can’t believe no other websites list these common side effects."

• Dan...
• Taken for 1 to 6 months
• March 26, 2020

For Dietary Supplementation "I have been taking this for about a month, and only now have I started having really weird side effects. At first, it seemed to be greatly helping my anxiety, and for about a week now, I have had awful heart palpitations. I originally thought it was stress but started realizing they would start back up after I took the l-theanine. I was taking 200 mg - 400 mg a day. I also experienced low-grade nausea, especially if I did not eat, as well as dizziness and fatigue. I'm pretty sure I cannot continue this. Also, when I went to the doctor, my blood pressure was very low, and it may have been due to this. I am a 31-year-old female in very good health."

• Res...
• Taken for less than 1 month
• December 26, 2019

For Dietary Supplementation "I took this at night to help with the inability to stay asleep and racing thoughts. I only took it a few times and not every night, more like once or twice a week. I thought it worked well the first night. Then I noticed that when I take it, I have heart palpitations. I have also been having trouble sleeping due to a burning sensation in my stomach. I realized this morning that the burning sensation and heart palpitations only happen when I take this supplement."

• Joe...
• Taken for 1 to 6 months
• August 1, 2019

For Dietary Supplementation "I take 100 mg before bed to help stay asleep through the night. My doc recommended taking it throughout the day as well to increase sleep. It does, but I have had heart palpitations since increasing, especially if I take more than 100 mg in a single dose. So interesting how this supplement interacts with each individual. My body is quite sensitive to anything I take, which accounts for the pounding heart."

• Nes...
• Taken for less than 1 month
• November 2, 2020

For Dietary Supplementation "I started taking l-theanine a month ago. At first, it caused me to have horrible nightmares. I've never had heartburn before, but now I do. I've been in a super weird mood too. Not feeling like myself. I've also noticed random heart palpitations."

• Jjr...
• August 15, 2020

For Dietary Supplementation "My doctor suggested 100 mg 2x daily for general anxiety. I was reluctant in taking my other prescribed anxiety meds (i.e., Xanax), so I figured I’d give this natural alternative a try. I took the Integrative Therapeutics brand because I’d had good experiences with their lavender oil pills (which do work for me, by the way). I took my first pill of 100 mg about 15 minutes after breakfast. By the 45-minute mark, I was beginning to have the worst heart palpitations of my entire life. I thought I was going into convulsions. I tried to eat some bread to absorb the pill, but it began to feel as though my mouth wouldn’t function. I felt like I was losing control of my body. I was beyond irritated and incoherent. Mind you, I’ve suffered from anxiety attacks for the past five years, but nothing like this before. I’m also a 23-year-old, healthy woman. I’m not on any other medications. The extremely high heart rate lasted for close to two hours. This may work for some, but not for me."

• gol...
• Taken for less than 1 month
• November 28, 2021

For Dietary Supplementation "I am a 21-year-old female with medicated ADHD, but no other health problems. Everything I've read has said that L-theanine helps with ADHD stimulant medication jitters, without any side effects. I took 200 mg yesterday afternoon. What followed was what I felt was the worst human experience imaginable. Within 40 minutes, and for 5 hours afterward, I was dissociating for the first time in my life (everything felt distant and like I wasn't in my own body), every muscle was twitching, I was easily startled, tachycardia, I could not stop crying, and every time I closed my eyes, all I could see were rapid flashes of light, as if I was seeing my own neurons firing off. This supplement took me to depths of sadness that I did not know were possible for anyone to feel. Even now, well over 24 hours later, whatever trace amount of L-theanine is still in my system has rendered my ADHD medication useless, and I am still unwell. I hope it clears within the next few days-I just want my life back."

• Tha...
• Taken for less than 1 month
• April 26, 2021

For Dietary Supplementation "I tried supplementing with L-Theanine for stress and noticed that I was getting random heart palpitations. When I stopped supplementing, they went away. It also hides in a lot of supplements. A friend's husband had the same issue from a natural sleep product that had L-Theanine in it."

• Oli...
• Taken for 1 to 6 months
• May 24, 2022

For Dietary Supplementation "I appreciate this does work for some people, and I agree it does relax you... until it wears off! For me, it gave me heart flutters and the worst anxiety ever once it wore off. I just didn't feel like myself and felt like I had a very low mood. Would not recommend, but I appreciate everybody's body chemistry is different. I'll stick to meditation and herbal teas."

• Amw...
• Taken for less than 1 month
• February 25, 2023

"I am grateful to have come across this website review page. It occurred to me, after experiencing lightheadedness, near-fainting spells, and heart palpitations for the past week and a half, that it could be related to something I was taking. I decided to search for information on L-Theanine, as I had added 50 mg of it to my nightly routine about 3.5 weeks ago to aid in sleeping, which it did. I recently visited the doctor to have an EKG and blood work done to investigate these new symptoms, but everything came back normal. However, I did notice a drop in my blood pressure from its usual 120/80 to 90/70, and my heart rate decreased from the 80s to the 70s. Upon reading the reviews, it appears that my recent issues could be linked to L-Theanine. I appreciate everyone sharing their experiences, as everyone is affected differently by various substances. Although some may benefit, others may not. I am currently grateful and have decided not to take L-Theanine tonight."

• Jac...
• Taken for 1 to 6 months
• October 15, 2021

For Dietary Supplementation "Heart palpitations within 5 minutes of taking 100 mg. This is after about one month of usage without any problems. It was providing me the benefit of a clear head, no fogginess when waking up, but the palpitations are concerning and affect sleep quality. Will try to reduce the dosage to 50 mg."

• Jay...
• Taken for less than 1 month
• November 23, 2021

For Dietary Supplementation "Took 225 mg before bed for several nights in a row (4 or 5 maybe). I did sleep well and had vivid dreams. I noticed my premature atrial contractions that I have had diagnosed previously were especially frequent and bothersome. I have had them now and then my whole life, but they are only frequent and dizzying under periods of extreme stress and fatigue, which I am not experiencing right now. I didn't correlate the two until I found others reporting palpitations. Unfortunately, I haven't taken theanine in a couple of weeks, but the problem persists. Obviously, I can't say for sure it caused the problem, but it is the only change in my routine that I can correlate it with. It hasn't gone away with cessation of the supplement, though. 225 mg is quite a high dose apparently. Be careful and start with 50 mg if you are going to try it."

• Mic...
• November 3, 2017

For Dietary Supplementation "I took L-theanine, and it made me a little relaxed, but it gave me heart palpitations. It didn't agree with me. I stopped it."

• Eme...
• Taken for less than 1 month
• November 6, 2021

For Dietary Supplementation "Opened a capsule and took some, and immediately felt anxious, nauseated, and worried with palpitations. Will not try again."

• Dis...
• Taken for less than 1 month
• August 11, 2021

For Dietary Supplementation "Bought l-theanine for sleep aid. Took it an hour ago, and now I'm suddenly having a lot of heart palpitations, which can't be just a coincidence."