At Thorne, we’ve noticed an uptick in interest in L-theanine the past year. Is it perhaps due to COVID stress?

This article focuses on how L-theanine can help you deal with stress, as well as having more restful sleep.* But first, what is L-theanine? It’s a non-protein amino acid – meaning it has the structure of an amino acid, but isn’t used as a building block to make proteins. It was discovered in Japan in 1948 as a constituent of green tea, and although it is found primarily in the tea plant (Camellia sinensis), it is present in several other plants, including mushrooms like Boletus badius (bay bolete). L-theanine is synthesized in the roots of plants, but it concentrates in the leaves.

Does all tea contain L-theanine?

Although green tea is its best-known source, L-theanine is found in nearly all teas – black, white, green, and oolong – to one extent or another. The two tables below illustrate the teas that contain the highest and lowest amounts according to a study that assessed the theanine and caffeine content of 36 commercial brands of tea.Another study showed that theanine offsets the stimulatory effect of caffeine – although the ratio of theanine to caffeine dictates to what extent.2 To see all 36 teas, as well as the caffeine and caffeine/theanine ratios, access the full text of the study here.

There are approximately two grams (or 1 tablespoon) of tea per cup. So, if you double the amounts per gram listed below, then that would approximate how much theanine you might get in a cup of tea – an average of 20-25 mg from a cup of tea from the highest-content list.

Teas with the highest L-theanine content1

Commercial tea tested

Type of tea

mg L-theanine per gram of tea leaves

Hwa Gung



Korean Green



ChinaYunnan FOP



Lord Nelson Earl Grey



Vietnamese Green






Mao Feng White



Mao Feng Green




Teas with the lowest L-theanine content1

Commercial tea tested

Type of tea

mg L-theanine per gram of tea leaves

China Yunnan Pu-Erh



Darjeeling Happy Valley



Twinings Earl Grey



Earl Grey



Japanese Bancha



ChinaYunnan White



Russian Samovar



China Gunpowder




What does L-theanine do in the body?

Neurotransmitters: L-theanine can positively impact the key neurotransmitters (brain chemical messengers) involved with stress, sleep, mood, focus, and memory.* L-theanine enhances the production of the neurotransmitters dopamine and serotonin, and also appears to play a role in the formation of GABA – a neurotransmitter that acts like a "brake" during times of stress.* L-theanine helps establish balance in the neurotransmitter system, resulting in improvements in the mental/emotional and physical disturbances resulting from being overly stressed.*

Because serotonin converts to melatonin in the pineal gland in your brain, improving serotonin levels ultimately results in improved melatonin levels, which in turn supports restful sleep.* In one study, 30 healthy adults were given either 200 mg L-theanine or a placebo daily for four weeks. The participants taking theanine took less time to fall asleep, had fewer sleep disturbances, and took fewer sleep medications, compared to the placebo group.3* Those taking L-theanine also had improved mental clarity, measured by verbal fluency, which isn’t hard to imagine – who doesn’t think better after a good night’s sleep?

Brain waves: L-theanine enhances brain alpha-wave activity, a marker of relaxation.* This effect has been observed to be most pronounced in individuals subjectively feeling the highest levels of stress.* 

In one study, healthy participants were given 50 mg L-theanine or a placebo, and brain waves were measured after taking the supplement and 45, 60, 90, and 105 minutes later.Alpha-wave production was significantly higher in the L-theanine group compared to the placebo group. 

Another study of Japanese university students found that 200 mg of L-theanine led to increased brain alpha-waves and a subjective sense of relaxation, along with decreased stress-related beta-waves.*In the same study, L-theanine administration also caused a dose-dependent relaxed, yet alert, state of mind without sedation, beginning approximately 40 minutes after ingestion.* In this study, L-theanine was compared with water and GABA (as PharmaGABA®). Both L-theanine and PharmaGABA significantly increased alpha-wave production compared to water, although alpha-waves were increased more when the subjects took GABA than when they took L-theanine.

In an animal study using brain wave analysis to evaluate sleep, a combination of L-theanine and GABA worked better than either alone in terms of time it took to fall asleep and sleep duration.6*

In general, L-theanine should be considered, along with exercise, a good sleep routine, and stress reduction practices to cope with stress and support restful sleep.*

Check out our new sleep support product – Sleep +. This product packs 200 mg of L-theanine, 100 mg of chamomile, and 1 mg of melatonin into each blueberry-flavored disc. 

Are you interested in knowing your stress or sleep hormone levels? Consider these easy at-home Stress or Sleep tests.


  1. Boros K, Jedlinszki N, Csupor D. Theanine and caffeine content of infusions prepared from commercial tea samples. Pharmacogn Mag 2016;12(45):75-79.
  2. Kakuda T, Nozawa A, Unno T, et al. Inhibiting effects of theanine on caffeine stimulation evaluated by EEG in the rat. Biosci Biotechnol Biochem 2000;64:287-293.
  3. Hidese S, Ogawa S, Ota M, et al. Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial. Nutrients 2019;11(10):2362. 
  4. Nobre A, Rao A, Owen G. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr 2008;17 Suppl 1:167-168. 
  5. Abdou A, Higashiguchi S, Horie K, et al. Relaxation and immunity enhancement effects of gamma-aminobutyric acid (GABA) administration in humans. Biofactors 2006;26(3):201-208. 
  6. Kim S, Jo K, Hong K, et al. GABA and L-theanine mixture decreases sleep latency and improves NREM sleep. Pharm Biol 2019;57(1):65-73.