What is L-Theanine

But first, what is L-theanine? 

IL-theanine is a nonprotein 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 plants and fungi, including the bay bolete (Boletus badius) mushroon. Although L-theanine is synthesized in the roots of plants, 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.¹ 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 2 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 of L-theanine from a cup of tea from the highest-content list.

Teas with the highest L-theanine content¹

Teas with the lowest L-theanine content¹

What are L-theanine benefits?

What is L-theanine good for? L-theanine can provide several benefits for a stressed out human body. Several clinical trials demonstrate L-theanine’s positive impact on key neurotransmitters (brain chemical messengers) involved with stress, sleep, mood, focus, and memory. 

Support for mental focus. In one study, researchers found that taking L-theanine supported participants’ mental focus. Participants who took a 100-mg L-theanine dosage made fewer errors in an attention task than those in the placebo group.³

Another study found 200 mg L-theanine given to a group of college students with a propensity to become stressed resulted in improved attention and reaction time during visual and auditory test situations.⁴ It did not have the same benefit in the group of college students who did not have a tendency to be stressed.

Relaxation/stress support. L-theanine benefits include enhancing the production of the neurotransmitters dopamine and serotonin, and it 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.

In addition to modulating neurotransmitters, 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 45, 60, 90, and 105 minutes after taking the supplement.⁵ 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 an increase in brain alpha-waves and a subjective sense of relaxation, along with decreased stress-related beta-waves.⁶ 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. Both L-theanine and GABA 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.

Support for quality sleep. Does L-theanine help sleep? Several studies indicate L-theanine might improve sleep quality. As was mentioned above, L-theanine enhances serotonin production, which converts to melatonin in the pineal gland in your brain, which in turn supports restful sleep. 

In one study, 30 healthy adults were given either a 200-mg L-theanine dosage 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.⁷ 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?

In further research, an animal study using brain wave analysis to evaluate sleep, determined that a combination of L-theanine and GABA worked better than either alone in terms of time it took to fall asleep and sleep duration.⁸ 

If you’re looking for help with sleeping, L-theanine may be a useful option. 

L-Theanine Side Effects and Safety

Amounts of L-theanine of 900 mg daily have been used safely, although most adults consume smaller doses of 200-400 mg daily. L-theanine has a very low side effect profile – the most common being drowsiness or a headache.