Animal study: L-theanine, caffeine and sleep

Are you unable to get to sleep because there’s too much caffeine [structural formula below left] racing round your body? Then you might benefit from L-theanine [structural formula below right]. Researchers at Kyungpook National University in South Korea write about this in Pharmacology, Biochemistry and Behavior. The Koreans did experiments on rats and discovered that L-theanine supplementation partially negated the negative effects of caffeine on sleep.


L-Theanine is an amino acid that is found in small quantities in tea. Green tea contains more L-theanine than black tea, but white tea contains more L-theanine than green tea does. One cup of tea contains about 25-40 mg L-theanine.

In the brain L-theanine interacts with glutamate receptors in a complex way, as a result of which L-theanine has both a sedative and stimulatory effect. Studies have shown that L-theanine reinforces the stimulatory effect of caffeine on some mental processes and also enhances mood. [Biol Psychol. 2008 Feb;77(2):113-22.] [Nutr Neurosci. 2008 Aug;11(4):193-8.] [Appetite. 2010 Apr;54(2):406-9.] [Nutr Neurosci. 2010 Dec;13(6):283-90.] [J Nutr. 2008 Aug;138(8):1572S-1577S.]

Most human studies on the effect of stretching used untrained students as the test subjects. But do men and women with years of weight training experience react in the same way? To answer this question the Brazilians performed a small study using 9 untrained [UT] and 11 trained [RT] males in their twenties. The trained men had been doing weight training for six months.

The Koreans were curious to know what effect L-theanine would have on one of the less positive effects of caffeine. Caffeine keeps people from sleeping. So would L-theanine enhance that effect too? Or would the amino acid actually weaken this effect?

To find out the researchers did experiments with rats. The Koreans gave the lab animals injections directly into their small intestine containing water with no active ingredients [Cont], 7.5 mg caffeine per kg bodyeight [CT10], or with caffeine and 22.5 [CT1], 37.5 [CT2], 75 [CT3] or 150 [CT4] mg L-theanine per kg bodyweight. This form of administration imitates the effect of oral administration.

The researchers then studied the effect of the injections on the rats’ sleep.

The administration of caffeine extended the amount of time that the rats were awake during their sleeping period [W]. L-Theanine did not reduce the amount of time. L-Theanine did have an influence on the structure of the sleep of the rats. The figure below shows that L-theanine partially obliterated the negative effect of caffeine on the duration of slow wave sleep [SWS].

Slow wave sleep is the phase in which the body secretes hormones like growth hormone and in which it carries out repair processes. It’s an extremely relevant sleep phase for athletes.


L-Theanine had no influence on the amount of time the rats needed to reach slow wave sleep [tSWS] or REM sleep [REMS].

It is during REM sleep that we dream. It’s thought that the brain deletes superfluous information during REM sleep and stores relevant information neatly.

The human equivalent of the lowest – and most effective – dose that the researchers used was about 200-400 mg L-theanine. Higher doses had the opposite effect. Whether lower doses work even better the Koreans have not researched, but they suspect that this is the case.

The researchers suspect that L-theanine not only improves quality of sleep in people who ingest large amounts of caffeine, but also in people who have sleep problems. They warn of the danger of using too high doses, because this is what came out of their own animal study.

Most supplements manufacturers advise users who want to improve their sleep quality to take 100 mg L-theanine. And while we’re on the subject of supplements manufacturers: and they didn’t pay this study. The researchers were funded by the South Korean government.

L-theanine partially counteracts caffeine-induced sleep disturbances in rats.


L-theanine has been reported to inhibit the excitatory effects of caffeine. The present study examined the effects of L-theanine on caffeine-induced sleep disturbances in rats. Rats received the following drug pairings: saline and saline (Control), 7.5 mg/kg caffeine and saline, or 7.5 mg/kg of caffeine followed by various doses of L-theanine (22.5, 37.5, 75, or 150 mg/kg). Vigilance states were divided into: wakefulness (W), transition to slow-wave sleep (tSWS), slow-wave sleep (SWS), and rapid-eye-movement sleep (REMS). Caffeine significantly increased the duration of W and decreased the duration of SWS and REMS compared to the Control. Although L-theanine failed to reverse the caffeine-induced W increase, at 22.5 and 37.5 mg/kg (but not at 75 and 150 mg/kg), it significantly reversed caffeine-induced decreases in SWS. In conclusion, low doses of L-theanine can partially reverse caffeine-induced reductions in SWS; however, effects of L-theanine on caffeine-induced insomnia do not appear to increase dose-dependently.

PMID: 22285321 [PubMed – indexed for MEDLINE]