L-theanine is a natural amino acid found almost exclusively in green tea leaves (Camellia sinensis). It is known for producing a relaxing effect without causing drowsiness.
What is L-theanine?
It is a non-protein amino acid: it is not part of the body's proteins, but it crosses the blood-brain barrier and acts directly on the brain. It is responsible for the "calm alertness" sensation from green tea. As a supplement, it is usually taken alone or together with caffeine.
How does it work?
- Calm without sedation: it increases alpha brain wave activity, which is associated with a state of relaxation while the mind is alert.
- Modulates neurotransmitters: it promotes the activity of GABA, serotonin, and dopamine, and balances the action of glutamate.
- Stress response: it has been associated with lower physiological reactivity to stress, such as heart rate and cortisol.
What does science say?
Stress
A systematic review concluded that 200 to 400 mg of L-theanine per day can reduce stress and anxiety in people exposed to stressful situations (Williams 2020).
Sleep
In a trial with healthy adults, 200 mg per day for four weeks improved stress-related symptoms and sleep quality (Hidese 2019). It is not a sedative: it facilitates pre-sleep relaxation without causing next-day drowsiness.
Concentration and mental performance
In the same Hidese study, improvements were observed in some cognitive functions, such as verbal fluency. Combined with caffeine, L-theanine improves attention and reduces errors in demanding tasks (Owen 2008).
Anxiety
In a trial on people with generalized anxiety, L-theanine as an adjunct to treatment showed no differences compared to placebo regarding anxiety, although it did improve sleep satisfaction (Sarris 2019). Its role in this area requires further study.
Dosage and how to take it
- The studied doses range from 100 to 400 mg per day; 200 mg is the most common.
- For rest, it is usually taken 30 to 60 minutes before sleep.
- For concentration, it can be taken in the morning, alone or with coffee or tea.
- It can be taken with or without food.
Safety
- It has an excellent safety profile and is well tolerated at the studied doses.
- There is insufficient data regarding pregnancy and breastfeeding, so it is recommended to consult a doctor first.
- If you take blood pressure medication or treatments for anxiety or sleep, consult a healthcare professional.
Frequently asked questions
Does L-theanine make you sleepy?
No. It relaxes without sedating, which is why it can be taken during the day. At night, it helps you unwind before sleep.
Can it be taken with coffee?
Yes. It is one of the most studied combinations: L-theanine softens the jitters from caffeine, and together they improve focus.
How long does it take to take effect?
The relaxing effect is noticeable between 30 and 60 minutes after taking it. The effects on stress and sleep have been evaluated after about four weeks of daily use.
References
- 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.
- Williams JL, Everett JM, D'Cunha NM, et al. The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: a systematic review. Plant Foods Hum Nutr. 2020;75(1):12-23.
- Owen GN, Parnell H, De Bruin EA, Rycroft JA. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci. 2008;11(4):193-198.
- Sarris J, Byrne GJ, Cribb L, et al. L-theanine in the adjunctive treatment of generalized anxiety disorder: a double-blind, randomised, placebo-controlled trial. J Psychiatr Res. 2019;110:31-37.
L-theanine promotes sustained attention, mental focus, and working memory.
L-theanine promotes sleep onset and improves sleep quality.
L-theanine lowers cortisol levels and reduces stress
