L-Theanine Benefits: What It Does and What Studies Show

L-theanine is an amino acid found in tea leaves, and its main benefits in human studies are calm under stress, a relaxed but alert state of mind, better focus when paired with caffeine, and better sleep quality scores. (Kimura et al., 2007; Nobre et al., 2008) A systematic review of 9 controlled trials concluded that 200 to 400 mg a day may help reduce stress in people under stressful conditions (Williams et al., 2020), and in a 4 week trial, 200 mg a day improved sleep quality scores compared with placebo (Hidese et al., 2019). This guide covers what L-theanine does, what each study found, how it feels, and where to go next for dosage, caffeine, sleep and safety.

It is educational, not medical advice.

Key Takeaways

• Calm under pressure: in a double-blind study, L-theanine reduced heart rate and a saliva stress marker during a mental arithmetic stress task compared with placebo (Kimura et al., 2007).
• Relaxed but alert: 50 mg increased alpha brain wave activity, a pattern linked to a relaxed but awake state, in healthy young adults (Nobre et al., 2008).
• Focus with caffeine: 100 mg of L-theanine with 50 mg of caffeine improved speed and accuracy on an attention-switching task and reduced distraction (Owen et al., 2008).
• Sleep quality: 200 mg a day for 4 weeks lowered sleep quality scores (better sleep) and stress-related symptom scores compared with placebo in 30 healthy adults (Hidese et al., 2019).
• Doses studied: 50 mg to 400 mg a day by mouth (Nobre et al., 2008; Williams et al., 2020).

What Is L-Theanine?

L-theanine is an amino acid found in green tea leaves (Kimura et al., 2007). A cup of black tea holds roughly 20 mg (Nobre et al., 2008), which is less than most studies use, so supplements are how people usually reach studied amounts. Our L-theanine ingredient page has more background. Our Saffron Mood and Calm Capsules pair L-theanine with saffron extract in one capsule formula.

L-Theanine Benefits: What the Studies Show

Benefit	Study	Dose	What happened
Calm under stress	12 adults, double-blind, placebo-controlled (Kimura et al., 2007)	Single dose	Lower heart rate and saliva stress marker during a stress task
Less stress overall	Review of 9 controlled trials (Williams et al., 2020)	200 to 400 mg a day	May help reduce stress under stressful conditions
Relaxed, alert mind	Healthy young adults, placebo-controlled (Nobre et al., 2008)	50 mg	More alpha brain wave activity
Focus with caffeine	27 adults, placebo-controlled (Owen et al., 2008)	100 mg with 50 mg caffeine	Faster, more accurate attention switching; less distraction
Sleep quality	30 adults, 4 weeks, double-blind crossover (Hidese et al., 2019)	200 mg a day	Better sleep quality scores, including time to fall asleep
Thinking	Same trial (Hidese et al., 2019)	200 mg a day	Better verbal fluency and executive function scores

1. Calm Under Stress

In a lab study, 12 people did a mental arithmetic task designed to be stressful, with L-theanine, a placebo or nothing, in a double-blind design. With L-theanine, their heart rate and salivary immunoglobulin A (a stress marker) rose less than with placebo, which the authors linked to a calmer response of the nervous system (Kimura et al., 2007). A later systematic review of 9 controlled trials concluded that 200 to 400 mg a day may help reduce stress in people exposed to stressful conditions, and called for longer and larger studies (Williams et al., 2020). Our guide to ashwagandha vs L-theanine compares the two for stress.

2. Relaxed but Alert

L-theanine increases alpha brain wave activity, which the researchers describe as relaxing the mind without inducing drowsiness. Earlier work showed this at higher doses; this study found the effect at 50 mg, in 16 people on L-theanine compared with 19 on placebo, measured over the 105 minutes after taking it (Nobre et al., 2008). That is why it suits daytime use as well as the evening.

3. Focus, Especially With Caffeine

In 27 healthy adults, caffeine alone improved alertness, while 100 mg of L-theanine plus 50 mg of caffeine improved both speed and accuracy on an attention-switching task at 60 minutes and made people less easily distracted in a memory task (Owen et al., 2008). Our guide to L-theanine and caffeine covers ratios and timing, and L-theanine vs L-tyrosine compares two focus amino acids. If you are weighing it against a mushroom, our guide to lion's mane vs L-theanine compares the two for focus.

4. Better Sleep Quality

In a randomized, double-blind crossover trial, 30 healthy adults (9 men and 21 women, average age 48) took 200 mg of L-theanine or placebo daily for 4 weeks. Sleep quality scores improved with L-theanine, including the parts that measure time to fall asleep, sleep disturbance and use of sleep medication, compared with placebo (Hidese et al., 2019). Our guide to L-theanine for sleep covers how much and when.

5. Stress-Related Symptoms and Thinking

In the same trial, stress-related symptom scores fell, and verbal fluency and executive function scores improved, after L-theanine compared with placebo (Hidese et al., 2019). If you are comparing calming options, our guide to GABA vs L-theanine looks at how the two differ for stress and sleep.

How Does L-Theanine Make You Feel?

In studies, L-theanine is linked to a calm, clear state without drowsiness, the relaxed but awake brain wave pattern described above (Nobre et al., 2008). The change is subtle, not sedating. For what studies measured in women, see our guide to L-theanine for women.

How Much L-Theanine and When

Studies used 50 mg to 400 mg a day by mouth (Nobre et al., 2008; Williams et al., 2020). Daytime use suits calm focus, often with coffee or tea; evening use suits sleep. Our L-theanine dosage guide covers amounts and timing, and L-theanine side effects covers safety and how long it lasts. For pairing L-theanine with saffron, see our guide to saffron and L-theanine.

Where Our Products Fit

Our Theanine Nasal Spray provides 36 mg of L-theanine per two-spray serving, is caffeine-free, and can be used as needed; our guide to L-theanine nasal spray explains how to use it. Our Melatonin Nasal Spray pairs 200 mcg of melatonin with 17 mg of L-theanine per serving for bedtime, and the Sleep Stack brings Melatonin Nasal Spray, Theanine Nasal Spray and Lithium Orotate together in one bedtime routine. See our stress, mood and nervous system balance hub for more. Talk to your doctor before starting a new product if you are pregnant, breastfeeding or take medication.

When to Talk to a Doctor

Talk to your doctor or pharmacist before taking L-theanine if you take medication or if you are pregnant or breastfeeding. If stress, worry or poor sleep is affecting your daily life, or you have ongoing anxiety, speak with a doctor or mental health professional rather than relying on a supplement.

Frequently Asked Questions

What is L-theanine good for?

In studies, calm under stress (Kimura et al., 2007), a relaxed but alert state (Nobre et al., 2008), focus when combined with caffeine (Owen et al., 2008), and better sleep quality scores (Hidese et al., 2019).

What does L-theanine do to the brain?

It increases alpha brain wave activity, linked to a relaxed but awake state (Nobre et al., 2008), and it is known to block glutamic acid from binding to glutamate receptors in the brain (Kimura et al., 2007).

How does L-theanine make you feel?

Calm and clear rather than sleepy, according to the brain wave research (Nobre et al., 2008).

Does L-theanine help you sleep?

In a 4 week trial, 200 mg a day improved sleep quality scores, including time to fall asleep, compared with placebo (Hidese et al., 2019).

Can you take L-theanine with coffee?

Yes. 100 mg of L-theanine with 50 mg of caffeine improved attention task performance and reduced distraction compared with placebo (Owen et al., 2008).

What are the benefits of L-theanine for women?

Women were well represented in the research: the 4 week sleep and stress trial enrolled 21 women and 9 men (Hidese et al., 2019).

How much L-theanine should I take?

Studies used 50 mg to 400 mg a day (Nobre et al., 2008; Williams et al., 2020). See our L-theanine dosage guide for timing.

Where does L-theanine come from?

Tea leaves. A cup of black tea holds roughly 20 mg (Nobre et al., 2008).

Sources

1. Kimura K, Ozeki M, Juneja LR, Ohira H. L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 2007. PubMed 16930802
2. Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 2008. PubMed 18296328
3. 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. PubMed 18681988
4. Hidese S, Ogawa S, Ota M, Ishida I, Yasukawa Z, Ozeki M, Kunugi H. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients. 2019. PubMed 31623400
5. 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. PubMed 31758301

Our products are not intended to diagnose, treat, cure or prevent any disease. This article is for education only and is not medical advice.