Last updated: October 2026
L-theanine is an amino acid found mainly in tea. Small trials suggest 200 to 400mg a day may help people feel less stressed in stressful situations, and that combined with caffeine it can sharpen focus on demanding tasks. A 2019 trial also found better sleep scores. Evidence is promising but limited, and L-theanine has no authorised health claims.
Below: what L-theanine is, what the research shows for stress, focus and sleep, how much is in tea, dose, safety, and where we use it.
What is L-theanine?
L-theanine is an amino acid that occurs naturally in tea leaves, especially green and black tea, and in some mushrooms. It isn’t one of the amino acids your body needs from food. It’s thought to influence brain chemicals linked with relaxation and attention, which is why it’s often paired with caffeine in “calm focus” products, and used in evening blends.
What the research shows
| Use | Study | What it found |
|---|---|---|
| Stress | Systematic review, 2020 | 200 to 400mg a day may help reduce stress and anxiety in people under stressful conditions; trials were small |
| Stress and sleep | 4-week trial, 2019 (30 adults, 200mg a day) | Improved stress-related symptoms and sleep quality scores compared with placebo |
| Focus, with caffeine | Trials, 2008 | Caffeine plus L-theanine improved accuracy on demanding tasks more than caffeine alone |
L-theanine isn’t a treatment for anxiety or insomnia. See natural supplements for anxiety and natural sleep aids ranked by evidence.
How much is in tea?
A cup of tea contains a small amount of L-theanine, usually well under the 200mg used in trials, along with caffeine. Matcha and some green teas contain more. So tea can be part of a calm routine, but you’d need a supplement to reach trial doses. See caffeine and anxiety.
Dose and timing
- Typical trial doses: 100 to 400mg a day.
- For focus: trials paired about 100mg with a moderate amount of caffeine, earlier in the day.
- For winding down: in the evening, often in a blend with magnesium.
- How long: some effects were seen after a single dose; the sleep trial ran for 4 weeks.
Safety
- Generally well tolerated in trials at up to 400mg a day; occasional headache or stomach upset.
- Blood pressure medicines and sedatives: check with a pharmacist, as L-theanine may add to their effects.
- Pregnancy and breastfeeding: not enough safety data; we don’t recommend our products during pregnancy or breastfeeding.
Where we use L-theanine
Our Magnesium Glycinate Sleep Complex combines magnesium bisglycinate and citrate (148mg of magnesium per serving) with glycine, L-theanine and botanicals, as a warm evening drink. Magnesium contributes to normal psychological function and the reduction of tiredness and fatigue. See magnesium for sleep and what’s in a magnesium complex.
FAQs
What does L-theanine do?
Small trials suggest it may help people feel less stressed and, with caffeine, focus better on demanding tasks. Evidence is limited.
Does L-theanine help you sleep?
One 4-week trial of 200mg a day found better sleep quality scores. It isn’t a sleeping tablet.
How much L-theanine should I take?
Trials used 100 to 400mg a day. Follow the product label and check with a pharmacist if you take medicines.
Can I take L-theanine with coffee?
Yes, many people do. Trials found caffeine plus L-theanine improved focus on demanding tasks more than caffeine alone.
Is L-theanine safe to take every day?
It was well tolerated in trials at up to 400mg a day. Long-term data is limited.
Sources
- Williams JL 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.
- Hidese S et al. Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults. Nutrients, 2019.
- Owen GN et al. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci, 2008.
- Haskell CF et al. The effects of L-theanine, caffeine and their combination on cognition and mood. Biol Psychol, 2008.
