Ingredients · 6 min read
L-theanine and caffeine: what the research shows
What the trials tested, what they found, and whether there’s an ideal ratio.
By the Romeé teamUpdated 4 sources
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The quick version
- L-theanine is an amino acid found naturally in tea leaves. Shade-grown tea, like matcha, has more of it.
- In randomized trials, caffeine plus L-theanine improved attention and alertness on lab tests within an hour or two.
- A 2014 review of 11 trials found improvements in alertness and attention switching for the pair.
- Every Romeé flavor contains green tea extract, a source of L-theanine.
The short answer
In controlled studies, people given caffeine plus L-theanine did better on tests of attention than people given a placebo. A 2014 review that pooled 11 randomized trials found improvements in alertness and attention switching within two hours.[1]
Three studies are worth knowing.
What is L-theanine?
L-theanine is an amino acid found naturally in tea leaves. Tea plants grown in shade, like those used for matcha, build up more of it, along with more caffeine.[2] One analysis cited in a 2020 review found as much as 44.65 mg of L-theanine per gram of matcha.[2]
What the studies found
Owen and colleagues, 2008
Twenty-seven healthy adults took 50 mg of caffeine, the same caffeine with 100 mg of L-theanine, or a placebo, on separate days. An hour later, the combination improved both speed and accuracy on an attention-switching task. It also made people less susceptible to distracting information during a memory task, at 60 and 90 minutes.[3]
Haskell and colleagues, 2008
This double-blind trial compared 250 mg of L-theanine, 150 mg of caffeine, and the two together. The combination improved reaction times, working memory speed and accuracy on several tasks. People also rated themselves less tired, more alert, and lower on headache.[4]
Camfield and colleagues, 2014
This systematic review and meta-analysis pooled 11 randomized controlled trials of tea compounds. Caffeine and L-theanine together improved alertness and attention switching within two hours.[1]
Is there an ideal L-theanine to caffeine ratio?
Not an established one. Owen’s study used 2 parts L-theanine to 1 part caffeine. Haskell’s used 250 mg to 150 mg, closer to 1.7 to 1. Both found benefits with the combination.[3, 4]
L-theanine in Romeé
| Flavor | L-theanine source on the label | Caffeine |
|---|---|---|
| Matcha Focus | Green tea extract, plus matcha | 85 mg |
| Strawberry Hydrate | Green tea extract | 100 mg |
| Citrus Recharge | Green tea extract | 125 mg |
| Berry Energy | Green tea extract | 150 mg |
What this means for you
If you’re curious about the pairing, start with a caffeine dose that suits you, and keep your total within the guidance in our caffeine guide. If you’re weighing matcha against coffee, we compared the two in matcha vs coffee.
From Romeé
Every Romeé flavor contains L-theanine from green tea extract. The caffeine is printed on every can.
Pre-order now. Orders ship once our first production run is in hand, ahead of our Fall 2026 launch.
Frequently asked questions
What does L-theanine do with caffeine?
In controlled trials, people given caffeine plus L-theanine did better on attention tasks, like switching between tasks, than people given a placebo. A 2014 review of 11 trials found improvements in alertness and attention.
What is the best L-theanine to caffeine ratio?
There isn’t an established one. The trials we cite used roughly 1.7 to 2 parts L-theanine per part caffeine, and both found benefits with the combination.
Does matcha have L-theanine?
Yes. Matcha comes from tea plants grown in shade, which raises the leaf’s L-theanine and caffeine. One analysis cited in a 2020 review found up to 44.65 mg of L-theanine per gram of matcha.
Which Romeé flavors contain L-theanine?
All four. Each one contains green tea extract, a source of L-theanine.
Is L-theanine natural?
Yes. L-theanine is an amino acid found naturally in tea leaves, and shade-grown teas like matcha contain more of it.
Sources
- 1.Camfield DA, Stough C, Farrimond J, Scholey AB. Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis. Nutrition Reviews. 2014;72(8):507-522. Review
- 2.Kochman J, Jakubczyk K, Antoniewicz J, Mruk H, Janda K. Health Benefits and Chemical Composition of Matcha Green Tea: A Review. Molecules. 2020;26(1):85. Review
- 3.Owen GN, Parnell H, De Bruin EA, Rycroft JA. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutritional Neuroscience. 2008;11(4):193-198. Study
- 4.Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB. The effects of L-theanine, caffeine and their combination on cognition and mood. Biological Psychology. 2008;77(2):113-122. Study
This article is for general education. It is not medical advice. If you are pregnant, nursing, under 18, sensitive to caffeine, or managing a health condition, talk to your doctor.