Type your caffeine and your L-theanine. You see the ratio, whether it and each amount sit inside what the twelve human trials of the pair actually gave, the trial nearest to your amounts with what it found — and the trials where the pair did nothing extra. It never tells you how much to take.
Your ratio
2.1 to 1, L-theanine to caffeine 200 mg of L-theanine with 95 mg of caffeine
Inside the ratios the 12 trials gave (0.67 to 1 up to 2.4 to 1).
200 mg of L-theanine is inside what the trials gave (50 to 250 mg); 95 mg of caffeine is inside what the trials gave (40 to 250 mg).
The trial nearest to your amounts: Haskell et al. 2008 — 250 mg of L-theanine with 150 mg of caffeine (1.7 to 1). Haskell et al. 2008: “the combination also led to faster simple reaction time, faster numeric working memory reaction time and improved sentence verification accuracy”
Of the 12 trials, 8 found the pair better than placebo on at least one attention measure, 3 found no benefit of the pair beyond its parts or beyond placebo, and 1 measured blood pressure and mood instead.
| Trial | L-theanine | Caffeine | Ratio | What it found |
|---|---|---|---|---|
| Dodd et al. 2015 | 50 mg | 75 mg | 0.67 to 1 | the theanine cancelled caffeine’s effects; no gain in behaviour |
| Rogers et al. 2008 | 200 mg | 250 mg | 0.8 to 1 | theanine blunted caffeine’s blood-pressure rise; alertness and jitteriness unchanged |
| Giles et al. 2017 | 200 mg | 200 mg | 1 to 1 | the pair did not differ from placebo |
| Kahathuduwa et al. 2017 | 200 mg | 160 mg | 1.3 to 1 | recognition reaction time improved; effects additive at high doses |
| Kahathuduwa et al. 2018 | 200 mg | 160 mg | 1.3 to 1 | faster responses to targets than placebo |
| Nawarathna et al. 2025 | 200 mg | 160 mg | 1.3 to 1 | better hit rate than placebo after a night without sleep |
| Haskell et al. 2008 | 250 mg | 150 mg | 1.7 to 1 | the pair beat placebo on several attention and memory-speed measures |
| Kelly et al. 2008 | 100 mg | 50 mg | 2 to 1 | the pair beat placebo on an attention task |
| Owen et al. 2008 | 100 mg | 50 mg | 2 to 1 | the pair improved attention switching at 60 minutes |
| Foxe et al. 2012 | 100 mg | 50 mg | 2 to 1 | no added benefit over caffeine or theanine alone |
| Einöther et al. 2010 | 97 mg | 40 mg | 2.4 to 1 | better on a switching task; alertness not improved |
| Giesbrecht et al. 2010 | 97 mg | 40 mg | 2.4 to 1 | better task-switching accuracy and alertness than placebo |
This is not medical advice and it never suggests a dose: it places your amounts among published trials. The FDA’s 400 mg of caffeine a day is a line for healthy adults, not a target; in pregnancy, with a heart condition, or with blood thinners, antidepressants or blood-pressure medication, ask your doctor or pharmacist.
The “2 to 1” people quote is 100 mg of L-theanine with 50 mg of caffeine — the dose in three of the twelve trials. The others ran from 0.67 to 1 (50 mg with 75 mg) up to 2.4 to 1 (97 mg with 40 mg), and three of the twelve found the pair did nothing extra. No trial here gave more than 250 mg of either at once. The twelve are the human trials that gave the two together in one dose and stated both amounts.
How to use it
Type your caffeine in milligrams, or pick a coffee and the page takes USDA’s figure for that cup. Type the L-theanine on your capsule’s label. You see your ratio (L-theanine to caffeine), whether it and each amount sit inside what the twelve trials gave, and the trial nearest to your amounts with the sentence its authors wrote about what they found. The table lists all twelve, lowest ratio first. The page never works out a dose for you: there is no official one, and scaling a small trial’s ratio up to your coffee would be inventing one.
What the trials gave, and what they found
Each row below is from that trial’s own PubMed abstract. The two smallest caffeine doses: “compared a combination of L-theanine (97 mg) and caffeine (40 mg) to a placebo on two attention tasks” (Einöther and colleagues, 2010) and “a combination of 97 mg L-theanine and 40 mg caffeine as compared to placebo treatment” in 44 young adults (Giesbrecht and colleagues, 2010). The 2 to 1 trials used “placebo, 100 mg of L-theanine, 50 mg of caffeine, or these treatments combined” (Kelly, 2008), set out “to compare 50 mg caffeine, with and without 100 mg L-theanine, on cognition and mood in healthy volunteers” (Owen, 2008), or “were administered caffeine (50 mg), theanine (100 mg), the combination, or placebo” (Foxe, 2012). The largest: “L-theanine (250 mg), and caffeine (150 mg), in isolation and in combination” (Haskell, 2008), 200 mg with 160 mg in three trials that share an author, and “250-mg caffeine, 200-mg theanine, both or neither of these” (Rogers, 2008).
| Trial | L-theanine + caffeine | Ratio | In the authors’ words |
|---|---|---|---|
| Dodd et al. 2015 | 50 mg + 75 mg | 0.67 to 1 | “However, at the levels tested here, this did not lead to a positive impact on behaviour.” |
| Rogers et al. 2008 | 200 mg + 250 mg | 0.8 to 1 | “Theanine antagonised the effect of caffeine on blood pressure but did not significantly affect jitteriness, alertness or other aspects of mood.” |
| Giles et al. 2017 | 200 mg + 200 mg | 1 to 1 | “when consumed together, they counteract the effects of each other” |
| Kahathuduwa et al. 2017 | 200 mg + 160 mg | 1.3 to 1 | “Theanine and caffeine seem to have additive effects on attention in high doses.” |
| Kahathuduwa et al. 2018 | 200 mg + 160 mg | 1.3 to 1 | “l-Theanine and l-theanine-caffeine combination resulted in faster responses to targets compared with placebo” |
| Nawarathna et al. 2025 | 200 mg + 160 mg | 1.3 to 1 | “The L-theanine-caffeine combination significantly improved the hit rate (P = 0·02) and target-distractor discriminability (P = 0·047), compared with the placebo.” |
| Haskell et al. 2008 | 250 mg + 150 mg | 1.7 to 1 | “the combination also led to faster simple reaction time, faster numeric working memory reaction time and improved sentence verification accuracy” |
| Kelly et al. 2008 | 100 mg + 50 mg | 2 to 1 | “We found an increase in hit rate and target discriminability (d’) for the combined treatment relative to placebo” |
| Owen et al. 2008 | 100 mg + 50 mg | 2 to 1 | “The L-theanine and caffeine combination improved both speed and accuracy of performance of the attention-switching task at 60 min” |
| Foxe et al. 2012 | 100 mg + 50 mg | 2 to 1 | “The combined treatment did not confer any additional benefits over either compound alone” |
| Einöther et al. 2010 | 97 mg + 40 mg | 2.4 to 1 | “significantly improved attention on a switch task as compared to the placebo, while subjective alertness and intersensory attention were not improved significantly” |
| Giesbrecht et al. 2010 | 97 mg + 40 mg | 2.4 to 1 | “significantly improved accuracy during task switching and self-reported alertness (both P < 0.01) and reduced self-reported tiredness (P < 0.05)” |
Counted plainly: 8 of the 12 found the pair better than placebo on at least one attention measure, 3 found no benefit of the pair beyond its parts or beyond placebo, and 1 measured blood pressure and mood instead. The three that found nothing extra are worth reading whole. Dodd and colleagues, at tea strength: “Combining L-theanine with caffeine, at levels and ratios equivalent to one to two cups of tea, eliminated the vasoconstrictive effect and behavioural effects of caffeine.” Giles and colleagues, at 200 mg of each: “Thus, under emotional arousal, caffeine and theanine exert opposite effects on certain attentional processes, but when consumed together, they counteract the effects of each other.” So the same blunting that people take the pair for can also take away what the caffeine was doing.
What the reviews conclude
Two meta-analyses have pooled these and similar trials. Camfield and colleagues (2014): “Evidence of moderate effect sizes in favor of combined caffeine and L-theanine in the first 2 hours postdose were found for outcome measures Bond-Lader alertness, attentional switching accuracy, and, to a lesser extent, some unisensory and multisensory attentional outcomes.” — and, on which of the two does the work, “Moderator analysis of caffeine and L-theanine doses revealed trends toward greater change in effect size for caffeine dose than for L-theanine dose, particularly during the first hour postdose.” Payne and colleagues (2025), with fifty trials: “small-to-moderate differences were found between these interventions in the first hour (h1) and second hour (h2), that favoured theanine plus caffeine”, but “The CIs frequently highlighted the uncertainty surrounding the direction and magnitude of these differences.” Their conclusion is a careful one: “This meta-analysis provides evidence that theanine plus caffeine, and theanine alone, could be beneficial for cognitive and mood outcomes.”
On L-theanine by itself, a 2026 mini-review of the systematic reviews says “supplementation with 100-400mg of L-theanine can produce small but statistically significant improvements in aspects of cognitive performance, particularly on visual attention tasks and when combined with caffeine”, that “Supplementation with L-theanine has generally been reported to be well-tolerated in clinical trials.”, and that “Further high-quality studies are warranted to establish optimal dosing strategies, clarify underlying mechanisms and evaluate potential interactions with other bioactive compounds.” L-theanine has no Daily Value and no official upper limit to measure a label against; caffeine does have a line — the FDA: “For most adults, the FDA has cited 400 milligrams a day — that’s about two to three 12-fluid-ounce cups of coffee — as an amount not generally associated with negative effects.”
Worked examples
- An 8 fl oz coffee (95 mg) with a 200 mg capsule (the page’s example): 2.1 to 1, inside the ratios the trials gave. The nearest trial is Haskell 2008’s 250 mg with 150 mg.
- A 100 mg capsule with half a cup’s caffeine (50 mg): exactly 2 to 1 — the three 100 mg + 50 mg trials, one of which found no added benefit.
- 100 mg of L-theanine with 300 mg of caffeine: 0.33 to 1 — less L-theanine per milligram of caffeine than any trial gave, and more caffeine than any gave at once.
- A 400 mg capsule with a single espresso’s 63 mg: 6.3 to 1 — more L-theanine than any of these trials gave at once.
Common mistakes
- Treating 2 to 1 as a rule. It is one pair of doses (100 mg + 50 mg) in three small trials. Kahathuduwa’s 2017 trial describes its 200 mg as “A dose of theanine equivalent of eight cups of back tea” — the ratios in these trials were chosen by the researchers, not found to be best.
- Scaling the ratio up to a big coffee. A 16 fl oz coffee is about 189 mg of caffeine; “2 to 1” on that is 378 mg of L-theanine, more than any of these twelve trials gave at once.
- Expecting it to add focus on top of caffeine. Three trials found the pair no better than its parts or than placebo, and Camfield’s meta-analysis found trends toward the effect following the caffeine dose more than the L-theanine dose.
- Counting only the capsule’s caffeine. The FDA’s 400 mg is for the whole day; the Caffeine Content Chart adds up everything else you drink.
Frequently asked questions
What is the best ratio of L-theanine to caffeine?
No trial compared ratios against each other, so none is “best”. The trials gave from 0.67 to 1 up to 2.4 to 1; the often-quoted 2 to 1 is the 100 mg + 50 mg used in three of them.
How much L-theanine should I take with coffee?
There is no official amount. The trials of the pair gave 50 to 250 mg of L-theanine with 40 to 250 mg of caffeine. Type your coffee and your capsule above to see the nearest trial and what it found; your own amount is a question for your doctor or pharmacist.
What is the usual L-theanine dosage in studies?
In the twelve combination trials, 50 to 250 mg at once. A 2026 review of L-theanine alone describes 100 to 400 mg in healthy adults.
Does L-theanine with caffeine actually work?
Sometimes, modestly. 8 of the 12 trials found the pair better than placebo on at least one attention measure; 3 found no benefit beyond the parts or beyond placebo. The 2025 meta-analysis says the differences favoured the pair but that the confidence intervals “frequently highlighted the uncertainty”.
Does L-theanine cancel out caffeine?
In two trials it did: at tea strength (50 mg with 75 mg) it “eliminated the vasoconstrictive effect and behavioural effects of caffeine”, and at 200 mg of each the two “counteract the effects of each other”. In Rogers’s trial it blunted caffeine’s rise in blood pressure without changing alertness.
How much L-theanine is in tea or matcha?
Far less than a capsule per cup of tea — one trial calls 200 mg “equivalent of eight cups” of black tea. Matcha has more; the Matcha vs Coffee tool shows the L-theanine measured in 143 matchas.
Read next
- L-Theanine Nootropic Review
- Caffeine as a Nootropic – Benefits, Dose, Side Effects and More
- Can You Take Mind Lab Pro With Coffee?
- 7 Supplements for Motivation and Energy
This is not medical advice, and nothing here diagnoses or treats anything. It places two amounts among published trials; whether the pair suits you is a conversation with your doctor or pharmacist — especially with blood thinners, antidepressants or blood-pressure medication. Some links on this site are affiliate links: I buy what I review at full price, and a commission never changes a verdict.