MitoGenix Guides
L-Theanine and Caffeine: What the Research Shows
If you're searching for L-theanine and caffeine in South Africa, you've probably seen the same claim repeated: the two work better together than caffeine alone. Some trials support that. Others don't. This guide walks through what was actually tested, at what doses, and where the results disagree, so you can judge it for yourself.
Why these two are studied together
Both occur naturally in tea. Caffeine is the stimulant. L-theanine is an amino acid found almost only in tea leaves. Researchers noticed that tea feels different from coffee and began testing the two compounds separately and together, usually in single-dose trials with tasks such as attention switching, reaction time and vigilance.
What the trials found
Most of this research is acute, meaning a single dose followed by tests within about 30 to 90 minutes. Here is what the main human trials reported:
| Study | Dose | Participants | What it reported |
|---|---|---|---|
| Owen et al., 2008 [1] | 100 mg L-theanine + 50 mg caffeine | 27 healthy volunteers | Combination improved speed and accuracy of attention switching at 60 minutes and reduced susceptibility to distraction. |
| Haskell et al., 2008 [2] | 250 mg L-theanine + 150 mg caffeine | Healthy adults, double-blind crossover | Combination improved several measures including vigilance accuracy and reaction times. L-theanine alone increased "headache" ratings and lowered one arithmetic score. |
| Giesbrecht et al., 2010 [3] | 97 mg L-theanine + 40 mg caffeine | 44 young adults | Better task-switching accuracy and alertness, less self-reported tiredness. No effect on visual search, choice reaction time or mental rotation. |
| Rogers et al., 2008 [4] | 200 mg L-theanine + 250 mg caffeine | 48 healthy adults | L-theanine reduced caffeine's rise in blood pressure but did not significantly change jitteriness or alertness. |
| Dodd et al., 2015 [5] | 50 mg L-theanine + 75 mg caffeine | 24 adults | Combination removed caffeine's effects on blood flow, attention and mood. No positive behavioural effect at these doses. |
What the reviews say
- 2014 meta-analysis (11 trials). It found moderate effects in favour of the combination on alertness and attention-switching accuracy in the first two hours after a dose. The size of the effect appeared to follow the caffeine dose more than the L-theanine dose [6].
- 2025 meta-analysis (50 trials reviewed, 15 pooled). Small to moderate differences favoured L-theanine plus caffeine on attention-switching accuracy and digit vigilance accuracy in the second hour. The authors note the confidence intervals often highlighted uncertainty about the size and direction of effects, and that more research in free-living people is needed [7].
Where the results disagree
An honest summary has to include the trials that didn't line up:
- At low doses, Dodd and colleagues found the combination cancelled caffeine's effects instead of adding to them [5].
- Rogers and colleagues found L-theanine lowered caffeine's blood-pressure effect but did not change how alert or jittery people felt [4].
- Haskell and colleagues saw L-theanine alone increase headache ratings, even though the combination performed better on several tests [2].
The studies also used different doses, different tests and small samples. That's why reviews describe the evidence as promising but not conclusive.
And L-theanine on its own?
- A 2025 meta-analysis of 5 trials in 148 healthy adults found effects on some tests (rapid visual information processing and visual reaction time) but not others (simple reaction time and the Stroop test). The authors concluded the benefit could not be confirmed on every test method [8].
- A 2026 meta-analysis of 31 randomised trials (1,168 participants) found a single 200 mg dose taken 30 to 60 minutes before testing improved choice reaction time. Effects on stress were modest and mostly from studies at higher risk of bias. No serious adverse events were reported [9].
How the doses compare with Mito-Focus Xtreme
| Source | L-theanine | Caffeine | Ratio |
|---|---|---|---|
| Owen 2008 | 100 mg | 50 mg | 2 : 1 |
| Giesbrecht 2010 | 97 mg | 40 mg | about 2.4 : 1 |
| Haskell 2008 | 250 mg | 150 mg | about 1.7 : 1 |
| Mito-Focus Xtreme (2 capsules) | 200 mg | 100 mg | 2 : 1 |
The label sits inside the range used in these trials. It is not a claim that the finished stack was tested as a whole. Mito-Focus Xtreme also contains Alpha-GPC, L-Tyrosine and Huperzine A, and the research above covers only the L-theanine and caffeine pair.
How to use it sensibly
- Count your caffeine. Mito-Focus Xtreme provides 100 mg per standard two-capsule serving, and 150 mg at the three-capsule enhanced serving. Add coffee, tea and energy drinks on top and the total climbs quickly.
- Take it with food, early in the day, as the label directs.
- Don't double up. If you take L-theanine on its own as well, count both. Our single L-Theanine capsule provides 300 mg.
- Judge it over several days, not one. Responses vary and the studies measured short windows after a dose.
Who it's not for
Caffeine-containing products are not intended for:
- anyone under 18
- pregnant or breastfeeding women
- people sensitive to caffeine
If you take medication or have a known medical condition, talk to a healthcare professional first. Stop use if you get any adverse reaction.
Frequently asked questions
Does L-theanine cancel out caffeine?
In one low-dose trial it reduced caffeine's measured effects [5]. In others the combination improved task accuracy [1][3]. It depends on dose and test, which is why the evidence is described as mixed.
What ratio is most commonly used?
Many trials used roughly two parts L-theanine to one part caffeine, such as 100 mg with 50 mg [1][3]. Mito-Focus Xtreme's 200 mg to 100 mg follows the same ratio.
How long do the effects last?
The trials tested windows of roughly 30 to 90 minutes after a single dose, so there's no tested timeline for the complete formula.
Can I take L-theanine and coffee?
Studies used caffeine in tea-like and supplement doses. If you do combine them, count your total caffeine, because a cup of coffee adds to the amount in the capsules.
Is it safe to take every day?
The label direction for Mito-Focus Xtreme is two capsules daily with food, early in the day. Don't exceed the recommended dose, and check with a healthcare professional if you have a medical condition.
Where to find it
L-theanine is available on its own as MitoGenix L-Theanine, and alongside caffeine in Mito-Focus Xtreme. For the full breakdown of that stack, read our guide: Nootropic Stack for Focus: What's in Mito-Focus Xtreme.
References
- 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. https://pubmed.ncbi.nlm.nih.gov/18681988/
- Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB. The effects of L-theanine, caffeine and their combination on cognition and mood. Biol Psychol, 2008. https://pubmed.ncbi.nlm.nih.gov/18006208/
- Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci, 2010. https://pubmed.ncbi.nlm.nih.gov/21040626/
- Rogers PJ, Smith JE, Heatherley SV, Pleydell-Pearce CW. Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. Psychopharmacology, 2008. https://pubmed.ncbi.nlm.nih.gov/17891480/
- Dodd FL, Kennedy DO, Riby LM, Haskell-Ramsay CF. A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood. Psychopharmacology, 2015. https://pubmed.ncbi.nlm.nih.gov/25761837/
- 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. Nutr Rev, 2014. https://pubmed.ncbi.nlm.nih.gov/24946991/
- Payne ER, Aceves-Martins M, Dubost J, Greyling A, de Roos B. Effects of tea (Camellia sinensis) or its bioactive compounds L-theanine or L-theanine plus caffeine on cognition, sleep, and mood in healthy participants: a systematic review and meta-analysis of randomized controlled trials. Nutr Rev, 2025. https://pubmed.ncbi.nlm.nih.gov/40314930/
- Matyus RO, Szikora Z, Bodo D, et al. Promising, but not completely conclusive: the effect of L-theanine on cognitive performance based on the systematic review and meta-analysis of randomized placebo-controlled clinical trials. J Clin Med, 2025. https://pubmed.ncbi.nlm.nih.gov/41227106/
- Gerolymos C, Saddier E, Boyer L, Fond G. Cognitive and affective effects of L-theanine: a systematic review and meta-analysis of 31 randomized trials. Mol Psychiatry, 2026. https://pubmed.ncbi.nlm.nih.gov/42410082/
This health supplement is not intended to diagnose, treat, cure or prevent any disease. This unregistered medicine has not been evaluated by SAHPRA for its quality, safety or intended use. Health supplements are intended only to complement your diet.
