Caffeine or L-Theanine: What's the Difference

Caffeine and L-theanine are found in the same cup of tea, but they act almost in opposite ways. The editorial team explains how each substance affects the brain, what the research shows separately and in combination, and why it is incorrect to regard them as competitors.

Two substances from one cup of tea

Caffeine and L-theanine are often mentioned together because both are naturally found in tea. However, these are substances of fundamentally different nature and action: caffeine is a stimulant, while L-theanine is an amino acid associated with a state of calm focus. Comparing them as "competitors" is not entirely correct, and the editorial team explains why.

Caffeine is an alkaloid from the methylxanthine group, found in coffee, tea, cocoa, guarana and mate. It is the most widespread psychoactive substance in the world, with well-studied effects on the brain, heart and muscle work.

L-theanine (N-ethyl-L-glutamine) is a non-proteinogenic amino acid found almost exclusively in the tea leaves of Camellia sinensis and in some mushrooms. In structure it is similar to glutamate - the main excitatory neurotransmitter of the brain - and to glutamine.

Tea contains both substances, and many researchers suggest that it is precisely their combination that explains why tea subjectively "invigorates more gently" than coffee with a similar amount of caffeine.

Mechanism of action: stimulation versus modulation

Caffeine blocks adenosine receptors A1 and A2A. Adenosine is a natural "fatigue signal," so blocking its action reduces drowsiness, increases alertness and lessens the subjective feeling of effort during training. In parallel, adrenaline levels rise and heart rate and blood pressure increase.

L-theanine acts quite differently. It crosses the blood-brain barrier and, according to mostly experimental studies, interacts with glutamate receptors and may also affect levels of GABA, dopamine and serotonin in certain areas of the brain. It is not classed among stimulants or sedatives.

One of the most cited findings is theanine's effect on the brain's alpha rhythm. Nobre and colleagues (2008) described an increase in alpha activity on the EEG after taking 50 mg of theanine, which is associated with a state of relaxed attentiveness. Importantly, this is not drowsiness but rather calm readiness.

Thus caffeine "pushes" the nervous system, while theanine rather gently modulates it. This explains why they are studied not as alternatives but as components of a combination.

What the research shows

The effects of caffeine on physical and mental performance are confirmed by a large number of studies. The 2020 "umbrella" review by Grgic and colleagues summarized 21 meta-analyses and concluded that there is a small to moderate ergogenic effect across a wide range of loads.

For theanine as a separate substance the data are much more modest. No convincing effect on physical performance has been shown. As for cognitive functions and mood, the results are inconsistent: some studies record a slight reduction in subjective tension, others no noticeable effect.

The most interesting data concern the combination. In the 2008 study by Owen and colleagues, the combination of 100 mg of theanine and 50 mg of caffeine improved the accuracy of attention switching compared with placebo. Giesbrecht and colleagues in 2010, with doses of 97 mg of theanine and 40 mg of caffeine, also found better accuracy in attention-switching tasks.

The 2014 systematic review by Camfield and colleagues summarized that the combination of caffeine and theanine in moderate doses improves attention measures in the first two hours after intake. However, some of the studies were funded by tea manufacturers, which is worth taking into account.

Comparison table

The editorial team brought the key differences between the two substances together in a table.

Interestingly, in the 2008 study by Rogers and colleagues theanine suppressed the increase in blood pressure caused by caffeine. This is one of the few studies that gives a physiological basis for the idea that theanine "softens" the stimulating action of caffeine.

In the classic 2008 study by Haskell, higher doses were used - 250 mg of theanine and 150 mg of caffeine. The combination improved a number of measures of reaction speed and memory, although some of the effects were due primarily to caffeine.

So, according to the research, caffeine is responsible for "energy" and stimulation, while theanine is responsible for possibly smoothing out unwanted effects and, probably, for part of the benefits in attention.

Safety

Caffeine is safe for healthy adults up to 400 mg per day according to the EFSA assessment, and up to 200 mg per day for pregnant women. Excessive doses cause anxiety, tremor, tachycardia and insomnia; concentrated caffeine powders are dangerous because of the risk of overdose.

L-theanine has a favorable safety profile at the doses studied: no serious side effects have been described. However, people who take blood-pressure-lowering drugs or sedatives should clear intake with a doctor, since an additive effect is possible.

• Do not regard theanine as an "antidote" to caffeine overdose - it does not remove the risks of large doses.
• Pregnant and breastfeeding women are better off not taking supplemental theanine because of the lack of data.
• For athletes: neither substance is banned by WADA; caffeine is on the monitoring program.

In general, from a safety standpoint, the main attention should be paid to the caffeine dose, while theanine is a relatively neutral supplement.

Editorial conclusions

Caffeine and L-theanine are not alternatives but substances with opposite vectors of action: the first stimulates, the second promotes calm focus.

An ergogenic effect is proven only for caffeine. Theanine on its own does not increase physical performance, but in combination with caffeine it may improve attention and soften certain unwanted effects.

The most interesting data concern precisely the combination of these substances in moderate doses - the way it happens in a cup of tea, but in a more concentrated form.

Read also our materials on caffeine and anxiety, on caffeine before competitions, and on comparing caffeine with paraxanthine.

References

1. Fredholm BB, Bättig K, Holmén J, Nehlig A, Zvartau EE. Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. Pharmacol Rev. 1999;51(1):83–133.
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;17(Suppl 1):167–168.
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;11(4):193–198.
4. 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;13(6):283–290.
5. 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;77(2):113–122.
6. 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;72(8):507–522.
7. 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 (Berl). 2008;195(4):569–577.
8. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific Opinion on the safety of caffeine. EFSA Journal. 2015;13(5):4102.