A fixed combination of caffeine with L-theanine, the amino acid found in tea leaves, usually in a one-to-two ratio. It is sold on the premise that theanine removes the jitteriness of caffeine while keeping the alertness.
This combination is one of the more plausible stacks in the nootropic category because it has an obvious natural precedent: tea contains both, and the subjective experience of tea differs from that of coffee at matched caffeine. The trials are modest. Several small studies report that the combination improves attention-switching and reduces distractibility more than caffeine alone, and some report lower self-rated tiredness or jitteriness. The effects are small, the studies are short and often industry-funded, and a good part of the alerting effect belongs to the caffeine. Theanine on its own has a weak evidence base for relaxation without sedation.
Regulation: Sold as a dietary supplement in the US with no pre-market efficacy review. Theanine is authorised as a food ingredient in Japan and permitted in supplements in most markets. The caffeine component carries all the usual caffeine considerations.
What the research used
The amounts, forms and durations published trials of Caffeine with L-theanine actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Attention and cognitive trials
50–100 mg
Limited
Caffeine with 100–200 mg L-theanine, single dose · Acute, single administration
The combination used in most published studies. Doses at the low end of caffeine were chosen deliberately, and the results do not necessarily hold at the 200 mg or higher caffeine doses in commercial products.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
Each timing below was actually compared against an alternative in a trial, which is unusual.
🌅Morning
Moderate
Taken earlier in the day for the same reason as caffeine alone: the sleep disruption from a late dose is a measured pharmacological effect, and theanine does not shorten caffeine's half-life.
Timing was tested. A trial compared this window against another and reported a difference.
The evidence in depth
Best supported: Moderate
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
Small acute trials report improvements in attention-switching accuracy and reduced susceptibility to distraction with the combination, with some finding advantages over caffeine alone. The studies are short, small and often supported by theanine manufacturers, and the alerting component is largely caffeine.
What may be going on: Theanine crosses the blood-brain barrier and increases alpha wave activity, and is thought to moderate the arousal caffeine produces through adenosine antagonism.
Moderate evidence. Several human studies point the same way, with real caveats.
Theanine alone has small trials reporting reduced subjective stress and lower cortisol responses. Whether it meaningfully offsets caffeine-induced jitteriness has been reported subjectively rather than demonstrated consistently.
Limited evidence. Early human work, or mostly lab and animal research.
Deep research mode adds each paper’s own conclusion and stated limitations.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Worth knowing
It is still caffeine
Every caffeine consideration applies unchanged: dependence, withdrawal, sleep disruption from late doses, arrhythmia risk in susceptible people, pregnancy limits and drug interactions through CYP1A2. Theanine does not change how the caffeine is cleared.
Theanine has been reported to lower blood pressure modestly in some studies, while caffeine raises it acutely. Combining either with antihypertensives or with sedatives makes the net effect harder to predict.
Worth knowing
Trial doses are lower than product doses
Most studies used 50 to 100 mg of caffeine with theanine. Pre-workout and nootropic products commonly contain two to four times that, at which point the smoothing effect attributed to theanine has not been tested.
Avoid
Not for children or in pregnancy
Concentrated caffeine products are inappropriate for children and adolescents, and pregnancy caffeine limits apply to the combination as to any other source.
In the food catalogue
The whole-food form, where one exists. The evidence for a concentrated extract rarely transfers to the food, or the other way round — these are cross-links, not equivalents.