Weak evidence · Sleep & stress
L-theanine
Attention and alertness, especially together with caffeine
Weak evidence
Mostly small studies, animal trials or conflicting results. Not worth your money as a foundation.
A meta-analysis of 11 placebo-controlled studies (Camfield et al.) found moderate effects of caffeine together with L-theanine on alertness and attention switching in the first two hours. A more recent review cautiously concludes that theanine, alone or with caffeine, possibly improves attention and mood, with uncertainty about the size of the effect.
- Dosage
- 100–400 mg in the studies, often together with caffeine
- Timing
- Together with your coffee; effects were measured 40 to 70 minutes after intake
- Approx. price
- €5–12 per month
Watch out
The studies measured attention and mood, not sports performance. In the analysis the caffeine dose seemed to matter more than the theanine dose.
Frequently asked questions about supplements
How much L-theanine per day?
100–400 mg in the studies, often together with caffeine
When should you take L-theanine?
Together with your coffee; effects were measured 40 to 70 minutes after intake
Does L-theanine really work?
Weak evidence. Mostly small studies, animal trials or conflicting results. Not worth your money as a foundation.
What does L-theanine cost?
€5–12 per month
Basics first, then the tub
Supplements are called supplements because they add to something. Sleep, a protein intake that hits your protein calculator , a programme where you lift progressively heavier and enough food together do a hundred times more than the best-researched item on this list. Once those are in place, creatine, caffeine and vitamin D in winter are the three you can spend money on with a clear conscience — for less than ten euros a month combined.
Sources
- Camfield DA et al. (2014). Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis. Nutr Rev. (meta-analysis, 11 studies)
More supplements in this category
Last updated: October 2026
This page summarises scientific research and is not medical advice. If you take medication, are pregnant or have a liver, kidney or thyroid condition, discuss supplements with your doctor or pharmacist — even the innocent-looking ones.
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