Interaction fact sheet · Synergy
Caffeine and L-theanine
Compatible, studied combination.
Several trials show a small improvement in attention and alertness with the combination, at doses close to those in a cup of strong tea. The effect remains modest and short-lived.
What the trials show
Haskell and colleagues compared 250 mg of L-theanine, 150 mg of caffeine, their combination and a placebo in a randomized crossover trial. The combination improved accuracy on the sustained attention test (RVIP), sped up simple reaction time and numeric working memory, and increased perceived alertness while reducing fatigue and headaches. Their conclusion: the combination has a different pharmacological profile from caffeine alone.
Owen and colleagues tested 50 mg of caffeine with or without 100 mg of L-theanine in 27 healthy volunteers. The combination improved speed and accuracy on the attention-switching test after 60 minutes and reduced susceptibility to distractions in the memory test. This trial was conducted in an industrial laboratory (Unilever R&D), so the results should be read with the usual critical perspective applied to studies funded by an interested party.
Studied ratio and timing
In the trials, effects appear between 60 and 90 minutes after intake. The tested protocols are 100 mg of theanine with 50 mg of caffeine (Owen) and 250 mg of theanine with 150 mg of caffeine (Haskell). These are not prescriptions: they are the only two dosages supported by published data.
Limits
The samples are small, and the effects were measured in the short term after a single dose. We do not know whether the benefits persist with daily use or how they vary with your caffeine sensitivity. Theanine alone showed no cognitive benefit in these trials: if you take it on its own in the evening to relax, that is a different use, with different evidence to examine.
For practical guidance (timing during your day, total caffeine dose, evening cutoff), see the protocol sheet caffeine and L-theanine stack and the caffeine calculator.
Main sources
- 01Haskell CF et al. The effects of L-theanine, caffeine and their combination on cognition and mood. Biological Psychology, 2008. PubMed 18006208
- 02Owen GN et al. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutritional Neuroscience, 2008. PubMed 18681988
Frequently Asked Questions (FAQ)
What caffeine-to-theanine ratio was used in the trials?
Owen and colleagues tested 100 mg of L-theanine with 50 mg of caffeine, a ratio of 2 to 1. Haskell and colleagues tested 250 mg of theanine with 150 mg of caffeine. Both protocols showed effects on attention, without establishing an ideal ratio.
Does L-theanine alone improve cognition?
Not in any demonstrated way. In the Haskell trial, theanine alone increased headache ratings and worsened performance on a calculation task, while the combination improved reaction speed and working memory. The effects apply to the combination, not to theanine alone.