Does green tea help improve your memory or concentration?

Caffeine, one of the active compounds in green tea, demonstrably improves alertness and reaction time, even at low doses. This effect is well supported and applies to demanding tasks that require sustained concentration over a longer period.

The combination of caffeine and L-theanine (the other characteristic component of green tea) outperforms either substance on its own. A placebo-controlled crossover study showed that this combination improved accuracy in information processing, shortened reaction time, and reduced self-reported mental fatigue. A systematic review of 21 studies confirms that green tea as a whole has a positive, modest effect on memory, attention, and working memory.

L-theanine alone works differently: at 200 mg, self-reported relaxation increased and it dampens the stimulating effect of caffeine. A randomised study in 50-69-year-olds also found measurable improvements in attention and working memory after a single dose of L-theanine without added caffeine. That study was, however, funded by a tea company, which makes the results somewhat less independent.

Matcha (a concentrated form of green tea) presents a more mixed picture. Drinking matcha daily for one year did not significantly change overall cognition in older adults with mild cognitive decline. A smaller 12-week study did see an improvement, but only in the female subgroup, which is less reliable. Tea companies were also financially involved in those studies.

If you suffer from headaches or are sensitive to caffeine, bear in mind the finding that L-theanine alone also caused more headache complaints in one of the studies. The effects of green tea on concentration and memory are therefore real but modest, and the greatest share of the benefit lies in the combination of caffeine and L-theanine that you simply find in a normal cup of green tea.