Short answer: Yes, with moderate evidence at best. Green tea combines caffeine with L-theanine, an amino acid studied for calm, focused attention. In small trials, the two taken together improved accuracy on a demanding attention task. Green tea drinkers have lower rates of cognitive impairment in observational studies. Most trials used isolated compounds, not tea. Drink 2-3 cups a day.

Green tea is a reasonable everyday drink for the brain, but not a proven cognitive enhancer. The trials that found benefits mostly tested isolated L-theanine and caffeine, and the dementia data are observational.

How much green tea to drink

  • 2-3 cups of brewed green tea a day: This gives some L-theanine and about 60-90 mg of caffeine in total.
  • Matcha: Ground whole-leaf tea has higher amounts of all the compounds.
  • Timing: Because of the caffeine, avoid green tea late in the day if you are sensitive.
  • L-theanine supplements: Studies used 97-400 mg a day. Supplements can interact with medicines. Ask a doctor or pharmacist first, especially if you are pregnant or breastfeeding, take medication or have a health condition.

What’s in green tea

  • L-theanine: The main brain compound in green tea. This amino acid crosses the blood-brain barrier and has been studied for calm, focused alertness.
  • Caffeine: About 30 mg per 245 ml cup, about a third of a cup of coffee.
  • EGCG (epigallocatechin gallate): The most abundant and studied catechin in green tea. It has antioxidant and anti-inflammatory effects in lab and animal studies.
  • Other catechins: Including ECG and EGC, studied mainly in the lab.

Attention and focus

In a small randomized trial (Giesbrecht 2010), 44 young adults took isolated L-theanine (97 mg) plus caffeine (40 mg) or a placebo. The combination improved accuracy on a task-switching test and self-rated alertness, and reduced tiredness. It did not change visual search, reaction time or mental rotation.

People often say L-theanine smooths out caffeine’s buzz, but this has not been well established. A cup of brewed tea usually contains less L-theanine than the doses used in these studies. For more on caffeine itself, see caffeine and cognition and foods for focus.

Stress and mood

In a 4-week crossover trial of 30 healthy adults (Hidese 2019), 200 mg a day of L-theanine reduced stress-related symptoms and improved sleep quality scores compared with placebo.

In another trial (Ritsner 2011), 400 mg a day added to antipsychotic treatment reduced anxiety symptoms in 60 people with schizophrenia. That result can’t be applied to anxiety in the general population. Our page on diet and anxiety covers the wider evidence.

Dementia risk

A meta-analysis of 18 observational studies with 58,929 participants (Zhou 2026) found that green tea drinkers had about 37% lower odds of cognitive impairment. These studies can’t show that tea caused the difference.

Proposed explanations include EGCG’s antioxidant and anti-inflammatory effects and L-theanine’s effects in cell and animal studies. Animal studies also suggest EGCG may raise BDNF, a protein involved in learning and memory. This has not been shown in humans.

Who should be careful

  • Caffeine sensitivity: Even the moderate caffeine in green tea can cause insomnia, anxiety or jitters in sensitive people.
  • Iron: Green tea catechins can reduce absorption of iron from plant foods. If you are at risk of iron deficiency, don’t drink it with iron-rich meals.
  • Thyroid: Very high intake of green tea extracts has been linked to thyroid problems in some studies. Moderate tea drinking is safe.
  • Medication interactions: Green tea may interact with some medications, including blood thinners, beta-blockers and chemotherapy. Ask your doctor.
  • EGCG supplements: Concentrated green tea extracts have been linked to rare cases of liver toxicity. The European Food Safety Authority (EFSA 2018) found that 800 mg or more of EGCG a day from supplements raised liver enzymes in trials. Traditionally brewed tea is generally considered safe, so stick to brewed tea.

Sources

  • EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS), et al. (2018). Scientific opinion on the safety of green tea catechins. EFSA Journal, 16(4), e05239. doi:10.2903/j.efsa.2018.5239
  • Giesbrecht, T., Rycroft, J. A., Rowson, M. J., & De Bruin, E. A. (2010). The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutritional Neuroscience, 13(6), 283–290. doi:10.1179/147683010X12611460764840
  • Hidese, S., et al. (2019). Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: A randomized controlled trial. Nutrients, 11(10), 2362. doi:10.3390/nu11102362
  • Ritsner, M. S., et al. (2011). L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: An 8-week, randomized, double-blind, placebo-controlled, 2-center study. The Journal of Clinical Psychiatry, 72(1), 34–42. doi:10.4088/JCP.09m05324gre
  • Zhou, S., Zhu, Y., Ren, N., Wu, M., & Liu, Y. (2026). The association between green tea consumption and cognitive function: A meta-analysis of current evidence. Neuroepidemiology, 60(1), 178–199. doi:10.1159/000543784
  • USDA FoodData Central, SR Legacy: Beverages, tea, green, brewed, regular (FDC ID 171917). fdc.nal.usda.gov