Trial reportPsychopharmacology2015
A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood.
Trial report in Psychopharmacology, 2015. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 46 papers, 4 of them syntheses that pooled it.
What it found
Each row is one number read from the abstract, on the scale the paper reported it, with its interval. Left of the dashed line favours the treatment, right favours the comparator. Under each row is the sentence it came from. New to these charts? A ten-minute tutorial.
The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.
The trial behind it
Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.
Neither the registry nor the abstract names a trial number. If this is a trial report, that itself is worth knowing.
Who cites it
46 citing papers in PubMed, 4 syntheses or guidelines pooled it, 91 citations in OpenAlex.
- Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials.Molecular psychiatry · 2026Pooled it
- Pooled it
- A systematic review and meta-analysis of the acute effect of caffeine on attention.Psychopharmacology · 2025Pooled it
- Association between tea consumption and risk of cognitive disorders: A dose-response meta-analysis of observational studies.Oncotarget · 2017Pooled it
- Comparable improvements in selective, but not sustained, attention in response to a multi-ingredient nootropic formulation when compared with caffeine.European journal of nutrition · 2026Trial
- Performance-enhancing effects of caffeine and L-Theanine among Iranian elite wrestlers: a focus on cognitive and specific physical performance.Journal of the International Society of Sports Nutrition · 2025Trial
- Mixed Tree Nuts, Cognition, and Gut Microbiota: A 4-Week, Placebo-Controlled, Randomized Crossover Trial in Healthy Nonelderly Adults.The Journal of nutrition · 2023Trial
- Trial
- Effects of acute caffeine, theanine and tyrosine supplementation on mental and physical performance in athletes.Journal of the International Society of Sports Nutrition · 2019Trial
- The Acute Effects of Caffeinated Black Coffee on Cognition and Mood in Healthy Young and Older Adults.Nutrients · 2018Trial
- Trial
- Spearmint Extract Improves Working Memory in Men and Women with Age-Associated Memory Impairment.Journal of alternative and complementary medicine (New York, N.Y.) · 2018Trial
- Trial
- Cognitive and mood improvements following acute supplementation with purple grape juice in healthy young adults.European journal of nutrition · 2017Trial
- Compositional Diversity and Functional Interactions of Bioactive Compounds in Japanese Green Tea: Focus on Matcha, Sencha, and Gyokuro.Molecules (Basel, Switzerland) · 2026Review
- Caffeine in cerebrovascular research: To withdraw or not to withdraw?Experimental physiology · 2026Article
- Beverage consumption patterns and primary dysmenorrhea among women of reproductive age: a population-based study in Beijing, China.Frontiers in nutrition · 2026Article
- Effects of L-theanine on cognition, mood and sleep: evidence from human trials.Frontiers in nutrition · 2026Review
- Effect ofIBRO neuroscience reports · 2025Article
- Promising, but Not Completely Conclusive-The Effect of l-Theanine on Cognitive Performance Based on the Systematic Review and Meta-Analysis of Randomized Placebo-Controlled Clinical Trials.Journal of clinical medicine · 2025Review
Corrections and comments
PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.
Authors and funding
4 authors at 1 institution in 1 country.
Funding
No grant is acknowledged in the PubMed record.
Abstract
rationaleEvidence suggests interactive effects of the tea components caffeine and L-theanine on behaviour, yet no data exists exploring the impact of the two on cerebral blood flow (CBF).
objectivesThe current placebo-controlled, double-blind, counterbalanced, crossover study examined the effects of caffeine and L-theanine on CBF and extended previous cognitive and mood findings by using lower doses than previous studies of a similar methodology, which more closely reflect the ratios present in tea.
methodsTwelve habitual consumers and 12 non-habitual consumers of caffeine each received 75 mg caffeine, 50 mg L-theanine, 75 mg caffeine plus 50 mg L-theanine, and placebo in a counterbalanced order across four separate visits. CBF was measured via near-infrared spectroscopy with cognition and mood assessed at baseline and 30 min post-dose. Salivary caffeine and peripheral haemodynamics were co-monitored.
resultsCaffeine reduced oxygenated haemoglobin (oxy-Hb), increased deoxygenated haemoglobin (deoxy-Hb), improved performance on attention tasks and increased overall mood ratings. Increases in deoxy-Hb following caffeine were more pronounced in non-consumers. Some evidence for increased deoxy-Hb remained when caffeine was combined with L-theanine, but this effect was attenuated and the effects of caffeine on oxy-Hb, cognition and mood were eradicated.
conclusionsCombining L-theanine with caffeine, at levels and ratios equivalent to one to two cups of tea, eliminated the vasoconstrictive effect and behavioural effects of caffeine. This supports previous findings of an interaction between these substances, despite a lack of effects of L-theanine in isolation. However, at the levels tested here, this did not lead to a positive impact on behaviour.
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Registered trials
Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.