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All 48 studies in the study browser
Included: human randomized controlled trials, systematic reviews and meta-analyses on caffeine and L-theanine indexed in PubMed. A PubMed search on October 15, 2026 returned 97 records. 48 remain after excluding protocols, retractions, comments and papers that did not study caffeine and L-theanine as the intervention or exposure. Below are all 7 reviews and the 25 highest-scored individual studies. The study browser has the rest.
Scores run from 1 to 5 and rate study design only. The rules and reason codes are on Study Scores. Each finding restates the abstract's own conclusion.
Back to Caffeine and L-theanine
| Score | Study | Design, n | Finding |
|---|---|---|---|
| 5 (MA +large) | Gerolymos, 2026 | Meta-analysis, 31 studies | L-theanine is safe and shows a robust short-term benefit on attention in healthy adults, with a potential antidepressant effect warranting confirmation in high-quality trials, especially in clinical populations. |
| 4 (MA) | Payne, 2025 | Meta-analysis | This meta-analysis provides evidence that theanine plus caffeine, and theanine alone, could be beneficial for cognitive and mood outcomes. More research using tea beverages or tea-equivalent bioactive doses and research in... |
| 4 (MA) | Bulman, 2025 | Meta-analysis, 10 studies, n=897 | The findings indicate the potential use of L-theanine in the management of sleep disturbances; however, the lack of studies on "pure" L-theanine warrants further investigation. Future studies are needed to determine the adequate... |
| 4 (MA) | Camfield, 2014 | Meta-analysis, 11 studies | Evidence of moderate effect sizes in favor of combined caffeine and L-theanine in the first 2 hours postdose were found for outcome measures Bond-Lader alertness, attentional switching accuracy, and, to a lesser extent, some... |
| 3 (SR) | Cotter, 2026 | Systematic review, 11 studies | Among the included trials, beneficial effects were reported on both objective and participant-reported outcomes, including measures linked to sleep latency, maintenance and efficiency, perceived sleep satisfaction and feelings of... |
| 3 (SR) | Moshfeghinia, 2024 | Systematic review, 11 studies | The findings from this systematic review suggest that LT supplementation significantly reduced psychiatric symptoms more effectively than control conditions in individuals with schizophrenia, anxiety disorders, and ADHD. However,... |
| 3 (SR) | Williams, 2020 | Systematic review, 9 studies | Our findings suggest that supplementation of 200-400 mg/day of L-THE may assist in the reduction of stress and anxiety in people exposed to stressful conditions. Despite this finding, longer-term and larger cohort clinical... |
| Score | Study | Design, n | Finding |
|---|---|---|---|
| 4 (RCT +blind) | Nematizadeh, 2023 | RCT, n=95 | Findings in this study suggest L-theanine as a relatively safe and effective adjuvant therapy for moderate to severe OCD. |
| 4 (RCT +blind) | Shamabadi, 2023 | RCT, n=50 | L-theanine adjunct to sertraline outperforms placebo in treating MDD in a safe manner. Further long-term, large-scale studies are recommended to confirm this evidence. |
| 4 (RCT +blind) | Dassanayake, 2023 | RCT, n=32 | Consistent with our hypothesis, these findings suggest that L-theanine significantly improves attention in simple visuomotor tasks, but not in more complex sustained attention tasks, or executive control tasks that require... |
| 4 (RCT +blind) | Furushima, 2022 | RCT, n=120 | However, the difference between theanine/arginine and theanine groups, was not statistically significant (p=0.74). From this study, no clear conclusion could be drawn regarding the potentiating effect of theanine and arginine... |
| 4 (RCT +blind) | Noah, 2022 | RCT, n=49 | Mg-Teadiola is effective in managing stress in otherwise healthy individuals. Its beneficial effects on sleep and pain perception need further investigation. |
| 4 (RCT +blind) | Rizzo, 2022 | RCT, n=34 | Supplementation of both L-Theanine and Vitamin B6 may help in the treatment of tic disorders associated with anxious symptoms. Between-group differences in clinician-rated severity did reach statistical significance only for tics. |
| 4 (RCT +blind) | Hidese, 2019 | RCT, n=30 | Stratified analyses revealed that scores for verbal fluency (p = 0.002), especially letter fluency (p = 0.002), increased after L-theanine administration, compared to the placebo administration, in individuals who were... |
| 4 (RCT +blind) | Lyon, 2011 | RCT, n=98 | This study demonstrates that 400 mg daily of L-theanine is safe and effective in improving some aspects of sleep quality in boys diagnosed with ADHD. Since sleep problems are a common co-morbidity associated with ADHD, and... |
| 4 (RCT +blind) | Ritsner, 2011 | RCT, n=60 | L-theanine augmentation of antipsychotic therapy can ameliorate positive, activation, and anxiety symptoms in schizophrenia and schizoaffective disorder patients. Further long-term studies of L-theanine are needed to substantiate... |
| 4 (RCT +blind) | Giesbrecht, 2010 | RCT, n=44 | There were no significant effects on other cognitive tasks, such as visual search, choice reaction times, or mental rotation. The present results suggest that 97 mg of L-theanine in combination with 40 mg of caffeine helps to... |
| 4 (RCT +blind) | Rogers, 2008 | RCT, n=48 | Theanine is a physiologically and behaviourally active compound and, while it is unclear how its effects might explain perceived differences between tea and coffee, evidence suggests that it may be useful for reducing raised blood pressure. |
| 3 (RCT +blind -n<30) | McAllister, 2024 | RCT, n=28 | These data demonstrate that ingestion of L-theanine or L-tyrosine does not impact markers of stress in response to a MSC but may impact cognitive performance. This study was pre-registered as a clinical trial ("Impact of... |
| 3 (RCT +blind -n?) | Shamabadi, 2023 | RCT | L-Theanine adjunct to risperidone safely and tolerably outperformed adjunctive placebo for schizophrenia, and promising evidence indicated its effects on primary negative symptoms, which need to be scrutinized in further studies. |
| 3 (RCT +blind -n?) | Baba, 2021 | RCT | Our study indicated that l-theanine may contribute to improving attention, thus enhancing working memory and executive functions. Clinical Trial No.: UMIN000033812. |
| 3 (RCT +blind -n<30) | Juszkiewicz, 2019 | RCT, n=10 | Despite the decrease in the number of some cytotoxic cells (CTLs) and an increase in the proportion of Tregs to CTLs, supplementation with LTE seems to exert a beneficial effect on a disrupted Th1/Th2 balance in elite athletes,... |
| 3 (RCT +blind -pilot) | Sarris, 2019 | RCT, n=46 | No significant cognitive effects (trail making time and the modified emotional Stroop) were revealed. While this preliminary study did not support the efficacy of L-theanine in the treatment of anxiety symptoms in GAD, further... |
| 3 (RCT +blind -n<30) | Kahathuduwa, 2018 | RCT, n=9 | Factorial analysis suggested that l-theanine and caffeine seem to have a synergistic action in decreasing mind wandering. Therefore, our hypothesis is that l-theanine and caffeine may be decreasing deviation of attention to... |
| 3 (RCT +blind -n?) | White, 2016 | RCT | This change in resting state alpha oscillatory activity was not correlated with the change in subjective stress response or the cortisol response, suggesting further research is required to assess the functional relevance of... |
| 3 (RCT +blind -n?) | Dodd, 2015 | RCT | Combining 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... |
| 3 (RCT +blind -n<30) | Unno, 2013 | RCT, n=20 | Stressful condition increased the level of sAA that was essentially affected by individual trait anxiety. The low levels of pre-practice sAA and subjective stress in the theanine-group suggest that theanine intake suppressed... |
| 3 (RCT +blind -n?) | Yoto, 2012 | RCT | The findings above denote that L-theanine not only reduces anxiety but also attenuates the blood-pressure increase in high-stress-response adults. |
| 3 (RCT +blind -n?) | Foxe, 2012 | RCT | This effect was not changed by addition of theanine in the combined treatment. Theanine alone did not affect alpha-band activity. |
| 3 (RCT +blind -n<30) | Park, 2011 | RCT, n=11 | Brain theta waves, an indicator of cognitive alertness, were increased significantly in the temporal, frontal, parietal, and occipital areas after 3 hours in the eye-open and reading states. Therefore, this study suggests that... |
| 3 (RCT +blind -n?) | Einöther, 2010 | RCT | The combination of L-theanine and caffeine significantly improved attention on a switch task as compared to the placebo, while subjective alertness and intersensory attention were not improved significantly. The results support... |
| 3 (RCT +blind -n<30) | Owen, 2008 | RCT, n=27 | The L-theanine and caffeine combination improved both speed and accuracy of performance of the attention-switching task at 60 min, and reduced susceptibility to distracting information in the memory task at both 60 min and 90... |