“L-theanine cancels out caffeine's negative effects.”
L-theanine does not cancel out caffeine's downsides; in one trial it blunted caffeine's rise in blood pressure but not its jitters.
Adding L-theanine has not been shown to make caffeine easier on your nerves or your sleep. A theanine and caffeine product still has all of its caffeine.
If caffeine makes you jittery or keeps you up, cut back on the amount or have it earlier in the day.
In a direct test, theanine blunted caffeine's rise in blood pressure but did not reduce its jitters, and no trial has tested whether it prevents caffeine's effects on sleep. Confidence is Limited because the human studies are few and small.
L-theanine does not cancel out caffeine's downsides; in one trial it blunted caffeine's rise in blood pressure but not its jitters. A theanine and caffeine product still delivers its full dose of caffeine.
In a randomized trial, 48 healthy adults took 250 mg of caffeine, 200 mg of theanine, both, or neither. Caffeine raised alertness, jitteriness and blood pressure. Adding theanine stopped the blood pressure rise but did not change jitteriness or other moods. A 2025 review found only two small studies of jitteriness after theanine plus caffeine, and both compared it with a placebo, not with caffeine alone. The sleep studies in that review tested theanine or tea on their own, not theanine added to caffeine, and their results were mixed.
- Rogers PJ, Smith JE, Heatherley SV, Pleydell-Pearce CW. Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. Psychopharmacology. 2008;195(4):569-577. DOI: 10.1007/s00213-007-0938-1. PMID: 17891480
- Payne ER, Aceves-Martins M, Dubost J, Greyling A, de Roos B. Effects of tea (Camellia sinensis) or its bioactive compounds l-theanine or l-theanine plus caffeine on cognition, sleep, and mood in healthy participants: a systematic review and meta-analysis of randomized controlled trials. Nutrition Reviews. 2025;83(10):1873-1891. DOI: 10.1093/nutrit/nuaf054. PMID: 40314930. PMCID: PMC12422004