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L-Theanine & Caffeine: Why They’re Often Taken Together
L-theanine and caffeine are two compounds often found together in tea, capsules, and powders. Here's what each one does, how they work together, and what to know before you combine them.
Key takeaways:
- 01.
L-theanine is an amino acid found in tea leaves, while caffeine is found in coffee, tea, and cocoa.
- 02.
Third-party clinical research suggests the pair may support attention and reaction time more than either compound alone.*
- 03.
A cup of tea provides far less L-theanine than the doses used in trials, so many people turn to an L-theanine and caffeine supplement.
- 04.
For healthy adults, caffeine intake of up to 400 mg a day from all sources doesn’t raise safety concerns.
- 05.
AG1 Energy+ adds 100 mg of plant-based caffeine and 100 mg of L-theanine to AG1 Next Gen to support hours of energy and focus.*
What is L-theanine?
L-theanine is an amino acid found specifically in tea leaves, and it is best known for promoting relaxation, reducing stress, and supporting mental focus—often without causing drowsiness. The body absorbs it through the small intestine, where it reaches peak blood levels in about 45 to 50 minutes. It then crosses into the brain, which is one reason researchers study it alongside attention. Purified forms are now sold as supplements.1
What is caffeine?
Caffeine is found in coffee, tea, and cocoa. It blocks adenosine receptors in the brain, which is why it's linked with alertness and attention. It's absorbed quickly and typically peaks in the blood about an hour after you consume it.1
Benefits of combining L-theanine and caffeine
Researchers have studied the benefits of taking L-theanine with caffeine for years. Third-party clinical research* suggests the pair may support attention more than either compound alone.1,2 In one trial, the combination was linked with stronger cognitive performance and higher self-reported alertness.3 Another tested L-theanine, caffeine, and their combination side by side on cognition and mood.4
A 2025 double-blind, placebo-controlled crossover trial followed 37 healthy young adults who had stayed awake overnight. Compared with placebo, 200 mg of L-theanine plus 160 mg of caffeine was associated with greater accuracy and faster reaction times on an attention task.*1
So does taking L-theanine with caffeine support focus and concentration? Third-party research points to support for attention and reaction time, though the studies are small and measure single doses.1 These findings come from third-party research on the ingredients, not on AG1 Energy+.
Best sources of L-theanine and caffeine
Tea is the main dietary source of L-theanine, which also supplies a small amount of caffeine. A cup of tea contains about 4 to 22 mg of L-theanine and 25 to 50 mg of caffeine, depending on the variety and brew time.1 (That's well below the amounts used in most trials.1,2) Coffee supplies caffeine but no L-theanine.
So, there are three common ways to consume L-theanine with caffeine: drinking tea, which supplies both compounds in small amounts, adding an L-theanine capsule or powder to your coffee, or choosing a product that already contains both. An L-theanine and caffeine supplement delivers measured amounts in one dose. In fact, the 2025 trial's doses were chosen to match many commercial supplements and functional beverages.1
Where AG1 Energy+ fits
AG1 Energy+ is the AG1 Next Gen formula with 100 mg of caffeine from green coffee bean extract and 100 mg of L-theanine added to each Travel Pack, to support energy, focus, and mental clarity.*
AG1 Energy+ includes B vitamins (B1, B2, B3, B5, B6, B7, B9, and B12)—cofactors that help your body unlock energy from the food you eat—alongside 77+ vitamins, minerals, and whole-food-sourced ingredients, including beetroot, acerola cherry, papaya, pineapple, and matcha.*
How much L-theanine should I take with caffeine?
Trials offer examples, not recommendations. There is no single established L-theanine caffeine ratio. The 2025 trial used 200 mg of L-theanine with 160 mg of caffeine—about 1.25 to 1.1
AG1 Energy+ pairs 100 mg of each, a 1 to 1 ratio. Follow the serving size on the label, and ask your healthcare provider if you're unsure.
When should I take L-theanine with caffeine?
Most people take them when they'd normally have caffeine, such as in the morning. L-theanine peaks in the blood in about 45 to 50 minutes and caffeine in about an hour, so both arrive on a similar timeline.1 Earlier in the day is the safer window, since caffeine may affect your ability to fall asleep.
Can you take L-theanine and caffeine every day?
Many people do, as daily caffeine and L-theanine intake is generally recognized as safe for most healthy adults. Count your coffee, tea, and supplements together, since the 400 mg daily figure applies to caffeine from all sources.5 The 2025 researchers also noted that habitual use may reduce attention benefits over time.1
Does L-theanine make caffeine less effective?
Research points the other way. Trials report that the pair affects attention more positively than either compound alone.1,2
Potential side effects and considerations
High caffeine intake is associated with jitters, nervousness, irritability, a faster heart rate, and trouble sleeping. L-theanine is generally well tolerated in human studies.1 There has been substantiation that L-theanine can reduce caffeine jitters.6 If caffeine leaves you feeling unsettled, try a lower amount or talk with your healthcare provider.
Putting it together
Talk with your healthcare provider before adding either compound if you take medications. AG1 Energy+ contains 100 mg of caffeine and 100 mg of L-theanine per serving. Like all AG1 products, it's not recommended for anyone under 18 or for pregnant or breastfeeding women.
For more ways to support your day, visit our Energy Production health guide. To see where AG1 Energy+ sits in the lineup, browse the full range in the AG1 shop.*
References:
- Nawarathna GS, Ariyasinghe DI, Dassanayake TL. High-dose L-theanine–caffeine combination improves neurobehavioural and neurophysiological measures of selective attention in acutely sleep-deprived young adults: a double-blind, placebo-controlled crossover study. Br J Nutr. 2025;134(3):195-204. doi:10.1017/S0007114525104169
- Kahathuduwa CN, Dassanayake TL, Amarakoon AMT, Weerasinghe VS. Acute effects of theanine, caffeine and theanine-caffeine combination on attention. Nutr Neurosci. 2017;20(6):369-377. doi:10.1080/1028415X.2016.1144845
- Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci. 2010;13(6):283-290. doi:10.1179/147683010X12611460764840
- Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB. The effects of L-theanine, caffeine and their combination on cognition and mood. Biol Psychol. 2008;77(2):113-122. doi:10.1016/j.biopsycho.2007.09.008
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the safety of caffeine. EFSA J. 2015;13(5):4102. doi:10.2903/j.efsa.2015.4102
- 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. 2007;195(4):569-577. doi:10.1007/s00213-007-0938-1
