Caffeine and L-Theanine: What the Studies Show and How Much to Take
The best-studied range is 97-250 mg L-theanine with 40-150 mg caffeine. Here is what four primary sources found, and what they did not.
Short answer
The best-studied dose is roughly 100 to 250 mg of L-theanine with 40 to 150 mg of caffeine, about 1.7 to 2.4 parts theanine per part caffeine. In small placebo-controlled trials, that combo improved alertness and accuracy on attention-switching tasks within the first one to two hours. It did not improve everything. Below is what four primary sources found and what to do with it.
Most posts about this combo just say it's smoother than coffee. I wanted to know what the research actually measured, so I read four studies on PubMed. They're small and short, and I'll point out where they stop being useful.
What is the caffeine and L-theanine combination?
Caffeine is a stimulant found in coffee, tea, and cacao. L-theanine is an amino acid found in tea. Because tea contains both, researchers started testing them together to see whether the pair behaves differently from caffeine alone.
The FDA lists typical caffeine content per 12 fluid ounces at 37 mg for green tea, 71 mg for black tea, and 113 to 247 mg for regular brewed coffee. So a cup of tea is a low-dose version of this combination, and coffee has caffeine with no theanine at all.
What did the studies find?
Four sources carry most of the weight. All four examined healthy adults, and all of the trials measured short-term effects after a single dose.
- Haskell et al. (2008, Biological Psychology) gave 250 mg L-theanine and 150 mg caffeine, alone and combined, in a double-blind crossover study. The combination improved rapid visual information processing accuracy, sped up simple reaction time and numeric working memory reaction time, and raised self-rated alertness. It also cut self-rated "headache" and "tired" scores.
- Owen et al. (2008, Nutritional Neuroscience) tested 100 mg L-theanine with 50 mg caffeine in 27 people. The combination improved both speed and accuracy on an attention-switching task at 60 minutes. It also reduced susceptibility to distracting information in a memory task at 60 and 90 minutes.
- Giesbrecht et al. (2010, Nutritional Neuroscience) used 97 mg L-theanine and 40 mg caffeine in 44 young adults. Task-switching accuracy and self-reported alertness improved, and tiredness dropped.
- Camfield et al. (2014, Nutrition Reviews) pooled 11 randomized placebo-controlled human studies in a meta-analysis. It found moderate effect sizes for caffeine plus L-theanine on alertness and attention-switching accuracy in the first two hours after the dose.
What did the combination not do?
Giesbrecht found no significant effect on visual search, choice reaction time, or mental rotation. Haskell found that L-theanine on its own raised "headache" ratings and lowered correct serial-seven subtractions. The gains came from the combination, and only on certain attention tasks.
Camfield also noted that effect size moved more with the caffeine dose than with the L-theanine dose, especially in the first hour. Caffeine does a lot of the work here. L-theanine's contribution is real in these trials but harder to isolate.
What is the right ratio of L-theanine to caffeine?
The trials ran between 1.7 and 2.4 parts L-theanine to one part caffeine. Haskell used 250:150, Owen 100:50, and Giesbrecht 97:40. No trial I found compared ratios head to head, so nobody can say 2:1 beats 1.5:1. So think of 2:1 as roughly what was tested, not a proven best.
Dose table: what each trial used
| Study | Theanine | Caffeine | Ratio |
|---|---|---|---|
| Haskell 2008 | 250 mg | 150 mg | 1.7 : 1 |
| Owen 2008 | 100 mg | 50 mg | 2.0 : 1 |
| Giesbrecht 2010 | 97 mg | 40 mg | 2.4 : 1 |
| Deadline (3 caps) | 200 mg | about 137 mg | 1.5 : 1 |
Ratios are my arithmetic. The Deadline row is its own formula, not tested in these trials. from the doses in each abstract. Camfield's meta-analysis pooled 11 studies, so it has no single dose to list.
How much L-theanine and caffeine should you take?
The studied doses were 97 to 250 mg of L-theanine and 40 to 150 mg of caffeine. If you want to stay inside that range, a quick calculation helps: multiply your caffeine dose by two for a target L-theanine dose. A 100 mg dose of caffeine pairs with about 200 mg of L-theanine.
For total caffeine, the FDA cites 400 mg a day as an amount not generally associated with negative effects in most adults. Sensitivity varies a lot between people, and medications and conditions change it. Count every source, including coffee, tea, energy drinks, and supplements.
How long until it works, and how long does it last?
The trials measured performance between 20 and 90 minutes after dosing. Owen checked at 60 and 90 minutes, and Giesbrecht at 20 and 70 minutes. Camfield's pooled effects cover the first two hours. As far as the abstracts show, none tested a full workday or repeated daily use, so they say nothing about the afternoon.
Does it reduce caffeine jitters?
I can't tell you that from this evidence. None of the four abstracts I read reports a jitters measure. They measured alertness, tiredness, reaction times, and accuracy. Haskell did report lower "headache" and "tired" ratings with the combination. If jitters are your problem, the safer lever is a lower caffeine dose.
Where does Deadline fit in?
The Deadline Focus Pill has 200 mg of L-theanine and about 137 mg of caffeine per 3-capsule serving. That is roughly 1.5:1, a bit under the studied range. Part of the caffeine is zümXR, a time-release form, and the trials above used standard caffeine, so they don't speak to it.
The formula also has citicoline (500 mg), rhodiola (500 mg), methylliberine (75 mg), theacrine (50 mg) and a coffeeberry extract. None of the four sources tested those. It costs $129 one time or $99 on subscription, with a 90-day guarantee. If all you want is caffeine and L-theanine, buy those two separately for less. The table above is enough to do it.
Who should skip it or talk to a doctor first?
The FDA advises pregnant or breastfeeding people, and anyone trying to become pregnant, to ask a health care provider how much caffeine to limit. The same goes for anyone on medications or with a condition that makes caffeine hit harder. The FDA also warns against caffeinated energy drinks for children and teens.
Frequently asked questions
Is L-theanine with caffeine better than caffeine alone?
On some attention tasks, yes. In Haskell's trial the combination improved several measures that caffeine alone did not, including simple reaction time, numeric working memory reaction time, and sentence verification accuracy. On other tasks, such as visual search and mental rotation, Giesbrecht saw no benefit. The effect is task-specific and moderate.
How much L-theanine should I take with 100 mg of caffeine?
About 200 mg, based on the 1.7:1 to 2.4:1 ratios in the trials. No study has confirmed that exact pairing.
Can I take caffeine and L-theanine every day?
The trials tested single doses, so they cannot answer that. The FDA's 400 mg daily caffeine figure covers most healthy adults. Check with your doctor if you take medication.
Does a cup of tea give me enough?
Probably not at the studied doses. The FDA puts green tea at about 37 mg of caffeine per 12 ounces, below the 40 mg low end of the trials, and I did not find a reliable per-cup L-theanine figure in the papers above.
Is this medical advice?
No. Dietary supplements are not evaluated by the FDA to diagnose, treat, cure, or prevent any disease. Nothing here is a treatment claim.
Limits of this evidence
The trials are small, with samples from 27 to 44 people in the individual studies I read. They tested single doses in healthy adults, and findings vary by task. Owen and Giesbrecht were both authored by Unilever researchers, and Unilever sells tea. Take the results as a reasonable starting point. Your own experience may differ.
Sources
- Haskell CF et al. The effects of L-theanine, caffeine and their combination on cognition and mood. Biol Psychol. 2008;77(2):113-22. PMID 18006208
- Owen GN et al. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci. 2008;11(4):193-8. PMID 18681988
- Giesbrecht T et al. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci. 2010;13(6):283-90. PMID 21040626
- Camfield DA et al. Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis. Nutr Rev. 2014;72(8):507-22. PMID 24946991
- FDA. Spilling the Beans: How Much Caffeine is Too Much?
Written by Nick. These statements have not been evaluated by the Food and Drug Administration. Deadline products are not intended to diagnose, treat, cure, or prevent any disease.