Caffeine + L-Theanine: Benefits, Dosage & Research

Caffeine and L-theanine have been studied together for attention and focus. Some results are promising, but they do not establish a universal ratio or guaranteed relief from caffeine side effects. Caffeine's exercise evidence is stronger than evidence for added training benefits from the pairing.12

  • Caffeine and exercise research
  • Human attention studies
  • Studied amounts and ratios
  • Safety and individual response
See the research View the 4 Gauge formula

By Connor Southworth, owner of 4 Gauge.

Disclosure: Connor Southworth owns 4 Gauge, which sells pre-workout and other sports supplements. This page discusses ingredient research and the current product label.

Research checked:

Three 4 Gauge pre-workout containers
150 mgCAFFEINE
200 mgL-THEANINE
8HUMAN STUDIES & EVIDENCE REVIEWS
On this page
  1. What Are They?
  2. How Do They Work?
  3. What the Evidence Supports
  4. Caffeine
  5. L-Theanine Alone
  6. What Human Studies Tested
  7. Studied Amounts & Ratios
  8. Safety
  9. In 4 Gauge
  10. FAQ
  11. Sources
The Basics

What are caffeine and L-theanine?

Caffeine is a stimulant. L-theanine is an amino acid found in tea and is not itself a stimulant.

They are sometimes combined in supplements, but each ingredient—and the combination—needs to be evaluated for the specific outcome being claimed.

For definitions and related label terms, see the caffeine and L-theanine entries in our pre-workout ingredient glossary.

Mechanism

How do caffeine and L-theanine work?

Caffeine mainly acts by blocking adenosine receptors, helping reduce perceived fatigue and sleepiness.1

L-theanine research explores effects on attention, stress responses, and brain activity. These findings do not establish that it removes caffeine from the body or consistently neutralizes caffeine's effects.23

Keep in mind

A plausible explanation for combining ingredients is a starting point for research. The useful question is what happened in controlled human studies.

Evidence At A Glance

What does the evidence support?

Different questions have very different amounts of evidence behind them. Each card says what was studied and what to keep in mind.

Substantial research

Caffeine and exercise

Response varies by person and activity.1

Caffeine evidence →
Some laboratory tasks

The combination and attention

Findings depend on the task and the comparator.24

Study table →
A different question

L-theanine alone

Research on cognition and stress-related outcomes. Acute and repeated-use studies answer different questions.23

L-theanine evidence →
Small, mixed trials

Added athletic benefits

Findings do not consistently show superiority to caffeine alone.678

Athlete studies →
Not established

An optimum ratio

Different protocols have been tested. A tested ratio is not a universal optimum.

Amounts & ratios →
A separate question

Finished-product effects

Ingredient findings do not validate every commercial formula.

In 4 Gauge →
Ingredient · 01
Caffeine

Caffeine: the stronger exercise evidence

Exercise research, studied amounts, and individual response

Caffeine can improve several aspects of exercise performance, although it does not help every person or every task. Many trials use 3–6 mg/kg of body weight, and some find benefits with lower amounts. Taking more can increase unwanted effects without reliably improving performance.1

Study amounts are context

Those study amounts are context, not a personal target. Our guide to how much caffeine is in pre-workout explains total intake, sensitivity, and practical comparisons.

Ingredient · 02
L-Theanine

L-theanine alone: a different research question

Repeated daily use is not the same as one pre-workout serving

Research on theanine alone should be kept separate from research on the combination.

One small trial studied 200 mg daily for four weeks. Several stress-related and sleep scores improved from baseline, but only some sleep measures improved relative to placebo. That does not establish that a single pre-workout serving prevents anxiety or protects sleep after caffeine.3

The Combination

Caffeine + L-theanine: what human studies tested

The table below separates the participants, amounts, outcomes, and limits. These protocols are research examples, not instructions to reproduce the doses.

Human studies of caffeine and L-theanine: participants, amounts, outcomes, comparators, and limitations
Study Participants / design Caffeine and L-theanine amounts Task or outcome Result and comparator Main limitation
Payne et al., 20252 Systematic review and meta-analysis of randomized trials in healthy participants; literature searched through August 2023. Varied across studies. Cognition, mood, and sleep. Some attention outcomes favored the combination over placebo. Pooled effects on alertness and mood were not statistically significant. Different tasks and protocols; many included trials were rated at high risk of bias. Not a finished-product or universal-ratio test.
Giesbrecht et al., 20104 44 young adults; placebo-controlled trial. 40 mg caffeine + 97 mg L-theanine. Attention tasks and subjective alertness. Improved task-switching accuracy and self-rated alertness, and lower self-rated tiredness, versus placebo. No significant effect on the other tasks. The reported placebo comparisons do not establish superiority to caffeine alone.
Dodd et al., 20155 24 healthy adults; crossover trial with caffeine-alone, L-theanine-alone, combination, and placebo conditions. 75 mg caffeine + 50 mg L-theanine. Attention, mood, and cerebral blood flow. The combination did not provide a positive behavioral effect at the tested amounts; caffeine-alone benefits were not retained. One specific protocol; does not settle all combinations.
Yilmaz et al., 20236 22 elite curling athletes; crossover trial with caffeine-alone, L-theanine-alone, combination, and placebo conditions. 6 mg/kg caffeine + 6 mg/kg L-theanine. Curling shots and Stroop testing. Combined intake improved guard, draw, and take-out shot performance versus placebo. Small specialist sample; high body-weight-based amounts; not ordinary gym training.
Razazan et al., 20257 12 male wrestlers; crossover trial with caffeine-alone, L-theanine-alone, combination, and placebo conditions. 3 mg/kg caffeine + 3 mg/kg L-theanine. Physical tests, wrestling-specific fitness, cognition, and reported symptoms. Several outcomes favored the combination versus placebo. Fewer outcomes differed from caffeine alone. Small sample; participant ages and some statistics differ between the abstract and the full results. Not a finished-formula or cardiovascular safety trial.
Tuncer et al., 20268 20 competitive athletes (12 men, 8 women); crossover trial. 3 mg/kg caffeine + 200 mg L-theanine. Isometric strength, intermittent endurance, and hand-eye coordination. No added strength benefit from the combination; no significant condition differences in endurance, grip strength, or coordination. L-theanine alone lowered leg strength versus caffeine and placebo, and back strength versus placebo. Small study with specific tests; null findings do not establish universal ineffectiveness.
Hidese et al., 20193 30 adults; four-week crossover trial. No caffeine intervention; 200 mg/day L-theanine. Stress-related symptoms, sleep, and cognition. Several scores improved from baseline; selected sleep subscales improved relative to placebo. Repeated L-theanine-alone use, not an acute caffeine-pairing test.

Scroll the table sideways to see every column.

What the athlete studies mean for training

The athlete findings are worth investigating, but they do not consistently show that adding theanine improves exercise performance beyond caffeine alone. Different sports and protocols can produce different results.678

The wrestler paper also reports conflicting participant ages between its abstract and methods. That limits confident interpretation of who its findings represent.7

The appropriate conclusion

Added athletic benefits remain uncertain—not that the pairing always works or never works.

Studied Amounts & Ratios

Is there a best caffeine-to-L-theanine ratio?

The studies above do not establish a universal optimum.

A ratio describes relative quantities. It does not identify an effective or safe dose by itself.

Ratio arithmetic examples (not dose recommendations)
ExampleCaffeineL-theanineTheanine:caffeine ratioMeaning
Arithmetic example 100 mg 100 mg 1:1 Equal quantities; not a recommendation.
Arithmetic example 100 mg 200 mg 2:1 Twice as much theanine; not proof of greater calming.
Current 4 Gauge serving 150 mg 200 mg 4:3, approximately 1.33:1 A label description, not an established optimum.

Amount and ratio both matter. A 1:1 pairing could mean 50 mg of each ingredient or 400 mg of each.

For a hypothetical 70 kg participant, the wrestler protocol's 3 mg/kg means 210 mg of each ingredient. The curling protocol's 6 mg/kg means 420 mg of each. These are calculations explaining research protocols—not suggested intakes.67

Neither is the same as 150 mg caffeine plus 200 mg L-theanine.

See our pre-workout ingredient dosage guide for additional context on amounts, forms, and timing.

Safety

Safety: caffeine still matters

The FDA identifies 400 mg of caffeine per day as an amount not generally associated with negative effects for most adults. That is not a target, and individual sensitivity varies. Count caffeine from all sources, including drinks, supplements, and relevant medications.9

EFSA notes that even 100 mg close to bedtime can affect sleep in some adults. Theanine should not be treated as protection against late caffeine use.10

If caffeine makes you feel unwell, do not increase theanine to push through the symptoms. Reduce or avoid further caffeine and seek appropriate medical advice.

People who are pregnant, trying to become pregnant, breastfeeding, taking medication, or managing a medical condition should discuss caffeine and supplement use with a healthcare professional. Adult research does not establish suitability for children or teenagers.9

Avoid pure or highly concentrated caffeine products. Small measuring errors can be dangerous.11

For practical symptom guidance, see pre-workout side effects: causes and what to do.

In The Formula

Caffeine + L-theanine in 4 Gauge

A current full serving of 4 Gauge contains 150 mg caffeine anhydrous and 200 mg L-theanine.12

We chose a measured caffeine amount and disclose both ingredients so you can compare the formula with the research and your own needs.

These label facts do not establish guaranteed freedom from jitters, anxiety, sleep disruption, or a post-workout energy drop.

The studies discussed here tested ingredients or specific experimental interventions. They should not be presented as clinical validation of the finished 4 Gauge formula.

If you prefer a formula with these disclosed amounts, view 4 Gauge's current ingredients and serving information.

Know what's in your serving

Compare the disclosed ingredients, serving directions, and caffeine amount with your needs before choosing a pre-workout.

  • Disclosed caffeine amount
  • Disclosed L-theanine amount
  • Fully disclosed formula
  • Current serving information
View the formula & shop 4 Gauge
Explore the Research Hub →
FAQ

Frequently asked questions

What does L-theanine do when taken with caffeine?

Some controlled studies found improvements in attention-related tasks. Results depend on the amounts, task, and comparator; theanine should not be treated as a guaranteed caffeine-side-effect remedy.45

What is the best caffeine-to-L-theanine ratio?

No universal optimum is established. Compare actual quantities and study outcomes rather than choosing solely by a ratio.

Does L-theanine always preserve caffeine's benefits?

No. Some positive findings exist, but one cognitive trial did not retain caffeine-alone benefits when theanine was added.5

Does the combination improve workout performance?

Small athlete studies have produced mixed results. The evidence does not consistently establish added exercise benefits beyond caffeine alone.678

Will L-theanine prevent a caffeine crash?

The research summarized here does not establish reliable prevention of a post-caffeine energy drop. Do not interpret an attention-task improvement as proof of crash prevention.

Can I take the combination every day?

This page does not establish a universal daily regimen. Follow the product label, monitor total caffeine and symptoms, and consider medical circumstances with a clinician.9

How much caffeine and L-theanine are in 4 Gauge?

The current full serving lists 150 mg caffeine anhydrous and 200 mg L-theanine. Check the current label and serving directions before use.12

Continue Your Research

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About the Author

Who wrote this page

Connor Southworth, owner of 4 Gauge
Author

Connor Southworth

Owner of 4 Gauge

Connor Southworth owns 4 Gauge and works on its product development and ingredient selection. This page is a brand-owned educational resource. It has not been independently or medically reviewed.

June 25, 2026First published
October 13, 2026Research checked
Sources

Sources and references

Each source is labelled by type: position stand, systematic review, human trial, official guidance, or brand information. Not every source is a clinical trial.

01 · Reviews & position standsCaffeine, L-theanine, and the combination

  1. 1.Position standGuest NS, et al. International Society of Sports Nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr. 2021. PubMed · Full text
  2. 2.Systematic review & meta-analysisPayne ER, et al. 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. PubMed · DOI · Full text. Disclosure: the lead author’s PhD studentship is funded by Lipton Teas and Infusions; coauthor Joy Dubost is employed by Lipton Teas and Infusions, and coauthor Arno Greyling is employed by Unilever.

02 · Human trialsL-theanine alone

  1. 3.Randomized trialHidese S, et al. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients. 2019. PubMed · Full text

03 · Human trialsCaffeine + L-theanine

  1. 4.Randomized trialGiesbrecht T, et al. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutritional Neuroscience. 2010. PubMed
  2. 5.Randomized trialDodd FL, et al. 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. Psychopharmacology. 2015. Publisher · Full text
  3. 6.Randomized trialYilmaz U, et al. Effect of single or combined caffeine and L-theanine supplementation on shooting and cognitive performance in elite curling athletes: a double-blind, placebo-controlled study. J Int Soc Sports Nutr. 2023. PubMed · Full text
  4. 7.Randomized trialRazazan R, et al. Performance-enhancing effects of caffeine and L-theanine among Iranian elite wrestlers: a focus on cognitive and specific physical performance. J Int Soc Sports Nutr. 2025. PubMed · Full text
  5. 8.Randomized trialTuncer SY, et al. Acute effects of combined and isolated caffeine and theanine supplementation on physical and cognitive performance in competitive athletes: a randomized, double-blind, placebo-controlled crossover study. Frontiers in Nutrition. Published January 26, 2026. Full text · PubMed

04 · Official guidanceCaffeine safety

  1. 9.Official guidanceU.S. Food and Drug Administration. Spilling the Beans: How Much Caffeine Is Too Much? FDA
  2. 10.Official guidanceEuropean Food Safety Authority. Caffeine. EFSA
  3. 11.Official guidanceU.S. Food and Drug Administration. FDA Warns Consumers About Pure and Highly Concentrated Caffeine. FDA

05 · Brand informationProduct label

  1. 12.Brand information4 Gauge Pre-Workout current product page. Brand-owned product information; not independent effectiveness evidence. 4 Gauge

This article is for educational purposes only and is not a substitute for medical advice. These statements have not been evaluated by the Food and Drug Administration. 4 Gauge products are not intended to diagnose, treat, cure or prevent any disease. Consult a qualified clinician before starting any supplement, especially if you are pregnant, sensitive to stimulants, have a medical condition or take medication. © 2026 4 Gauge.