Amino AcidsL-Theanine

High-dose L-theanine-caffeine combination improves selective attention in acutely sleep-deprived young adults

A double-blind, placebo-controlled crossover trial found that a combination of 200 mg L-theanine and 160 mg caffeine significantly improved hit rate (P=0.02) and target-distractor discriminability (P=0.047) in a visual selective attention task compared to placebo. The combination also produced a significantly greater pre-post-dose reaction time improvement (38.1 ms, P=0.003) and enhanced P3b ERP amplitudes with reduced latencies.

Last updated: Aug 26, 2026•1 RCTs•📖 Read as article →

Evidence Score

Evidence Score42/100
Human RCT★★☆☆☆
Meta-analysis☆☆☆☆☆
Mechanism★★★★★
Safety★★★★☆
Confidencelow

Study Evidence

Study 1. 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.

observational

Nawarathna GS, Ariyasinghe DI, Dassanayake TL · The British journal of nutrition (2025)

Participants: N/A
Duration: Single dose, acute (50 min post-ingestion)
Intervention: 200 mg L-theanine + 160 mg caffeine combination, single dose
Outcome: Selective attention (hit rate, target-distractor discriminability, reaction time), P3b event-related potential amplitude and latency
Effect Size: N/A
Population: 37 overnight sleep-deprived healthy adults aged 22-30 years (21 men)

Result:

PubMed: 40789769DOI: 10.1017/S0007114525104169

Mechanism Graph

Ingestion of L-theanine-caffeine combination
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Increased neural resource allocation in attentional networks
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Greater and faster P3b ERP component (increased amplitude, reduced latency)
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Improved accuracy and speed of selective attention to traffic scenarios

Limitations

  • ⚠Acute sleep deprivation model may not generalize to chronic sleep loss or non-sleep-deprived populations
  • ⚠Single dose design; long-term effects and optimal dosing regimen unknown

Frequently Asked Questions

What is the recommended dose of L-theanine and caffeine for attention improvement?▼

This study used a single dose of 200 mg L-theanine combined with 160 mg caffeine, but optimal dosing may vary by individual and context.

How long does it take for the L-theanine-caffeine combination to affect attention?▼

In this study, effects were measured 50 minutes after ingestion.

Is this combination effective for non-sleep-deprived individuals?▼

This study only tested acutely sleep-deprived young adults; effects in well-rested individuals were not assessed.

What are the potential side effects of this combination?▼

The abstract does not report side effects; caffeine can cause jitteriness or insomnia in sensitive individuals.

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References

  1. 1.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.." The British journal of nutrition, 2025. PMID: 40789769 DOI: 10.1017/S0007114525104169
Disclaimer: This content is for educational purposes only and is not medical advice. Evidence scores reflect the quality and quantity of available research, not clinical recommendations. Always consult a healthcare professional before starting any supplement or intervention.