Supplement analysis backed by scientific evidence · PT

← All supplements
Moderate evidenceBrain & cognition

Caffeine + L-Theanine

The most studied nootropic stack: caffeine supplies the alertness and theanine takes some of the edge off. The attention benefit is real but small, and most of it comes from the caffeine.

Evidence last reviewed: August 2026

View on iHerb Ships to 180+ countries · welcome discount for new customers

What the science says

  • Improved attention and alertness Moderate evidence

    A systematic review and meta-analysis of randomized trials in healthy participants found that theanine combined with caffeine improved attention outcomes more reliably than either compound alone. Effect sizes were small and clearest on simple attention tasks rather than complex reasoning.

  • Helps under sleep deprivation Moderate evidence

    A double-blind crossover trial in acutely sleep-deprived young adults found a high-dose theanine-caffeine combination improved behavioural and electrophysiological measures of selective attention. This is one trial in a specific, stressed population.

  • Signal in ADHD is preliminary Limited evidence

    A proof-of-concept neuroimaging randomized trial in boys with ADHD reported improved sustained attention and inhibitory control with the combination. The sample was small and designed to generate hypotheses, not to guide treatment.

Dosage & safety

Studied doseTypical studied ratios are 50–100 mg caffeine with 100–200 mg L-theanine, taken once. Doses above 200 mg of caffeine bring diminishing returns and more side effects.
SafetyThe caffeine drives the risk: insomnia, anxiety, palpitations and raised blood pressure in sensitive people. Avoid within 8 hours of bedtime and in pregnancy limit total caffeine to 200 mg/day. Theanine itself is well tolerated but may add to the effect of blood-pressure-lowering drugs.

Scientific references

Where to buy

View on iHerb

Ships to 180+ countries · welcome discount for new customers

Referral link — this site may earn a commission on purchases.

Related in Brain & cognition