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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.

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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.

How to take it

TimingTake it in the morning or early afternoon, and never within 8 hours of bedtime.
With food?Food makes little difference; take it with a snack if caffeine upsets your stomach.
Worth knowingIf caffeine already makes you jittery, keep the ratio at roughly 2:1 theanine to caffeine — that is what the calming effect in the trials rests on.

Interactions

With medications

  • fluvoxamine and ciprofloxacin

    Both block CYP1A2 and slow caffeine clearance, so a normal dose feels far stronger and lasts much longer. Cut the caffeine dose substantially or avoid it while taking these drugs

  • stimulant medication such as ADHD drugs

    Additive anxiety, palpitations and raised blood pressure. Reduce or skip added caffeine on medication days

  • blood pressure medication

    Caffeine raises blood pressure acutely, while theanine may lower it slightly — the net effect is unpredictable. Monitor your blood pressure when starting

With other supplements

  • other caffeine-containing supplements or pre-workouts

    Doses stack quickly past the point of diminishing returns. Add up total daily caffeine from all sources

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does caffeine and L-theanine improve focus?

Caffeine plus L-theanine has moderate evidence for attention: a meta-analysis of randomized trials in healthy people found the combination improved attention more reliably than either alone. The effect is small, clearest on simple attention tasks, and most of it comes from the caffeine.

What is the best caffeine to L-theanine ratio?

Studies of caffeine and L-theanine typically used 50–100 mg caffeine with 100–200 mg L-theanine, taken once. If caffeine makes you jittery, keep roughly a 2:1 ratio of theanine to caffeine; caffeine above 200 mg brings diminishing returns and more side effects.

When should I take caffeine and L-theanine?

Take caffeine plus L-theanine in the morning or early afternoon, and never within 8 hours of bedtime. Food makes little difference, though a snack helps if caffeine upsets your stomach.

Does caffeine and L-theanine help ADHD?

The evidence for caffeine plus L-theanine in ADHD is limited to a small proof-of-concept neuroimaging trial in boys that reported better sustained attention and inhibitory control. It was designed to generate hypotheses, not guide treatment, and stimulant ADHD drugs add to caffeine's anxiety and palpitations.

Scientific references

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