Supplement analysis backed by scientific evidence · PT

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Moderate evidenceSleep & relaxation

L-Theanine

L-theanine produces small, genuine reductions in acute stress and anxiety and pairs well with caffeine for attention, but individual effects are modest and the sleep evidence is weaker than the marketing suggests.

What the science says

  • Small reduction in acute stress and anxiety Moderate evidence

    A 2026 systematic review and meta-analysis of 31 randomized trials found L-theanine produced small but statistically detectable improvements in affective outcomes, most consistently for acute stress and state anxiety at 200-400 mg. Effects on chronic or clinical anxiety were much less convincing, and the trials are small and heterogeneous.

  • Improves attention when combined with caffeine Moderate evidence

    Meta-analysed RCTs of tea constituents show the combination of roughly 100 mg L-theanine with 40-100 mg caffeine improves attention-switching and reduces distractibility more than either alone in the first 1-2 hours. Taken by itself, theanine's effect on cognitive performance in healthy adults is close to nil.

  • Sleep effects are modest and mostly subjective Limited evidence

    Systematic reviews of theanine sleep trials find small improvements in self-reported sleep quality and refreshed feeling at 200-400 mg before bed, with little consistent change in objective measures such as sleep latency or total sleep time. Theanine is not a sedative and does not behave like one in polysomnography.

Dosage & safety

Studied dose100-400 mg/day. Acute stress and cognition trials used 200-400 mg taken 30-60 minutes before the task, often with 40-100 mg caffeine; sleep trials typically used 200 mg about an hour before bed for 4-8 weeks.
SafetyOne of the better-tolerated supplements; adverse events in trials are rare and mild (headache, drowsiness, GI upset). It may modestly lower blood pressure, so caution with antihypertensives. Because it reduces subjective stimulation, it can blunt the alerting effect of caffeine, which is either the point or an annoyance depending on your goal. No established interactions with sedatives, but combining with alcohol or benzodiazepines has not been well studied. Long-term safety beyond a few months is largely untested.

Scientific references

Where to buy

Nutricost, L-Theanine, 200 mg, 120 Capsules

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