A systematic review of 13 randomised controlled trials involving 550 participants has established a clear dosing recommendation for L-theanine supplementation. The optimal daily dose of 200–450 mg consistently improved sleep latency, continuity, and overall sleep efficiency without producing next-day cognitive or motor impairment.
Interestingly, the review found that even higher doses—up to 900 mg daily administered over 8 weeks—did not trigger clinically relevant drowsiness or sedation, suggesting a wide safety margin. This dose-response finding is particularly significant for clinical practitioners considering L-theanine as an alternative to conventional sleep medications.
The mechanism involves enhancement of inhibitory neurotransmitters and increased alpha-wave activity in the brain, creating conditions conducive to sleep onset. Whilst the evidence base is strongest in healthy and subclinical populations, these findings position L-theanine as a well-tolerated option for sleep optimisation without the daytime impairment associated with traditional hypnotics.
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