A systematic review of randomised controlled trials reveals three critical insights about L-theanine’s effects on sleep. First, the supplement selectively improves sleep quality—accelerating sleep onset and enhancing continuity—without paradoxically increasing total sleep time, making it useful for individuals struggling with sleep efficiency rather than duration.
Second, safety data strongly supports its use: doses up to 900 mg daily produced no next-day drowsiness, cognitive impairment, or motor deficits across all studied populations aged 9–57 years, contrasting sharply with conventional sedating medications. This non-sedating profile is particularly valuable for patients requiring daytime alertness.
Third, L-theanine operates through distinct neurochemical pathways, enhancing GABA and acetylcholine whilst promoting alpha-wave activity. These mechanisms explain its efficacy in counteracting caffeine-induced sleep disruption and creating a relaxed pre-sleep state without pharmacological sedation. The evidence supports 200–450 mg daily as the therapeutic range for sleep optimisation.
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