The effect of green tea amino acid L-theanine formulation on markers of stress and quality of sleep (THESleep project) - a study protocol for a pilot randomised control trial.
Bulman A, McKune A, et al. • Contemporary clinical trials • 2026
This paper describes a protocol for a pilot randomised controlled trial evaluating the effects of different concentrations of L-theanine functional beverage sachets (100mg, 200mg, 400mg, or placebo) on sleep quality and stress markers in individuals with mild to moderate sleep disturbances over a 14-day intervention period.
Key Findings
Background
L-theanine is commercially applied in functional beverages and supplements for stress and sleep despite a lack of conclusive evidence in the literature.
L-theanine (L-THE) is a non-proteinogenic amino acid predominantly found in the leaves of Camellia sinensis, which produces green, white, oolong, black, aged Pu-erh, and ripened Pu-erh teas.
The paper identifies a gap between commercial use and scientific evidence, noting 'potential nootropic effects' for 'alleviating stress and anxiety and improving sleep quality.'
The study is described as 'the first to comprehensively evaluate the effectiveness (optimal dose) of L-THE at improving sleep quality and stress markers using a suite of objective, subjective, physiological, and biochemical tools.'
Methods
The trial was designed as a randomised, double-blind, placebo-controlled, parallel-group, four-arm, dose-response intervention study.
Sixty healthy participants aged 18–65 with mild to moderate sleep disturbances were recruited.
Participants were randomly allocated in a 1:1:1:1 ratio to one of four arms: 100mg L-THE, 200mg L-THE, 400mg L-THE, or placebo.
The intervention consisted of consuming a functional beverage sachet for 14 days following a 7-day baseline period.
The study was registered with UCHREC Approval Number 2023-13247 and ACTRN12623000776606, with Universal Trial Number U1111-1292-0328.
Methods
The primary outcomes were changes from baseline in objective and subjective sleep quality parameters.
Both objective and subjective sleep quality measures were included as primary outcome measures.
Changes were assessed relative to a 7-day baseline period preceding the 14-day intervention.
The study aimed to determine an optimal concentration of L-theanine for improving sleep quality.
Methods
Secondary outcomes included biochemical, physiological, and subjective stress markers measured relative to baseline.
The study employed 'a suite of objective, subjective, physiological, and biochemical tools' to assess stress markers.
This multi-modal approach is described as a distinguishing feature of the trial design compared to prior research.
Methods
The trial was designed as a pilot study to determine the optimal dose of L-theanine across three active concentrations.
Three active doses were tested: 100mg, 200mg, and 400mg of L-theanine.
The dose-response design was intended to identify an optimal concentration for future research and application.
The pilot nature of the study reflects the authors' acknowledgment of the limited conclusive evidence currently available in the literature.
What This Means
This paper describes the design and protocol of a small clinical trial (called the THESleep project) investigating whether a green tea amino acid called L-theanine can help people who have mild to moderate trouble sleeping. L-theanine is already widely sold in teas, supplements, and functional beverages marketed to reduce stress and improve sleep, but the scientific evidence for these effects is not yet conclusive. To address this gap, the researchers designed a rigorously controlled study where 60 participants were randomly assigned to drink a beverage sachet containing either a placebo, 100mg, 200mg, or 400mg of L-theanine every day for two weeks.
The study measured sleep quality using both objective tools (such as devices that track sleep) and subjective tools (such as questionnaires), as well as biological and physiological markers of stress. The researchers also tracked participants for a week before the intervention began to establish a baseline. By testing three different doses against a placebo, the trial was designed to identify not just whether L-theanine works, but which dose might work best.
This research matters because millions of people worldwide experience sleep disturbances and stress, and many already use L-theanine products without strong scientific backing. This research suggests that a carefully controlled trial using multiple measurement methods and dose comparisons could clarify whether L-theanine is genuinely effective and, if so, at what amount. As a protocol paper, it does not yet report results — those will come when the trial is completed.
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Bulman A, McKune A, Georgousopoulou E, Sergi D, Naumovski N. (2026). The effect of green tea amino acid L-theanine formulation on markers of stress and quality of sleep (THESleep project) - a study protocol for a pilot randomised control trial.. Contemporary clinical trials. https://doi.org/10.1016/j.cct.2026.108306