L-theanine and GABA: what the evidence says

L-theanine

L-theanine is an amino acid found in tea leaves, and part of why tea feels different from coffee. It is associated with relaxed alertness rather than drowsiness.

A 2025 meta-analysis of 18 randomised trials found small but significant improvements in how quickly people felt they fell asleep, in daytime functioning and in overall self-rated sleep quality.¹ The authors noted that few trials tested L-theanine on its own, so some of the effect may come from what it was combined with.

In a four-week trial of 30 healthy adults, 200 mg a day reduced stress-related symptoms and improved sleep-quality scores compared with placebo.² It is one small trial, and two of its authors worked for the company that supplied the L-theanine.

GABA

GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter in the brain: the system that quiets excess signalling. The question is whether GABA swallowed as a supplement does anything to that system.

It has long been thought that GABA does not cross the blood-brain barrier, and the studies are contradictory. A 2015 review concluded that the mechanism is far from clear, that it might act through the gut's own nervous system instead, and that much of the positive evidence came from researchers with potential conflicts of interest.³ A 2020 systematic review of 14 trials found limited evidence for stress and very limited evidence for sleep.⁴

Why they are paired

They aim at the same moment from different directions: L-theanine for calm without sedation, GABA for the brain's own quieting system. That pairing is common in evening formulas, including ours. We would rather tell you which half has the stronger evidence than pretend both are equal.

Where this fits for athletes

The usual obstacle after an evening session or a night game is not a lack of tiredness. It is a nervous system that stays switched on. Sleep in elite athletes is often short and poor in quality, with training, competition and stress among the drivers.⁵ An ingredient that supports calm without sedation suits that window, and the rest of the evening is in What to drink in the evening after training.

In practice

• Timing. Evening, or before a stressful window, since the aim is to settle rather than stimulate.
• Not a fix for the basics. Neither will undo too little sleep or too much late caffeine.
• Pair with the foundations. Magnesium if your intake is low, and a regular bedtime.

A note on the studies above: they tested set amounts of a single ingredient over weeks. A shot is not a study protocol, and we do not claim that SOLACE or CALM reproduces these results.