Lowers core body temperature slightly - the exact physiological signal your brain uses to initiate deep sleep.

Glycine is a simple amino acid that acts as an inhibitory neurotransmitter, helping the body ease into deep sleep without disrupting its natural sleep architecture. It works at glycine receptors in the brainstem and spinal cord, producing a calming inhibitory tone that gently lowers core body temperature through vasodilation — a well-established thermoregulatory signal for sleep onset.

By shifting the body toward parasympathetic ("rest and restore") dominance and quieting sympathetic activity, glycine smooths the transition from wakefulness into non-REM sleep. It also reaches the hypothalamic–preoptic region and accumulates in the pineal gland, supporting melatonin synthesis and reinforcing circadian rhythm.

Importantly, glycine preserves REM and slow-wave sleep while shortening the time it takes to reach deeper stages. Clinically, this shows up as better sleep efficiency, easier sleep onset, and higher satisfaction with sleep quality — particularly in people with poor baseline sleep.

https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2012.00061/full

https://link.springer.com/article/10.1111/j.1479-8425.2006.00193.x

https://link.springer.com/article/10.1111/j.1479-8425.2007.00262.x