Did you know that glycine can both calm and activate the nervous system? It might sound contradictory, but this amino acid actually has two very different functions in the body’s nerve signals. How does it work, and what determines the effect glycine has?
Glycine is an amino acid that the body can both produce itself and get from food. It’s needed, among other things, to make proteins, collagen, and the antioxidant glutathione—but it also has a less well-known role: glycine acts as a neurotransmitter in the nervous system. This means it affects how nerve cells communicate with each other.
Depending on which receptor glycine binds to, it can either brake the activity of nerve cells or help other signals to be be activated. And this affects everything from movements and reflexes to how the brain processes information.
The nervous system needs both brakes and gas
When we talk about regulating the nervous system, we often mean the body’s ability to wind down after stress. But the nervous system also needs to be able to brake individual signals so that your movements, reflexes, and senses work properly.
Imagine reaching for a glass of water. To make the movement smooth and controlled, certain muscles need to be activated while the activity of other muscles is dampened.
Glycine helps with this braking signal, especially in the spinal cord and brainstem. But in the brain, glycine also has another role. There, it works together with the neurotransmitter glutamate at so-called NMDA receptors, which are important for communication between nerve cells and the brain’s plasticity (its ability to create new connections between nerve cells when you learn something new).
So the same amino acid can both dampen and enable nerve signals. The effect glycine has depends on which receptors it encounters and how the nervous system regulates glycine availability.
How can glycine make a difference to sleep?
Have you slept through the night but still woken up feeling tired? This is exactly the experience researchers have studied when looking at glycine.
In a Japanese study, eleven adults who reported sleep problems took 3 grams of glycine before bedtime. Participants reported improved sleep quality, and sleep monitoring showed, among other things, that they fell asleep faster. The researchers also observed improvements in some tests of memory and attention the following day.
But how can glycine affect sleep?
One possible explanation is body temperature. For us to fall asleep, our core body temperature normally needs to drop slightly. Experimental research has shown that glycine can affect temperature regulation through signaling in the brain, which may help the body transition into sleep more easily.
Interestingly, NMDA receptors also seem to be involved in this process. Although they help activate nerve signals, they can also also be involved in neural pathways that regulate the body’s temperature. An activating signal in the brain can therefore contribute to a process that makes it easier to fall asleep. Researchers have observed this in animal studies, but exactly how it works in humans is not yet clear.
Can glycine help the brain stay sharp?
And the connection to sleep leads us to something else: how the brain functions the next day.
In a 2012 study, people who were allowed to sleep for several nights less than usual. Those who took glycine before bedtime reported less fatigue and showed improvements in some tests of attention and reaction time compared with those who received a placebo instead of glycine.
But there’s an important difference between this and claiming that glycine generally improves memory. The results primarily concern how we and our brains function when we don’t get quite enough sleep.
At the same time, as we mentioned earlier, glycine is involved in NMDA signaling, which plays a central role in the brain’s plasticity, learning, and memory formation. This is one reason researchers are also studying glycine and related substances in connection with cognitive function and neurological diseases.
Research is still at an exploratory stage, but shows that glycine’s importance for the brain goes beyond its effects on sleep and muscle control.
And what about glycine and mood?
In integrative health and naturopathy, glycine is also discussed in connection with anxiety, irritability, and mood swings, particularly during periods of hormonal changes such as perimenopause and menopause.
Why is that? Glycine is involved in inhibitory signaling in the nervous system, while NMDA receptors are part of the neural networks that influence emotions, behavior, and cognition.
Researchers have also studied glycine in psychiatric conditions such as schizophrenia, where NMDA signaling may be altered. Some studies have shown improvements in symptoms, while others have yielded more mixed results.
However, we still know little about how glycine supplements affect anxiety, irritability, or mood swings in otherwise healthy people.
When might taking a glycine supplement be appropriate?
Glycine occurs naturally in foods such as meat, fish, legumes, and collagen-rich foods. The body also produces glycine itself, but nutrition researchers have long debated whether the body's own production always meets all its needs.
When it comes to supplements, sleep is the area where we have some of the clearest results in healthy adults. Several smaller studies have investigated 3 grams of glycine before bedtime and reported positive effects on perceived sleep quality, morning fatigue, and some measures of mental performance.
Glycine is also part of magnesium bisglycinate, in which magnesium is bound to the amino acid glycine. In a randomized study from 2025, 155 adults received either magnesium bisglycinate or a placebo for four weeks. The magnesium group reported a small but measurable improvement in sleep problems compared with the placebo group. However, the study could not determine how much of the effect was due to magnesium and how much was due to glycine.
One important thing to know is that the body carefully regulates glycine levels, including through transport proteins that control its availability around nerve cells. So we cannot determine which receptors are affected simply by consuming more glycine.
However, it is clear that glycine has many interesting and important effects in the body - effects that researchers are still trying to fully understand.
Sources
Schmidt & Thompson (2016). Glycinergic signaling in the human nervous system, PubMed Central
Yamadera et al. (2007). Glycine ingestion improves subjective sleep quality in human volunteers, Wiley Online Library
Bannai et al. (2012). The Effects of Glycine on Subjective Daytime Performance in Partially Sleep-Restricted Healthy Volunteers, DOI
Kawai et al. (2015). The Sleep-Promoting and Hypothermic Effects of Glycine are Mediated by NMDA Receptors in the Suprachiasmatic Nucleus, Neuropsychopharmacology
Soh et al. (2024). The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review, PubMed Central
Schuster, J., Cycelskij, I., Lopresti, A. & Hahn, A. (2025). Magnesium Bisglycinate Supplementation in Healthy Adults Reporting Poor Sleep (2025), PubMed Central
Jennifer Harrington (2024). Glycine: A Powerful Amino Acid for Midlife Women's Health, Menopause Natural Solutions, published January 21, 2024.
