Glycine
Also known as L-Glycine
Glycine is the simplest amino acid and one of the most abundant in the body. It acts as an inhibitory neurotransmitter in the brainstem and spinal cord, contributes to collagen and glutathione synthesis, and plays a significant role in detoxification. Its standout clinical evidence is for improving sleep quality even at low doses (3 g before bed).
Benefits
Improves sleep quality
Moderate3 g of glycine before bed consistently improves subjective sleep quality, reduces next-day fatigue, and may lower core body temperature to promote sleep onset.
Supports collagen synthesis
ModerateGlycine is the most abundant amino acid in collagen. Supplementation provides substrate that is often limiting in modern diets (which discard collagen-rich cuts).
Glutathione precursor
ModerateTogether with cysteine and glutamate, glycine is a building block of glutathione, the body's primary antioxidant and detoxification molecule.
Metabolic and blood-sugar benefits
PreliminarySome evidence suggests glycine improves insulin sensitivity and metabolic markers, possibly by improving glucagon response.
May help buffer overmethylation
PreliminaryGlycine can accept methyl groups via glycine N-methyltransferase, producing sarcosine. Some clinicians report it helps people who feel overstimulated or wired from too much methylation support.
Pros & cons
Pros
- Very safe, one of the most benign supplements available
- Cheap and widely available
- Noticeable sleep improvement at just 3 g
- Mildly sweet taste, easy to add to drinks
Cons
- Sleep benefit is modest rather than dramatic
- Collagen benefits require consistent long-term intake
Side effects
Soft stools at high doses
Very high doses (>10 g) can cause loose stools due to osmotic effects.
How to take it
Typical dose
3 g before bed for sleep; up to 10 g/day for collagen support
Timing
30–60 minutes before bed for sleep; with meals for collagen/metabolic goals
Common forms
Tip: Powder dissolved in water is the most practical form. The mildly sweet taste makes it easy to drink.
What the research says
[1]Glycine and sleep quality
Moderate3 g of glycine before bed improves subjective sleep quality and reduces daytime sleepiness and fatigue in controlled trials.
Reviews of controlled trials · 2012PubMed[2]Glycine and collagen synthesis
ModerateGlycine supplementation increases collagen synthesis markers, supporting joint and skin health.
Collagen research · 2019PubMed
How Glycine interacts
Synergies, absorption effects, and cautions between Glycine and other supplements in the matrix.
Glycine and its direct connections · click a node to open its guide
A sleep pairing with a built-in shortcut: magnesium glycinate is magnesium bound to glycine, so that form already delivers both. A standalone 3 g dose before bed (the amount sleep studies used) tops up the glycine, lowering core body temperature while magnesium relaxes muscles and calms the nervous system.
Compare the pairingNAC provides cysteine while glycine provides another rate-limiting precursor; together they are more effective at raising glutathione than either alone (GlyNAC protocol).
Compare the pairingGlycine (inhibitory) and tryptophan-derived serotonin/melatonin work through complementary pathways to support sleep.
Compare the pairingStructurally glycine plus three methyl groups, but functionally distinct: TMG donates methyls (becoming dimethylglycine) while glycine can accept them, together they help buffer methylation balance.
Compare the pairingBoth are conditionally essential under stress and support gut and immune function through complementary pathways.
Compare the pairingGlycine makes up about a third of collagen, so supplementing it provides raw material that collagen synthesis depends on.
Compare the pairingGlycine is one of the three amino acids the body uses to synthesise creatine endogenously.
Compare the pairingGlycine lowers core body temperature, a physiological trigger for sleep onset, which complements melatonin's circadian signal.
Compare the pairingFrequently asked questions
What is Glycine used for?
Glycine is most commonly used for sleep, joint health, and stress. 3 g of glycine before bed consistently improves subjective sleep quality, reduces next-day fatigue, and may lower core body temperature to promote sleep onset.
How much Glycine should I take?
A typical dose is 3 g before bed for sleep; up to 10 g/day for collagen support. Powder dissolved in water is the most practical form. The mildly sweet taste makes it easy to drink. Start at the lower end and confirm the right dose for you with a healthcare professional.
When is the best time to take Glycine?
Recommended timing: 30–60 minutes before bed for sleep; with meals for collagen/metabolic goals.
What are the side effects of Glycine?
Reported side effects include soft stools at high doses. Very high doses (>10 g) can cause loose stools due to osmotic effects.
Who should be careful with Glycine?
Very high doses may theoretically interfere with serine metabolism long-term. Speak with a healthcare professional if any of these apply to you.
Important cautions
- Very high doses may theoretically interfere with serine metabolism long-term.
More Amino Acids
5-HTP
A direct serotonin precursor for mood and sleep, use with care.
Collagen
The structural protein for skin, joints, and connective tissue.
Creatine
The most-studied performance and cognition supplement.
Compare Glycine with
Weighing your options? See how Glycine stacks up against similar supplements.
Supports these foundations
Glycine can help reinforce these lifestyle foundations, but it works best on top of them, not in place of them.