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.
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
Glycine and sleep quality
Moderate3 g of glycine before bed improves subjective sleep quality and reduces daytime sleepiness and fatigue in controlled trials.
Glycine and collagen synthesis
ModerateGlycine supplementation increases collagen synthesis markers, supporting joint and skin health.
How it connects
Relationships between Glycine and other supplements in the matrix.
A classic sleep stack: glycine lowers core body temperature while magnesium glycinate 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 pairingBoth are conditionally essential under stress and support gut and immune function through complementary pathways.
Compare the pairingGlycine is one of the three amino acids the body uses to synthesise creatine endogenously.
Compare the pairingImportant cautions
- Very high doses may theoretically interfere with serine metabolism long-term.
More Amino Acids
Creatine
The most-studied performance and cognition supplement.
L-Arginine
The nitric oxide precursor for blood flow and cardiovascular health.
L-Citrulline
A superior nitric oxide booster that outperforms arginine for pumps and endurance.