3 g before bed (sleep). In metabolic studies, 5–15 g/day.
3 g before bed improves sleep quality and the feeling of being rested the next day.
View the study (clinical trial) →May slightly improve markers such as insulin sensitivity.
View the study (review) →3 g before bed: through NMDA modulation and a drop in core body temperature, it could reduce anxious awakenings and nighttime palpitations. Direct clinical evidence is limited, but the anxiolytic profile is coherent.
Glycine antagonizes glutamate in the fear circuit. Sarcosine (N-methylglycine) showed an effect in OCD/panic as an adjunct to SSRIs. Extrapolation to glycine is reasonable but without a direct RCT.
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Glycine is the smallest and structurally simplest amino acid in the body, but that apparent chemical humility conceals a surprisingly broad functional profile: it is the second most important inhibitory neurotransmitter of the central nervous system (after GABA), it is one of the three components of glutathione (the main endogenous antioxidant), it is the most abundant amino acid in collagen (one third of all residues), and it takes part in the synthesis of creatine, hemoglobin, and bile acids.
Although the body synthesizes glycine endogenously from other amino acids, modern calculations suggest that this production does not meet the adult's real needs (especially for collagen synthesis), which has led some researchers to reclassify it as a "conditionally essential" amino acid; supplementation with modest doses (3-15 g/day) compensates for this functional deficit and has been associated with benefits for sleep, cognition, and metabolic biomarkers.
The indication with the best clinical evidence is improved sleep: several Japanese randomized trials have shown that 3 grams of glycine taken 30-60 minutes before bedtime reduce sleep latency, improve the subjective quality of rest, and reduce the feeling of morning fatigue, especially in people with insufficient or poor-quality sleep due to stress.
The most plausible mechanism combines glycine's inhibitory activity on the central nervous system (similar to GABA but gentler) with a peripheral vasodilatory effect that increases the release of body heat and facilitates the drop in core temperature that normally precedes sleep onset; this temperature decline is one of the most important physiological triggers of deep sleep, and facilitating it explains a good part of the subjective effect reported by users.
As an indirect consequence of improving nighttime sleep quality, glycine supplementation is associated with improvements in processing speed, attention, and subjective well-being the following day, especially in people who are sleep-deprived or have nonrestorative sleep; these effects are consistent across the available trials and are noticeable from the first weeks of continued use.
As the main amino acid of collagen, glycine is necessary for the synthesis of any connective tissue: articular cartilage, tendons, ligaments, skin, blood vessels, bones; supplementation with glycine alone (10-15 g/day) or combined with other collagen precursors (vitamin C, proline, lysine) facilitates collagen synthesis and may contribute to recovery from tendinopathies, to joint health in osteoarthritis, and to skin quality in aging.
Several small studies have shown that glycine improves peripheral insulin sensitivity and reduces postprandial blood glucose when taken with meals, especially in people with insulin resistance or metabolic syndrome; the effect is modest but can be combined with other dietary interventions and does not generate relevant drug interactions.
The doses studied range from 3 to 15 grams daily depending on indication: 3 g before bedtime for sleep (the most common form), 5-10 g/day divided into two servings for collagen support or metabolic health; it is sold as a powder (it has a slightly sweet, pleasant taste and dissolves easily in water) or in capsules, although given the effective doses the powder is much more practical and economical.
Glycine has an exceptionally good safety profile: practically no adverse effects at the doses studied (some people report mild nausea at very high doses or when taken on an empty stomach), with no relevant specific contraindications; theoretical caution is advisable in people taking clozapine (an atypical antipsychotic with described drug interactions) and it is advisable to consult first in people with advanced kidney disease because of the protein load involved in metabolizing it.
Information, not medical advice. Scientific evidence reflects the quality of the studies.