Glycine is the simplest amino acid in the body and the most underrated. Most people take 1-3g before bed, where it gently improves sleep quality without sedation. The other reason to consider it is glutathione, your body's main antioxidant, which is rate-limited by glycine availability and tends to drop with age, chronic stress, and metabolic dysfunction.

The practical use case is two-fold. As a sleep aid before bed helps you fall asleep faster, sleep more deeply, and wake up less foggy, useful especially when stress, travel, or short sleep windows are the issue. As a foundational amino acid for older adults or anyone with metabolic issues, 5-7g per day (often paired with N-acetylcysteine) supports glutathione synthesis, mitochondrial function, and insulin sensitivity. It's one of the cheapest, safest supplements you can take.

Glycine is also the most abundant amino acid in collagen, so it has a theoretical role in supporting skin and connective tissue. In practice, if connective tissue is the goal, collagen peptides plus vitamin C is the better-evidenced protocol because it delivers proline and hydroxyproline alongside glycine. More on that in the deep-dive.

Deep-dive

Dosage:

• For sleep: 3g is the dose that's been studied. Some people report effects at 500mg-1,500mg. 30-60 min before bed.
• For glutathione/antioxidant support (older adults, chronic stress, metabolic dysfunction): 50-100 mg/kg/day (3.5-7g for a 70kg adult), often combined with NAC (the "GlyNAC" protocol). This is the chronic, daily, foundational dose used in the Baylor aging trials.
• Upper end: Doses up to 60-90g/day have been used in clinical trials (schizophrenia) without serious adverse events, but you don't need anywhere near this. Most practical use sits between 3g (sleep only) and 7g (sleep + glutathione).
• Timing: Glycine is rapidly absorbed (plasma rises within 10 min, peaks around 30-60 min). Sleep dose: take 30-60 min before bed. Glutathione protocol: split AM and PM, doesn't matter much when. No need to cycle.
• Form: Plain glycine powder is by far the cheapest. Sweet-tasting (the name comes from the Greek for "sweet"), dissolves easily in water or tea. Capsules are convenient but expensive at chronic doses. Magnesium glycinate provides ~14% glycine by weight.
• Stacks: Pairs well with magnesium glycinate or magnesium threonate plus L-theanine for sleep. Pairs with NAC for the glutathione protocol. If connective tissue support is the goal, collagen peptides + vitamin C is the better-evidenced choice, with or without extra free glycine on top.

Here's what you can expect:

For sleep, you should notice falling asleep slightly faster (5-15 min reduction in sleep onset is typical), sleeping more deeply, and waking up feeling more rested rather than groggy within the first few nights. The effect is subtle, not knockout-style. If you're expecting heavy sedation you'll be disappointed. If you're expecting to feel more recovered the next morning, that's the realistic target.

For glutathione, metabolic health, and antioxidant capacity, there's no subjective signal at all. You take it (with NAC) because the mechanistic case is reasonable in older or metabolically struggling populations, not because you'll feel different. If you're under 40, lean, eating adequate protein, and metabolically healthy, this use case is largely theoretical for you, and NAC alone may give you most of the benefit anyway.

No tolerance, no withdrawal. You can stop and restart at any time. You can also forget a dose with no real consequence.

Side effects & risks:

• GI upset is the main side effect, usually only above 5-10g taken at once. Mild nausea, loose stools, or stomach discomfort. Splitting the dose across the day fixes it.