Glycine is a cheap, well-tolerated amino acid. Its most reliable use is a gentle bedtime aid that may modestly improve sleep quality and next-day alertness. Supporting the body's main antioxidant looks promising in older adults. Blood-sugar and lifespan claims stay unproven in people. Mild stomach upset and drowsiness are the main concerns. (Full Review)

Protocol

Sleep Dose

3 g before bed

Powder dissolved in water, 30–60 min before bed; some use 1–2 g

Glutathione Support

Pair with N-acetylcysteine

GlyNAC approach for older adults; gram-level doses of each, split through the day

Titration

Start 1 g, build to 3 g

Increase over several days only if needed; split higher daily intakes to improve tolerance

Time to effect

Sleep

First night

Taken acutely before bed

Glutathione

Weeks

Develops over weeks of consistent use

Metabolic

Weeks

Where present, develops over weeks of consistent use

Benefits

Medium: Improved subjective sleep quality; support for glutathione production in older adults

Low: Improved markers of glucose metabolism; reduced formation of advanced glycation end products; connective tissue and collagen support

Speculative: Lifespan extension; anti-inflammatory and cardioprotective effects

Contraindications

Severe kidney or liver impairment

Inborn errors of glycine metabolism

Clozapine use

Pregnancy and breastfeeding

Key Interactions

Sedatives and sleep medications (benzodiazepines such as diazepam, "Z-drugs" such as zolpidem, sedating antihistamines)

Other sedating supplements (magnesium, GABA, valerian, L-theanine)

Antispasticity agents and muscle relaxants

Risk & Side Effects

Medium: Mild gastrointestinal upset

Low: Daytime drowsiness or sedation; interaction risk in specific clinical contexts

Speculative: Theoretical concern with severe kidney or liver impairment

Monitoring

Marker	Target	Why
Fasting glucose	75–90 mg/dL	Tracks any metabolic benefit
Fasting insulin	2–5 µIU/mL	Gauges insulin sensitivity
HbA1c	< 5.4%	Longer-term glucose control
eGFR	> 90 mL/min/1.73m²	Confirms clearance organ health before higher doses
Glutathione (or oxidized-to-reduced ratio)	Higher reduced fraction preferred	Tracks antioxidant-support goal

Cadence: Sleep: reassess after 1–2 weeks. Metabolic or glutathione goals: recheck labs at roughly 3 months, then every 6–12 months.

Qualitative Assessment

Sleep quality and time to fall asleep
Next-day energy and daytime alertness
Subjective recovery and joint or skin comfort
General sense of calm before bed

Glycine for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment