Evidence Comparison
Melatonin vs Glycine
For sleep — which one has better evidence?
🏆 Winner for sleep
Melatonin
Scores 62% vs 58% in evidence strength
Head-to-Head Comparison
0.5-3mg per night
3-5g before bed
30-60 minutes before desired sleep time. For jet lag: take at destination bedtime starting 1-2 days before travel.
30-60 minutes before sleep for sleep benefits
Immediate-release for sleep onset; extended-release for sleep maintenance. Sublingual for faster onset.
Free-form glycine powder
$5-15/mo
$8-15/mo
3 studies
3 studies
Evidence for sleep
Melatonin
62%Reduces sleep onset latency by 7-12 minutes on average. More of a timing signal than a sedative. Benefits are modest for general insomnia.
Glycine
58%Multiple controlled trials show glycine at 3g before bed improves subjective sleep quality, reduces sleep latency, and decreases next-day fatigue without sedation.
Mechanism of Action
Melatonin
Melatonin binds to MT1 and MT2 receptors in the suprachiasmatic nucleus (SCN) of the hypothalamus, the brain's master circadian clock. MT1 receptor activation promotes sleepiness by inhibiting wake-promoting signals from the SCN. MT2 receptor activation shifts circadian phase timing, which is why me...
Read full review →Glycine
Glycine promotes sleep through multiple mechanisms. Primarily, it acts on NMDA receptors in the suprachiasmatic nucleus, triggering peripheral vasodilation that lowers core body temperature — a key physiological signal for sleep onset. This thermoregulatory effect mimics the natural drop in body tem...
Read full review →⏱️ Time to Effect
Melatonin
Onset of drowsiness signal. Easier to fall asleep.
Sleep onset improves by 7-12 minutes on average.
Circadian rhythm shifts if timing is consistent. Jet lag resolves.
No tolerance develops. Same dose remains effective indefinitely.
Glycine
Core body temperature begins to drop (0.1-0.2°C). Relaxation onset.
Improved sleep onset. Works acutely — no loading period required.
Consistent sleep quality improvement. Next-day alertness may improve.
No tolerance develops. Safe for long-term nightly use at 3g.
🤝 Can You Take Both?
✅ These can generally be taken together safely. Many people stack both for complementary effects.
However, always start one at a time so you can identify which is responsible for any effects you notice.
📋 The Bottom Line
Choose Melatonin if:
- ✓ frequent travelers crossing time zones
- ✓ shift workers
- ✓ those with delayed sleep phase (night owls)
Choose Glycine if:
- ✓ individuals with poor sleep quality
- ✓ those seeking non-sedating sleep support
- ✓ people wanting collagen support