Does glycine reset my body clock?

No. It amplifies the nightly core temperature drop that accompanies sleep onset, but it has not been shown to shift circadian phase.

Will it help jet lag?

There is no evidence for that. Timed light exposure and melatonin are the phase-shifting tools.

3 g taken 30-60 minutes before bed, which is the dose used in nearly all human studies.

Can I take it with melatonin?

They work through different routes and no interaction is described, but add one at a time so you know what is working.

No dependence or withdrawal has been described.

Outcome

Moderate Evidence

Glycine for Circadian Rhythm

Human trials show 3 g glycine before bed improves subjective sleep quality, shortens sleep onset, and reduces next-day fatigue. It works by promoting peripheral vasodilation and lowering core body temperature — a natural sleep-onset signal within circadian physiology.

Overview

Glycine taken before bed lowers core body temperature, and core temperature drop is one of the body's main circadian sleep signals. That is the whole basis for the circadian rhythm claim.

The temperature effect is well documented in small human studies, and it plausibly reinforces the evening phase of the sleep-wake cycle. Glycine is cheap, tastes mildly sweet and has an unusually clean safety record. What it is not is a circadian phase-shifting agent in the way light or melatonin are. There is no good evidence that glycine moves your body clock, helps jet lag or corrects shift-work misalignment. It supports the nightly temperature dip rather than resetting timing.

No studies are currently linked to this pairing

This page reflects established physiology and conventional dosing rather than trial data attached to this outcome in our library.

How It Works

Glycine crosses the blood-brain barrier and acts both as an inhibitory neurotransmitter at glycine receptors and as a co-agonist at the NMDA receptor glycine site. The relevant action here appears to be in the suprachiasmatic nucleus, the master circadian pacemaker.

Animal work indicates glycine acts on NMDA receptors in the suprachiasmatic nucleus to trigger peripheral vasodilation, increasing heat loss through the skin of the hands and feet and lowering core temperature. In humans, evening glycine reproduces exactly this pattern - warmer extremities, cooler core. Because the nightly fall in core temperature is a normal circadian cue that accompanies sleep onset, amplifying it may reinforce the evening arm of the rhythm. This is a supportive effect on an existing rhythm, not an input that shifts clock phase.

Dosing & Protocol

Nearly all human work has used the same simple protocol.

Context	Dose	Form	Timing
Standard studied dose	3 g	Glycine powder or capsules	30-60 minutes before bed
Lower trial dose	1-2 g	Powder	Before bed, if 3 g feels unnecessary
Higher explored range	5-10 g	Powder	Before bed; no added benefit demonstrated for temperature
Assessment window	1-2 weeks	-	Effects are same-night rather than cumulative

Timing carries the effect

Glycine's temperature drop is acute. Taken in the morning it does nothing useful for circadian purposes.

Evidence

There are currently no studies linked to this pairing in our library, so no study list is shown.

The wider literature consists of a handful of small Japanese studies, several with industry involvement, showing that 3 g of glycine before bed lowers core temperature, shortens time to sleep onset and improves next-day subjective fatigue in people with poor sleep. Animal studies provide the suprachiasmatic nucleus mechanism. What is missing is any direct circadian measurement. No study has shown glycine shifting dim-light melatonin onset, altering clock gene expression in humans, or helping jet lag or shift work. Sample sizes are small and independent replication is limited.

Temperature, not phase

Glycine has been shown to amplify the nightly temperature dip. It has not been shown to shift circadian phase.

Safety

Glycine is a non-essential amino acid present in ordinary protein foods and in the body's own collagen, and it has a very favourable tolerability profile at the doses used for sleep.

Mild and dose-related side effects

Nausea, soft stools or stomach discomfort occur mainly at larger doses. Reducing the dose or taking it with a little food usually resolves them.

Long-term safety data at supplemental doses are limited, though decades of use in clinical nutrition are reassuring. People with significant kidney or liver impairment should ask their clinician before adding amino acid supplements, and there is no adequate safety data in pregnancy at supplemental doses.

Interactions & Conflicts

Glycine has few interactions, but its NMDA activity is worth noting.

Interacts with	Severity	Mechanism	Action
Clozapine	moderate	Glycine has been reported to reduce clozapine efficacy	Avoid unless your psychiatrist approves
Sedatives and sleep medication	moderate	Additive sedation	Introduce cautiously and avoid driving until you know the effect
Advanced kidney or liver disease	moderate	Altered amino acid handling	Seek medical advice first
Alcohol	low	Alcohol independently disrupts sleep architecture	Expect the benefit to be masked

References

No studies are currently linked to this pairing, so no reference list is available. This section will populate as evidence is added to the library.

Frequently Asked Questions

Medical Disclaimer

The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.

Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.