Melatonin vs Glycine: what to choose and for whom

Choosing between melatonin and glycine makes sense only when it is clear which particular sleep problem is bothering you. Falling asleep at three in the morning because of a shifted schedule and waking up tired after eight hours in bed are different situations, and the remedies for them are different. The editorial team offers a practical map of choice taking into account studies and clinical guidelines.

First — determine the type of problem

Sleep problems are conventionally divided into several groups. The first is disturbances of sleep timing: a person may sleep well but «not at the right time», as with jet lag, shift work or the habit of going to bed very late. The second is difficulty falling asleep or frequent awakenings with a normal schedule.

The third group is sleep that seems sufficient in duration but does not bring a feeling of rest. The fourth is disturbances caused by external or medical factors: snoring with apnea, restless legs syndrome, pain, anxiety, caffeine or alcohol in the evening.

Melatonin and glycine work at different points on this map. Melatonin is strongest precisely where the biological clock is shifted. Glycine was studied mainly as a means of improving the subjective quality of sleep in people who complain of inadequate rest.

For the fourth group no supplement is a solution: snoring with breathing pauses, severe daytime drowsiness or insomnia lasting more than three months require medical examination.

When melatonin is more logical

Flights across several time zones are a classic indication. The Cochrane review concluded that melatonin, taken at bedtime by the local time of the arrival point, reduces the manifestations of jet lag, especially on eastward flights.

Delayed sleep phase, when a person regularly cannot fall asleep until late at night but sleeps well if allowed to sleep in until midday. The clinical guidelines of the American Academy of Sleep Medicine on circadian disorders support properly timed melatonin intake for such patients.

Older people with insomnia: in the EU a prescription prolonged-release melatonin 2 mg is registered for patients aged 55 and over. This is associated with the age-related decline in the body's own secretion of the hormone.

Athletes who often travel to competitions or are forced to train and perform late in the evening can also consider melatonin for adjusting their schedule — preferably together with a sports physician.

When glycine may suit

Glycine is of interest to people who fall asleep without particular problems but wake up unrested. It is precisely in this group that Japanese researchers recorded an improvement in the subjective assessment of sleep and morning well-being after 3 g of glycine before bed.

For those who want to avoid a hormonal effect on the circadian system or for whom melatonin causes a morning «heaviness», glycine may be a gentler alternative for a short trial.

For people during periods of partial sleep deprivation: in the study by Bannai et al. (2012) glycine reduced daytime fatigue and improved some performance indicators when sleep duration was limited.

It is worth remembering the dose: the effects concern 3 g, that is, powder or large-dose capsules, not 100 mg sublingual tablets. Glycine in powder has a sweetish taste and dissolves easily in water.

Comparative map of choice

We have summarized typical situations in a table. It shows not a «winner» but the appropriateness of each remedy depending on the context.

As can be seen from the scheme, the areas of application almost do not overlap. Therefore the question «which is stronger» is less useful than the question «which particular problem am I solving».

Who needs caution

Melatonin is not recommended without a doctor for pregnant and breastfeeding women, children and adolescents, people with autoimmune diseases, epilepsy, as well as those taking anticoagulants, immunosuppressants or fluvoxamine.

It is also important that the clinical guideline of the American Academy of Sleep Medicine on chronic insomnia does not recommend melatonin as a means of treating insomnia with sleep onset and maintenance in adults — because of the weakness of the evidence.

• Do not get behind the wheel if you feel drowsy after taking melatonin.
• Do not combine sleep aids with alcohol.
• Choose products from proven manufacturers: the melatonin content in supplements can differ significantly from what is stated.
• People taking antipsychotics, in particular clozapine, should discuss glycine with a doctor.

Glycine is well tolerated, but this does not mean it can be taken for months without assessing the effect. If sleep has not improved in 2–3 weeks, there is no sense in continuing — it is better to look for the cause together with a specialist.

Editorial conclusions

Melatonin is the choice for those whose problem is in sleep timing: jet lag, shift work, delayed sleep phase. Glycine is an option for a short trial for those who sleep enough but wake up unrested.

For chronic insomnia the first line remains cognitive behavioral therapy, not supplements, and signs of apnea or other disorders require examination.

Regardless of the choice, sleep hygiene — a regular schedule, darkness, limiting caffeine and screens in the evening — provides the foundation without which no supplement works fully.

The editorial team also recommends our materials on melatonin and magnesium, 5-HTP and melatonin and on sleep recovery after intense training.

References

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