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VITAMINS & SUPPLEMENTS · GUIDE

Sleep Supplements Compared: Melatonin, Magnesium, Glycine and L-Theanine

Melatonin, magnesium, glycine and L-theanine side by side for sleep: what trials and reviews found, how strong each body of evidence is, safety points, and what is missing.

Content last updated . This page has not been medically reviewed.

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Quick answer
Melatonin has the most research. A 2013 meta-analysis of 19 trials found it shortened the time to fall asleep by about 7 minutes, a small effect. [2] Magnesium, glycine and L-theanine have fewer and smaller trials, and their results are mixed or based mostly on self-rated sleep. [3][6][8] We found no trial that compares these four directly, so this page cannot say which is better. None is proven to treat insomnia. Lasting sleep trouble needs a clinician. [1][11]

Side by side

MelatoninMagnesiumGlycineL-theanine
What it isA hormone the body makes that is linked to the sleep-wake cycle; sold as a supplement. [1]An essential mineral. [10]An amino acid. [5]An amino acid found mainly in tea. [8]
Forms and where it comes fromPills, gummies and liquids; label accuracy varies widely. [1]Several salts (citrate, oxide, glycinate and others); see the forms page. [3][10]Powder or capsules; also a large part of collagen. [7]Capsules and tablets; also tea and matcha. [8][9]
What it has been studied forJet lag, delayed sleep-wake phase disorder, anxiety before surgery, and insomnia. [1][2]Sleep and insomnia in adults, including older adults. [3][4]Sleep quality, and tiredness after short sleep. [5][6][7]Self-rated sleep, stress and anxiety. [8][9]
Evidence labelPromising but limited (specific uses); insufficient evidence as a routine insomnia aid. [1][2]Mixed. [3]Promising but limited; few trials. [6][7]Promising but limited. [8]
Amounts used in studies (information only)Not pooled here. A meta-analysis found longer trials and higher amounts had larger effects on sleep latency. [2]Trials in older adults used under 1 g of magnesium compounds up to three times a day, per the review's conclusion. [4]3 g of glycine before bed for three nights in sleep-restricted adults. [5]400 mg a day of one branded L-theanine for 28 days (30 adults). [9]
Absorption or bioavailability evidenceProper evidence not found in the sources we read.Differs by form; see the forms page. [3]A 2026 review found glycine-containing supplements generally raised blood glycine, with some dose dependence. [7]Proper evidence not found in the sources we read.
Safety and cautionsSee the safety points above. Older adults may have daytime drowsiness; guidelines advise against use in dementia. [1]Diarrhea at higher amounts. [10] Ask first with kidney problems or regular medicines.Long-term safety not established in the sources we read. [6]Few problems reported in small, short trials. [9]
Who it may suit (and who should ask first)Studied in jet lag and delayed sleep timing. Ask first: children, pregnancy, epilepsy, blood thinners, older adults. [1]Studied in adults with poor sleep. Ask first: kidney problems, regular medicines. [3][10]Studied in healthy adults with short sleep. Ask first: pregnancy, children, medicines. [5][6]Studied in healthy and stressed adults. Ask first: pregnancy, children, medicines. [8][9]
Direct comparison trialsNone found in what we read.None found in what we read.None found in what we read.None found in what we read.

How to read the differences

The four are different kinds of things: a hormone, a mineral and two amino acids. A result for one does not carry over to another, or to a different form, amount or group of people. Melatonin's effect is small, about 7 minutes faster to fall asleep and about 8 minutes more sleep in one pooled analysis. [2] Magnesium and L-theanine reviews rely on self-rated sleep, and the magnesium trials were rated low to very low certainty. [3][4][8] The glycine sleep trials are few and small, and the longer studies in healthy people had a high risk of bias. [6][7] The L-theanine review noted a lack of studies of "pure" L-theanine. [8] In the 28-day L-theanine trial, the placebo group improved nearly as much as the treated group on perceived stress. [9] Better sleep on a self-rated scale is not the same as treating insomnia.

What to check on a label

  • The exact form: for example which magnesium salt, and whether it states elemental magnesium.
  • The amount per serving, and whether the product is a blend that hides individual amounts.
  • Whether other sleep ingredients are added, which can double up with melatonin or other products you take.
  • Whether the product is a gummy or flavored, and keep it away from children. [1]
  • Independent testing, since melatonin labels often did not match contents. [1]

Related pages

This page is information only, not medical advice. Ask a clinician or pharmacist about insomnia and about your medicines.

Frequently asked questions

Which is best for sleep: melatonin, magnesium, glycine or L-theanine?

We found no trial comparing them. Melatonin has the most research, with a small effect on falling asleep. [2]

Does melatonin treat insomnia?

Two guidelines found too little evidence to recommend it for chronic insomnia, and NCCIH notes cognitive behavioral therapy is the first-line choice. [1]

Are melatonin gummies accurate?

Not always. In one 2023 study, 22 of 25 gummies were inaccurately labeled. [1]

Does magnesium help with sleep?

Results are inconsistent and the certainty is low to very low. [3]

When should I see a clinician about sleep?

The NHS advises seeing a GP if changing habits has not helped, if trouble has lasted months, or if it affects daily life. [11]

More details: evidence, limits and cautions

The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.

Quick safety points
  • Melatonin and children: a CDC report cited by NCCIH estimated 11,000 emergency visits from 2019 to 2022 for children aged 5 and under who swallowed melatonin without supervision. Store all sleep products out of reach. [1]
  • Melatonin labels: a 2023 study found 22 of 25 melatonin gummies mislabeled, with 74 to 347 percent of the labeled amount. [1]
  • Melatonin and medicines or conditions: people with epilepsy or on blood thinners need medical supervision. Research in pregnancy and breastfeeding is lacking. [1]
  • Magnesium: more than 400 mg for a short time can cause diarrhea, and the NHS says 400 mg or less a day from supplements is unlikely to cause harm. [10]
  • Glycine and L-theanine: the trials are small and short, so long-term safety is not established. In one 28-day trial of L-theanine, adverse events resolved by the end of the study. [9]
  • Pharmacy sleep aids are not meant for long use, and the NHS advises checking with a doctor before taking anything for sleep problems. [11]
References
  1. NCCIH, Melatonin: What You Need To Know. Read 2026-10-24.
  2. Ferracioli-Oda E et al., Meta-analysis: melatonin for the treatment of primary sleep disorders. PLoS One 2013. Read 2026-10-24 (abstract via Europe PMC).
  3. Lopresti AL et al., Magnesium supplementation for sleep in adults: a systematic review of randomized controlled trials. J Diet Suppl 2026. Read 2026-10-24 (abstract).
  4. Mah J, Pitre T, Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complement Med Ther 2021. Read 2026-10-24 (abstract).
  5. Bannai M et al., The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol 2012. Read 2026-10-24 (abstract).
  6. Soh J et al., The effect of glycine administration on the characteristics of physiological systems in human adults: a systematic review. GeroScience 2024. Read 2026-10-24 (abstract).
  7. Fan Z et al., Glycine bioavailability and sleep-related outcomes following oral glycine and collagen supplementation: a scoping review. J Diet Suppl 2026. Read 2026-10-24 (abstract).
  8. Bulman A et al., The effects of L-theanine consumption on sleep outcomes: a systematic review and meta-analysis. Sleep Med Rev 2025. Read 2026-10-24 (abstract).
  9. Moulin M et al., Safety and efficacy of L-theanine supplementation for 28 days in healthy adults with moderate stress. Neurol Ther 2024. Read 2026-10-24 (abstract).
  10. NHS (UK), Other vitamins and minerals. Read 2026-10-24.
  11. NHS (UK), Insomnia. Read 2026-10-24.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.