Health Reference Library

Which supplements for sleep have evidence?

This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.

Summary

Four options carry evidence. Magnesium comes first, strongest in people who are low or older, with sleep onset roughly 17 minutes faster in the 2021 meta-analysis and better sleep quality with bisglycinate over weeks. L-theanine at 200 mg improved sleep latency and disturbance over four weeks. Ashwagandha at 600 mg a day for eight weeks or more is clearest in people with insomnia. Glycine at 3 g before bed has small trials with subjective benefit. Melatonin is prescription-only in the UK. Valerian, CBD and 5-HTP have weak or absent evidence. None beats an earlier, consistent bedtime and a dark room, and the right pick depends on why sleep is failing.

How it works

Magnesium is a cofactor in GABA signalling and in the enzymes that set the circadian clock, so people running low, which is common on a low-fibre diet or with heavy training, sleep better when it is corrected; people who are replete see less. Theanine raises alpha-wave activity and dampens the stress response, which is why it helps the racing-mind type of poor sleep. Ashwagandha lowers cortisol and acts on GABA receptors, slowly, which is why the trials run eight weeks. Glycine lowers core body temperature slightly, the same signal the body uses to start sleep. None of them sedates; they remove obstacles, which is why a wired mind responds to theanine and a depleted body to magnesium, and why the first question is which obstacle is yours.

Timing

Theanine works within the first week; magnesium over two to four weeks in people who were low; ashwagandha over eight weeks; glycine within nights. Judge any one at four weeks on mornings, not on night one.

Safety profile

Ashwagandha is avoided in pregnancy, with thyroid overactivity and with liver disease, and is reviewed with the GP on thyroid or sedative prescriptions. Magnesium above 400 mg elemental loosens bowels and is dosed with care in kidney disease. Theanine is well tolerated. Glycine is well tolerated at 3 g. Snoring with pauses, gasping or severe daytime sleepiness is sleep apnoea until shown otherwise and needs a GP, not a supplement. Nutri365 checks for interactions and contraindications before suggesting any of these.

Special populations

Over-60s and people with low dietary magnesium see the largest magnesium effect. Perimenopausal sleep disruption is often vasomotor and is addressed on the [perimenopause page](/apps/learn/perimenopause-symptoms-and-what-actually-helps) before any supplement. Shift workers and new parents have a schedule problem that no supplement solves. Pregnancy excludes ashwagandha.

Guideline positions

Mah and Pitre 2021, systematic review and meta-analysis of magnesium for insomnia in older adults: sleep onset about 17 minutes faster, low-quality evidence. Abbasi 2012, randomised trial of 500 mg magnesium in older adults with insomnia: improved sleep efficiency, time, and onset latency. Schuster 2025, magnesium bisglycinate in healthy adults: improved sleep quality over the trial period. Hidese 2019, 200 mg L-theanine for four weeks in 30 healthy adults, crossover: Pittsburgh Sleep Quality Index improved, with sleep latency, sleep disturbance and sleep-aid-use subscales reduced against placebo. Cheah 2021, meta-analysis of five ashwagandha trials: small but significant sleep improvement, larger with insomnia, 600 mg a day and eight weeks or more. Lopresti 2019, ashwagandha 240 mg for 60 days: lower stress scores and morning cortisol. NHS sleep guidance puts routine, light and caffeine first.

Practical framework

The supplement is matched to the reason. Where falling asleep takes ages and the mind will not stop, theanine runs at 200 mg an hour before bed for four weeks, with the timeline on the [theanine page](/apps/learn/does-theanine-help-with-stress-and-sleep-what-dose-did-the-trials-use). Where waking is unrefreshed, with cramps, a low-fibre diet, heavy training, or age over 60, magnesium bisglycinate runs at 200 to 400 mg elemental in the evening, with the week-by-week expectation on [magnesium for sleep](/apps/learn/magnesium-for-sleep-expected-timeline-week-by-week). Where the picture is stressed, wired and tired for months, ashwagandha runs at 600 mg a day for eight weeks, read on the [ashwagandha page](/apps/learn/does-ashwagandha-work-for-stress-and-sleep-what-dose). Where sleep is light and broken rather than slow to start, glycine runs at 3 g before bed, per the [glycine page](/apps/learn/does-glycine-help-sleep-and-what-dose-did-the-research-use). Whichever applies, one runs at a time for four weeks, judged on how mornings feel rather than on a sleep score, against a set wake time, morning light and caffeine stopped by early afternoon, all on [how to fall asleep faster](/apps/learn/how-to-fall-asleep-faster-what-the-evidence-supports). Nutri365 reads which obstacle applies, and whether the chosen option is moving anything over those four weeks, checks for interactions and contraindications, and refers questions outside scope to a health specialist.

Common misconceptions

Melatonin is not available over the counter in the UK and the gummies sold online are unregulated. Magnesium oxide is poorly absorbed and is the wrong form for sleep. Taking all four at once tells you nothing about which one helped. And a sleep score improving while mornings feel the same is not success.

Sources

  1. Mah J, Pitre T 2021. Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complementary Medicine and Therapies. PMID: 33865376
  2. Abbasi B, Kimiagar M, Sadeghniiat K, Shirazi MM, Hedayati M, Rashidkhani B 2012. The effect of magnesium supplementation on primary insomnia in elderly: a double-blind placebo-controlled clinical trial. Journal of Research in Medical Sciences. PMID: 23853635
  3. Schuster J, Cycelskij I, Lopresti A, Hahn A 2025. Magnesium Bisglycinate Supplementation in Healthy Adults: sleep quality. Nature and Science of Sleep. PMID: 40918053
  4. Hidese S, Ogawa S, Ota M, Ishida I, Yasukawa Z, Ozeki M, Kunugi H 2019. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients. PMID: 31623400
  5. Cheah KL, Norhayati MN, Husniati Yaacob L, Abdul Rahman R 2021. Effect of Ashwagandha (Withania somnifera) extract on sleep: A systematic review and meta-analysis. PLoS One. PMID: 34559859
  6. Lopresti AL, Smith SJ, Malvi H, Kodgule R 2019. An investigation into the stress-relieving and pharmacological actions of an ashwagandha extract. Medicine (Baltimore). PMID: 31517876

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