The Quick Answer
Most supplement studies measure how rested people feel, not deep sleep itself, and those are separate questions. Sleep-lab studies of deep sleep are few and small: valerian and glycine shortened the time to reach deep sleep, GABA did not raise deep-sleep time, and two magnesium L-threonate trials disagree on wearable deep-sleep scores. No supplement had consistent evidence of raising deep sleep in the studies we found.
In this article
If you are searching for a deep sleep supplement, you are probably hoping to wake up feeling truly rested, and that is a reasonable thing to want. It helps to know what the research can and cannot say. Many studies measured how quickly people fall asleep or how they feel in the morning. Far fewer measured deep sleep itself, and their results are mixed.
Key takeaways
- Deep sleep is a stage. Feeling rested is a feeling. Most supplement studies measure the feeling, not the stage.
- Sleep-lab studies of deep sleep are few and small. Valerian shortened the time to reach deep sleep in 16 adults. GABA and glycine studies did not show more deep sleep.
- Wearable results for magnesium L-threonate disagree. One trial found a higher deep sleep score, and a larger one found no group differences.
- Wearables estimate deep sleep. In one study, a smart ring labeled 35% of lab-scored deep sleep as light sleep.
- No supplement had consistent evidence of raising deep sleep in the studies we found.
What is deep sleep?
Deep sleep is the stage called NREM stage 3, or slow-wave sleep. Sleep scientists describe it as the stage with the most slow, high-voltage brain waves, which gives an idea of how deep or intense sleep is. A sleep lab measures it with brain-wave recordings called polysomnography. Wearables estimate it. Our companion articles cover how much deep sleep adults get and what helps.
Feeling rested is not the same as more deep sleep
Many supplement studies ask people how they slept. A 2025 trial of magnesium bisglycinate, for example, found a modest improvement on the Insomnia Severity Index after four weeks, with a small effect size. Questionnaires like this can capture how rested someone feels, but they do not show which sleep stages changed. That is why feeling more rested and having more deep sleep are two separate questions.
What sleep-lab and wearable studies found
| Ingredient | Study | How deep sleep was measured | What it found |
|---|---|---|---|
| Valerian | Donath 2000: 600 mg extract for 14 days in 16 adults with insomnia | Sleep lab | Time to reach slow-wave sleep was shorter than with placebo (13.5 vs. 21.3 minutes). Other sleep-stage changes happened with placebo too. |
| Glycine | Yamadera 2007: 3 g before bed in adults with unsatisfactory sleep | Sleep lab | Shorter time to slow-wave sleep, with no change in sleep architecture. |
| GABA | Yamatsu 2016, in a systematic review of small studies: 100 mg for one week | Sleep EEG | Faster to fall asleep and more total non-REM time. No significant change in deep-sleep time or latency. |
| Melatonin | Several trials of 1 to 5 mg, summarized in a 2026 trial | Sleep lab | Some found changes in sleep time and stage 2, and others found no change in sleep stages. The 2026 trial did not report deep sleep separately. |
| Magnesium L-threonate | Hausenblas 2024: 1 g a day for 21 days in 80 adults | Oura ring | Higher deep sleep score than placebo. |
| Magnesium L-threonate | 2025 trial in Frontiers in Nutrition: 2 g a day for 6 weeks in 100 adults | Oura ring | No group differences in sleep outcomes. Heart rate was lower and heart rate variability was higher. |
Full citations for each study are in the references below.
Two points stand out. First, several ingredients shortened the time to reach deep sleep, which is different from increasing how much deep sleep a person gets. Second, the studies were small and mostly short, and the two magnesium L-threonate trials disagree.
Among herbs, valerian is the one with a sleep-lab study of deep sleep, and it was small. For chamomile, passionflower, hops and lemon balm, we did not find deep-sleep results. Our herbs article covers what those studies did measure.
How reliable are wearables for deep sleep?
Some of the studies above used a wearable. Wearables are good at telling sleep from wake, but stages are harder. In a 2024 study of 35 adults, one ring's deep sleep totals matched the sleep lab on average, while two other devices underestimated deep sleep by 15 and 43 minutes. In a larger study of 96 adults, the same ring labeled 35% of lab-scored deep sleep as light sleep.
Good to know
Not feeling rested despite enough hours in bed has many possible causes, and a healthcare provider can help sort them out, including whether a sleep study would be useful. Supplements carry their own considerations too. Melatonin's most common effect is daytime drowsiness, and Mayo Clinic suggests waiting about five hours after a dose before driving or using machinery. If you are pregnant, nursing, take prescription medicines or have a health condition, it is a good idea to check with your healthcare provider first.
If you are hoping for more restful nights
If you are hoping for more restful nights, it may help to decide what you want to measure. How rested you feel each morning is one useful answer. A wearable's deep sleep number is another, with the limits above. Habits such as a steady schedule are the other half of the picture, and our habits article covers them.
About Sleep Harmony
One formula, amounts you can compare
Sleep Harmony combines melatonin, calming herbs and three probiotics in one formula. Each 2-capsule serving lists 11 ingredients, including 5 mg melatonin, 100 mg valerian extract and 100 mg GABA. The studies above used 600 mg of valerian extract and 100 mg of GABA. We have not studied Sleep Harmony's effect on deep sleep, and we do not claim it increases deep sleep. The finished formula has not been clinically tested.
See the Sleep Harmony product page →The short version
Studies of supplements have shown that some ingredients shorten the time to reach deep sleep, and one wearable trial found a higher deep sleep score. We did not find a supplement with consistent evidence that it raises the amount of deep sleep. Feeling more rested is a real and separate goal, and it is the one most studies measured.
Frequently asked questions
Do deep sleep supplements work?
The studies we found do not show that any supplement consistently raises deep sleep. Some ingredients shortened the time to reach deep sleep, and one wearable trial found a higher deep sleep score, while another found no group differences. Feeling more rested is a separate question that more studies measured.
Which supplements have been studied for deep sleep?
Valerian, glycine, GABA, melatonin and magnesium L-threonate have all had studies that looked at sleep stages. Most were small. Valerian and glycine shortened the time to reach slow-wave sleep, and GABA did not change deep-sleep time in the studies reviewed.
Are there herbs for deep sleep?
Valerian is the herb with a sleep-lab study of deep sleep. It shortened the time to reach slow-wave sleep in 16 adults. For chamomile, passionflower, hops and lemon balm, we did not find deep-sleep results, though some were studied for other sleep measures.
Can a supplement increase deep sleep on my tracker?
It is possible, but the evidence is mixed. One trial found a higher deep sleep score with magnesium L-threonate, and a larger one found no group differences. Wearables also estimate deep sleep with some error, so a small change may be within the device's margin.
What are deep sleep pills?
The term is used for products marketed for sleep, most of which are dietary supplements. NIH notes that supplements do not need FDA approval before they are sold. It helps to look for a study that measured deep sleep, not only how people felt.
Does Sleep Harmony increase deep sleep?
We have not studied that, and we do not claim it does. Sleep Harmony combines melatonin, calming herbs and three probiotics in one formula. The finished formula has not been clinically tested, so we cannot say how the ingredients work together.
References
- Zisapel N. New perspectives on the role of melatonin in human sleep, circadian rhythms and their regulation. Br J Pharmacol. 2018;175(16):3190–3199. PMC6057895. Link
- Donath F, Quispe S, Diefenbach K, Maurer A, Fietze I, Roots I. Critical evaluation of the effect of valerian extract on sleep structure and sleep quality. Pharmacopsychiatry. 2000;33(2):47–53. PMID 10761819; DOI 10.1055/s-2000-7972. Link
- NIH Office of Dietary Supplements. Valerian: health professional fact sheet. (Donath study dose.) Link
- Hepsomali P, Groeger JA, Nishihira J, Scholey A. Effects of oral gamma-aminobutyric acid (GABA) administration on stress and sleep in humans: a systematic review. Front Neurosci. 2020;14:923. DOI 10.3389/fnins.2020.00923. Link
- Yamadera W, Inagawa K, Chiba S, Bannai M, Takahashi M, Nakayama K. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms. 2007;5:126–131. DOI 10.1111/j.1479-8425.2007.00262.x. Link
- Hausenblas HA, Lynch T, Hooper S, Shrestha A, Rosendale D, Gu J. Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: a randomized controlled trial. Sleep Med X. 2024;8:100121. (A corrigendum was published in Sleep Med X. 2025;9:100141.) PMID 39252819; DOI 10.1016/j.sleepx.2024.100121. Link
- The effects of magnesium L-threonate (Magtein) on cognitive performance and sleep quality in adults: a randomised, double-blind, placebo-controlled trial. Front Nutr. 2025. DOI 10.3389/fnut.2025.1729164. Link
- Thanawala S, Shah R, Lopes A, Kulkarni M, Jain B, Andhalkar N. Efficacy and safety of sustained-release melatonin capsules (2 mg) in healthy adults with poor sleep quality: a randomized, double-blind, placebo-controlled trial. Clocks Sleep. 2026;8(2):31. (Funded by the product's maker.) DOI 10.3390/clockssleep8020031. Link
- Schuster J, Cycelskij I, Lopresti A, Hahn A. Magnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomized, placebo-controlled trial. Nat Sci Sleep. 2025;17:2027–2040. PMID 40918053; DOI 10.2147/NSS.S524348. Link
- Accuracy of three commercial wearable devices for sleep tracking in healthy adults. Sensors. 2024;24(20):6532. Link
- Svensson T, Madhawa K, Nt H, et al. Validity and reliability of the Oura Ring Generation 3 (Gen3) with Oura sleep staging algorithm 2.0 (OSSA 2.0) when compared to multi-night ambulatory polysomnography: a validation study of 96 participants and 421,045 epochs. Sleep Med. 2024;115:251–263. Link
- NIH Office of Dietary Supplements. Dietary supplements: what you need to know (consumer). Link
- Mayo Clinic Staff. Melatonin side effects: What are the risks? Mayo Clinic. Link
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