The supplement industry has discovered sleep. Walk into any pharmacy or scroll through almost any wellness account and you will encounter magnesium glycinate, melatonin gummies, ashwagandha capsules, tart cherry concentrate, and a dozen other products all promising deeper, faster, and more restorative sleep. Sales of sleep supplements in the UK have grown considerably over the past few years, and the interest is not unreasonable: poor sleep is genuinely common, prescription sleeping tablets carry real risks with long-term use, and the instinct to try something natural first is, broadly speaking, sensible.
What I want to do here is give you an honest picture of what the research actually shows for each of these supplements. I should say at the outset that I am not going to dismiss them. Some of them have genuine evidence behind them, for particular people in particular circumstances. The problem is the gap between how they are marketed and what the science actually demonstrates, and I think understanding that gap will either help you use them more effectively or, in some cases, redirect you towards what is actually causing your sleep problem.
A few things worth understanding before we start. Most of the trials in this area are small, short in duration, and focused on specific populations, most commonly older adults, people with formally diagnosed insomnia, or people with particular medical conditions such as diabetes or polycystic ovary syndrome. The evidence base for a generally healthy person in their thirties or forties who sleeps poorly and feels fatigued is considerably thinner than the online discourse would suggest. I will flag this as we go, because it matters enormously when you are deciding whether something is likely to help you.
Magnesium: Glycinate, Bisglycinate, and L-Threonate
If there is one supplement that has come to dominate the sleepmaxxing conversation in the past couple of years, it is magnesium, and specifically the forms marketed as most bioavailable: magnesium glycinate, magnesium bisglycinate, and magnesium L-threonate. The claims are consistent: faster sleep onset, deeper sleep, fewer night awakenings.
The most honest summary of the magnesium evidence is this: it probably helps some people fall asleep a little faster, mostly older adults with deficient intake, and the effect is real but modest. In younger, well-nourished sleepers, the evidence is very thin indeed.
The mechanism proposed is biologically plausible, which is part of why this has gained traction. Magnesium is involved in regulating GABA receptors, the brain's primary calming neurotransmitter system, and may play a role in reducing cortisol levels. People who are genuinely deficient in magnesium might sleep more poorly, and supplementation could help correct that. The question is whether most of the people buying magnesium supplements are actually deficient, and whether supplementing above what food provides produces a measurable improvement.
The most rigorous summary of the clinical evidence comes from a 2021 systematic review and meta-analysis published in BMC Complementary Medicine and Therapies [1]. The researchers identified three randomised controlled trials comparing oral magnesium against placebo for insomnia. The total sample was 151 people, all of them older adults, from three countries. The pooled finding was that magnesium reduced the time it took to fall asleep by an average of 17.36 minutes compared to placebo. In concrete terms, if someone was taking an average of 45 minutes to fall asleep, magnesium might reduce that to around 28 minutes. That is a meaningful improvement if falling asleep is your particular problem. The confidence interval for this finding ranged from about 7 minutes to 27 minutes, meaning the benefit could be anywhere in that range. Total sleep time improved by about 16 minutes on magnesium compared to placebo, but this did not reach statistical significance. All three trials were rated at moderate to high risk of bias, and the overall quality of evidence was graded as low to very low.
The 2025 magnesium bisglycinate trial, the largest placebo-controlled trial of its kind to date, enrolled 155 adults aged 18 to 65 years with self-reported poor sleep quality and randomised them to 250mg of elemental magnesium daily for four weeks [2]. The magnesium group showed a significantly greater reduction in insomnia severity scores compared to the placebo group. The effect size, however, was small (Cohen's d of 0.2, for those familiar with statistics). Importantly, when researchers looked at objective sleep data from wrist-worn Oura Ring recordings, there were no significant differences between the groups. People reported feeling better, but the tracker did not confirm it in objective measurements. The researchers themselves suggested that those with lower baseline dietary magnesium intake showed the most benefit, which fits the idea that supplementation helps most when there is a genuine deficit to correct.
Magnesium L-threonate, which has attracted considerable attention because of its proposed ability to cross the blood-brain barrier more effectively, was examined in an 80-person randomised trial of adults aged 35 to 55 [3]. Participants took 1g of magnesium L-threonate or placebo daily for 21 days. The magnesium group maintained better sleep scores over the intervention period, with some improvements in deep sleep and REM scores from Oura Ring data. However, the trial was short, the sample was self-selected for people reporting sleep problems, and the effect sizes were modest. A separate 2026 trial of 100 adults aged 18 to 45 found improvements in cognitive performance but no significant group differences in objective sleep measures from Oura Ring data, though subjective sleep-related impairment did improve in participants with more severe baseline problems [4].
The 2022 systematic review by Arab and colleagues, which pooled 7,582 subjects from nine studies including both observational and interventional research, found that while observational data consistently linked higher dietary magnesium intake with better sleep quality, the randomised controlled trials produced contradictory findings [5]. Some showed improvements in sleep efficiency, time, and latency; others showed no significant effects.
If you regularly sleep poorly, feel wired despite being tired, and your diet is not particularly rich in magnesium-containing foods such as nuts, seeds, leafy greens, and dark chocolate, magnesium supplementation is a reasonable thing to try. If your sleep problem feels more structural — waking unrefreshed despite apparently adequate hours — the mechanism does not fit and the supplement is unlikely to address what is actually happening.
My reading of this evidence is as follows. Magnesium supplementation is inexpensive, generally well tolerated, and may produce a modest reduction in time to fall asleep, particularly in older adults or people with dietary deficiency. The evidence for its effects in healthy younger adults with good dietary intake is essentially absent, because those trials have not been done at scale with sufficient quality. The proposed mechanism (GABA support and cortisol reduction) makes most sense for sleep difficulty driven by anxiety or stress. It makes essentially no sense for sleep difficulty driven by structural upper airway problems, which is often what is actually going on in people who have tried everything and still wake exhausted.
Melatonin
Melatonin is perhaps the most discussed sleep supplement in the world, and it occupies an interesting regulatory position in the UK, where low-dose melatonin is available over the counter while higher doses remain prescription-only. The hormone is produced naturally by the pineal gland in response to darkness, rising in the evening to signal to the brain that it is time to sleep. Taking it exogenously is, in principle, supplementing your natural signalling system.
The evidence for melatonin is better than for most supplements, but it is also more specific to particular populations and particular types of sleep problem than the marketing acknowledges.
Melatonin works best for people whose body clock is shifted late, not for people who simply have poor quality sleep. The distinction matters enormously, because treating the wrong problem with the right drug still fails.
The most cited meta-analysis, published in PLOS ONE in 2013, analysed 19 randomised controlled trials involving 1,683 subjects [6]. Melatonin reduced the time to fall asleep by an average of 7.06 minutes compared to placebo (confidence interval 4.4 to 9.8 minutes). It increased total sleep time by an average of 8.25 minutes (confidence interval 1.7 to 14.8 minutes). Overall sleep quality improved by a small but statistically significant amount. These effects are real. They are also modest in absolute terms. Falling asleep 7 minutes faster and sleeping 8 minutes longer is a meaningful finding at the population level, but it is worth being realistic about what that means for an individual night.
More recent and more granular analyses suggest the picture is considerably more specific. A 2022 systematic review and meta-analysis by Choi and colleagues, which looked specifically at chronic insomnia, found that melatonin was not significantly effective for sleep onset latency, total sleep time, or sleep efficiency in adults with non-comorbid insomnia [7]. The American Academy of Sleep Medicine does not recommend melatonin as a treatment for primary insomnia in adults. The European sleep medicine guidelines, published in 2017, similarly rate the evidence for melatonin in insomnia treatment as low to very low.
Where melatonin does have genuinely strong evidence is in circadian rhythm conditions, most notably delayed sleep phase disorder (sometimes called delayed sleep phase syndrome), where the body clock is shifted significantly later than social norms require [8]. A meta-analysis looking specifically at this condition found that melatonin reduced sleep onset latency by 23.27 minutes (confidence interval 4.8 to 41.7 minutes) and advanced the internal circadian clock by over an hour. This is a large and clinically meaningful effect. For someone who genuinely cannot fall asleep until 2am or 3am, and who wakes in the afternoon feeling fine but cannot function at 7am, melatonin at the right dose and time is genuinely useful. The same analysis found that wake-up time and total sleep time did not change significantly, which reinforces that the primary effect is on circadian phase rather than on general sleep architecture.
The dosing question is one that most online guidance gets badly wrong. A 2024 systematic review and dose-response meta-analysis by Cruz-Sanabria and colleagues, covering 26 randomised trials published between 1987 and 2020, found that melatonin's effects on sleep onset latency and total sleep time peaked at around 4mg per day [9]. Most people who buy melatonin over the counter take 5mg, 10mg, or even higher doses, which the evidence suggests provides no additional benefit over lower doses and may suppress endogenous melatonin production with continued use. The same analysis found that timing matters considerably: taking melatonin approximately three hours before desired bedtime produced better results than the common practice of taking it thirty minutes before bed. This is because melatonin works by shifting the circadian clock rather than by sedating you directly, and that process takes time.
Most people take far too much melatonin at the wrong time. The evidence suggests 0.5mg to 2mg, taken two to three hours before your target bedtime, is likely more effective than a 10mg gummy taken immediately before lights out.
If you are buying melatonin in the UK and wondering whether it is right for you, the honest answer is that it is most likely to help if you consistently struggle to fall asleep at a socially normal time and tend to wake later than you need to. If your problem is waking repeatedly through the night, waking unrefreshed despite adequate hours, or persistent daytime fatigue, the evidence does not support melatonin as a solution. Those patterns warrant proper investigation rather than a supplement.
Ashwagandha
Ashwagandha (Withania somnifera) is an adaptogenic herb from Ayurvedic medicine that has been studied for stress, anxiety, and sleep over the past decade. The proposed mechanism is primarily through the hypothalamic-pituitary-adrenal axis: ashwagandha appears to reduce cortisol levels and modulate the stress response, which may secondarily improve sleep.
A 2021 systematic review and meta-analysis by Cheah and colleagues pooled data from five randomised controlled trials encompassing 400 participants [10]. Ashwagandha showed a small but statistically significant effect on overall sleep, with a standardised mean difference of minus 0.59, which is roughly equivalent to a moderate improvement in sleep quality scores. The effects were more pronounced in people with a diagnosed insomnia disorder, with treatment doses of at least 600mg per day, and with treatment duration of at least eight weeks.
Several individual trials are worth noting. Langade and colleagues randomised 60 patients (29 in the treatment group, 19 in the placebo group after dropouts) to 300mg of ashwagandha root extract twice daily for ten weeks [11]. Sleep onset latency was significantly shorter after ashwagandha compared to placebo, with sleep efficiency scores also improving. Deshpande and colleagues studied 150 healthy subjects with non-restorative sleep over six weeks, giving 120mg of a standardised ashwagandha extract or placebo once daily [12]. They reported a 72 per cent improvement in self-reported sleep quality in the treatment group compared to 29 per cent in the placebo group, with objective actigraphy data also showing improvements in sleep efficiency and onset. These are encouraging results. They are also in relatively small, short trials, with considerable placebo effects evident in control groups.
The most important caveat with ashwagandha is that a significant proportion of the trials have been funded by manufacturers of ashwagandha products, and several are conducted by the same research group in India. This does not invalidate the findings, but it is a reason for appropriate caution about the magnitude of the effects reported. A meta-analysis of ashwagandha for anxiety by Akhgarjand and colleagues, covering twelve trials with over a thousand participants, found significant reductions in anxiety and perceived stress, but rated the overall certainty of evidence as low [13].
My sense of ashwagandha is that it is probably genuinely useful for people whose sleep difficulties are primarily driven by stress and anxiety, and whose cortisol regulation is genuinely dysregulated. For people in high-pressure work environments who find it difficult to switch off in the evenings, there is at least a plausible biological rationale and some supporting evidence. For people whose sleep problem is structural (such as airway problems causing repeated arousals), it addresses a different mechanism entirely and is unlikely to produce meaningful benefit. It is also worth noting that there are no long-term safety data for ashwagandha, and some reports of liver injury with high doses, which means it warrants more caution than magnesium, which has a much more established safety profile.
The Sleepy Girl Mocktail: Tart Cherry Juice
The sleepy girl mocktail, a blend of tart cherry concentrate, magnesium powder, and sparkling water, became one of the more viral sleep trends of 2023 and 2024. The theoretical basis is that tart cherries contain small amounts of naturally occurring melatonin and other phytochemicals that might support sleep. It is not an unreasonable idea. The question is whether the amount of melatonin in tart cherry juice is clinically significant.
Tart cherry juice contains real melatonin. Whether there is enough of it in a typical serving to make a meaningful difference to your sleep is a more contested question than the viral posts suggest.
The foundational human trial was published in the European Journal of Nutrition in 2012 by Howatson and colleagues [14]. Twenty healthy adults consumed either tart cherry juice concentrate or a placebo for seven days in a randomised, double-blind, crossover design. Urinary melatonin levels were significantly elevated in the cherry juice group, and there were significant increases in time in bed, total sleep time, and sleep efficiency. The effect on total sleep time was modest but measurable. This is a well-designed small trial and it showed something real, even if the sample size limits how much we can extrapolate from it.
A pilot study by Pigeon and colleagues tested tart cherry juice in 15 older adults with chronic insomnia over two weeks [15]. Compared to a placebo drink, tart cherry juice was associated with significant reductions in wake time after sleep onset (in other words, less time lying awake through the night), though differences in sleep latency, total sleep time, and sleep efficiency did not reach statistical significance against placebo. Effect sizes were described as moderate and comparable to valerian and some melatonin studies.
A 2025 systematic review by Barforoush and colleagues, which searched databases through January 2025 and identified seven relevant interventional studies, found that three reported significant improvements in sleep indicators such as duration, efficiency, or onset time, and three reported increases in melatonin levels after tart cherry consumption [16]. The reviewers noted substantial differences in dose, duration, and participant characteristics between studies, and concluded that while tart cherry consumption may improve sleep quality, the available evidence remains limited and heterogeneous. A separate 2022 trial in 44 adults found no significant effects of Montmorency tart cherry supplementation on any sleep measures compared to placebo [17].
My reading of this is that tart cherry juice probably does have a small, genuine biological effect on melatonin levels and may modestly improve some sleep parameters, particularly in older adults or people with mild insomnia. It is unlikely to produce dramatic improvements. It is also a pleasant thing to drink in the evening, involves no significant safety concerns for most people, and if it becomes part of a wind-down routine (see the sleep hygiene article), that ritual element itself has independent value.
Kiwi Fruit Before Bed
The kiwi fruit claim, that eating two kiwis an hour before bed improves sleep, circulates widely online and is invariably cited with reference to a single study published in 2011 in the Asia Pacific Journal of Clinical Nutrition by Lin and colleagues [18]. I want to be clear about the scale of this evidence base before we discuss what the study found.
The trial enrolled 24 participants, two male and 22 female, aged 20 to 55, in a free-living self-controlled design (which means there was no separate control group and participants served as their own comparison before and after). They ate two kiwi fruits one hour before bedtime every night for four weeks. The Pittsburgh Sleep Quality Index score improved significantly. Sleep onset latency reduced by 35.4 per cent. Total sleep time increased by 13.4 per cent and sleep efficiency improved by 5.41 per cent. In concrete terms, if someone was taking 30 minutes to fall asleep, a 35.4 per cent reduction would mean falling asleep about 10 minutes faster. That is not trivial.
The proposed mechanism is the serotonin content of kiwi fruit, alongside antioxidants and folate. Serotonin is a precursor to melatonin, which makes the mechanism at least biologically plausible. However, one trial of 24 people with no separate control group, conducted over four weeks, is insufficient to recommend kiwi fruit as a clinical intervention. What we can say is that it is an interesting observation that warrants proper investigation, and that eating two pieces of fruit before bed carries no meaningful risks for most people. I am also directed to an excellent blog post on this topic by Dr Hugh Selsick, a colleague whose thinking on sleep I greatly respect, at hughselsick.com, which gives a sensible perspective on where this sits in the broader landscape of sleep research.
A Final Word on Supplements Generally
Before we move on, I want to make a point that applies to all of these supplements and is particularly relevant to anyone who has tried several of them without sustained benefit. The single most important question when a supplement fails to improve your sleep is not which supplement to try next. It is whether your sleep problem has a different cause entirely, one that no supplement can address.
Obstructive sleep apnoea, a condition in which the upper airway partially or completely collapses during sleep, causes fragmented, unrestorative sleep that is completely indistinguishable from other causes of poor sleep at the subjective level. No supplement addresses an obstructed airway. If you feel persistently unrefreshed on waking, snore, wake with a dry mouth or headache, or have been told you appear to stop breathing during sleep, the answer is not another supplement. It is a conversation with a doctor about whether a sleep study is warranted.
References
[1] Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a Systematic Review and Meta-Analysis. BMC Complementary Medicine and Therapies. 2021;21(1):125. Three RCTs in 151 older adults; 17.36 minutes' reduction in sleep onset latency versus placebo; total sleep time improvement of 16 minutes did not reach statistical significance; all trials at moderate-to-high risk of bias with low to very low quality evidence.
[2] Schuster J, et al. Magnesium Bisglycinate Supplementation in Healthy Adults Reporting Poor Sleep: A Randomized, Placebo-Controlled Trial. Nature and Science of Sleep. 2025. 155 adults aged 18–65; 250mg elemental magnesium daily for 4 weeks; significant reduction in Insomnia Severity Index scores (Cohen's d=0.2); no significant differences in objective Oura Ring sleep metrics.
[3] Hausenblas HA, et al. Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: a randomized controlled trial. Sleep Medicine: X. 2024. 80 adults aged 35–55; 1g/day MgT or placebo for 21 days; significant improvements in subjective sleep measures; Oura Ring data showed improvements in some parameters.
[4] Lopresti A, et al. The effects of magnesium L-threonate (Magtein) on cognitive performance and sleep quality in adults: a randomised, double-blind, placebo-controlled trial. Frontiers in Nutrition. 2026. 100 adults aged 18–45; 2g daily Magtein or placebo for 6 weeks; cognitive improvements and subjective sleep-related impairment reduction but no significant group differences in objective sleep outcomes.
[5] Arab A, et al. The Role of Magnesium in Sleep Health: a Systematic Review of Available Literature. Biological Trace Element Research. 2022;201(1):121–128. 7,582 subjects across 9 studies; observational studies consistently showed association between magnesium and sleep quality; RCTs showed contradictory findings.
[6] Ferracioli-Oda E, et al. Meta-Analysis: Melatonin for the Treatment of Primary Sleep Disorders. PLOS ONE. 2013;8(5):e63773. 19 RCTs, 1,683 subjects; melatonin reduced sleep onset latency by 7.06 minutes (95% CI 4.37–9.75); increased total sleep time by 8.25 minutes (95% CI 1.74–14.75); small but significant improvement in sleep quality.
[7] Choi K, et al. Efficacy of melatonin for chronic insomnia: Systematic reviews and meta-analyses. Sleep Medicine Reviews. 2022;61:101576. 24 RCTs of chronic insomnia; melatonin not significantly effective for sleep onset latency, total sleep time, or sleep efficiency in adult non-comorbid insomnia; more effective in children and adolescents.
[8] van Geijlswijk IM, et al. The use of exogenous melatonin in delayed sleep phase disorder: a meta-analysis. Sleep. 2010;33(12):1605–1614. 5 trials in 91 adults and 4 trials in 226 children with delayed sleep phase disorder; melatonin advanced melatonin onset by 1.18 hours and sleep onset by 0.67 hours; reduced sleep onset latency by 23.27 minutes.
[9] Cruz-Sanabria F, et al. Optimizing the Time and Dose of Melatonin as a Sleep-Promoting Drug: A Systematic Review and Dose-Response Meta-Analysis. Journal of Pineal Research. 2024;76:e12985. 26 RCTs, 1,689 observations; effects peaked at 4mg/day; administration 3 hours before bedtime more effective than 30 minutes before; insomnia status and timing significant predictors of efficacy.
[10] Cheah KL, et al. Effect of Ashwagandha (Withania somnifera) extract on sleep: A systematic review and meta-analysis. PLOS ONE. 2021;16(9):e0257843. 5 RCTs, 400 participants; standardised mean difference −0.59 overall; stronger effects in insomnia subgroup, at doses ≥600mg/day, and duration ≥8 weeks.
[11] Langade D, et al. Efficacy and Safety of Ashwagandha Root Extract in Insomnia and Anxiety: A Double-blind, Randomized, Placebo-controlled Study. Cureus. 2019;11(9):e5797. 60 patients (40 treatment, 20 placebo); 300mg extract twice daily for 10 weeks; significant improvements in sleep onset latency, sleep efficiency, and anxiety scores.
[12] Deshpande A, et al. A randomized, double blind, placebo controlled study to evaluate the effects of ashwagandha (Withania somnifera) extract on sleep quality in healthy adults. Sleep Medicine. 2020;72:28–36. 150 healthy subjects; 120mg Shoden daily for 6 weeks; 72% vs 29% self-reported improvement; significant improvements in objective actigraphy-derived sleep efficiency, onset, and wake after sleep onset.
[13] Akhgarjand C, et al. Does Ashwagandha supplementation have a beneficial effect on the management of anxiety and stress? A systematic review and meta-analysis. Phytotherapy Research. 2022;36(11):4115–4124. 12 trials, 1,002 participants; significant reductions in anxiety and stress; overall evidence certainty rated as low.
[14] Howatson G, et al. Effect of tart cherry juice (Prunus cerasus) on melatonin levels and enhanced sleep quality. European Journal of Nutrition. 2012;51(8):909–916. 20 healthy volunteers; randomised double-blind crossover; 7 days of cherry juice concentrate; significant increases in urinary melatonin, time in bed, total sleep time, and sleep efficiency.
[15] Pigeon WR, et al. Effects of a Tart Cherry Juice Beverage on the Sleep of Older Adults with Insomnia: A Pilot Study. Journal of Medicinal Food. 2010;13(3):579–583. 15 older adults with chronic insomnia; randomised double-blind crossover; 2-week intervention; significant reductions in wake after sleep onset; moderate effect sizes.
[16] Barforoush F, et al. The Effect of Tart Cherry on Sleep Quality and Sleep Disorders: A Systematic Review. Food Science and Nutrition. 2025. 7 interventional studies reviewed; 3 showed significant sleep improvements; 3 showed increased melatonin levels; substantial heterogeneity in dose, duration and populations.
[17] Hillman AR, et al. Montmorency tart cherry supplementation does not impact sleep, body composition, cellular health, or blood pressure in healthy adults. Nutrition and Health. 2022. 44 participants; juice or capsule versus placebo for 30 days; no significant differences in any sleep measure.
[18] Lin HH, et al. Effect of kiwifruit consumption on sleep quality in adults with sleep problems. Asia Pacific Journal of Clinical Nutrition. 2011;20(2):169–174. 24 participants (2 male, 22 female); ages 20–55; self-controlled design; 4 weeks of 2 kiwifruit 1 hour before bedtime; 35.4% reduction in sleep onset latency; 13.4% increase in total sleep time.
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