Sleep supplements are one of the fastest-growing categories in the industry, driven by widespread sleep issues and a population increasingly reluctant to use prescription medications. Some of these supplements have genuine evidence. Others are riding the wellness wave. Here is our evidence ranking.
Tier 1: Meaningful evidence
Magnesium (glycinate or threonate forms)
Magnesium is the sleep supplement with the broadest evidence base and most plausible mechanism. Roughly 50% of adults in developed countries do not meet the recommended dietary intake for magnesium, making this one of the few supplements addressing a genuine widespread deficiency.
Magnesium glycinate and magnesium threonate are the preferred forms for sleep. Glycinate binds magnesium to glycine (itself a sleep-supportive amino acid) and has good bioavailability with minimal GI side effects. Threonate (Magtein) has specific evidence for crossing the blood-brain barrier. A 2012 RCT found that magnesium supplementation significantly improved sleep quality scores, sleep time, and melatonin levels in elderly adults with insomnia.
The critical distinction is form. Magnesium oxide, the cheapest and most common form, has roughly 4% bioavailability and primarily acts as a laxative. If your magnesium supplement is giving you loose stools but not improving your sleep, you are probably taking the wrong form. Dose: 200-400mg elemental magnesium from glycinate or threonate, taken 30-60 minutes before bed.
Melatonin (at the right dose)
Melatonin has strong evidence, but with a massive caveat: the effective dose is 0.3-0.5mg, roughly one-tenth of what most products contain. Melatonin is a circadian signal, not a sedative. It tells your brain that it is time to sleep; it does not force sleep.
A 2013 meta-analysis in PLOS ONE pooling 19 RCTs found melatonin significantly reduced sleep onset latency (by about 7 minutes) and increased total sleep time (by about 8 minutes). These are modest but real effects when dosed appropriately. The evidence is strongest for jet lag and shift work where circadian rhythm is disrupted.
The problem is that nearly every commercial melatonin product is dramatically overdosed. At 5-10mg, you are getting 10-30 times the physiological dose, which can cause next-day grogginess, vivid nightmares, and may suppress your natural melatonin production over time. If you use melatonin, look for low-dose (0.3-0.5mg) options or cut standard tablets.
Tier 2: Promising evidence
L-Theanine (100-200mg)
L-theanine, an amino acid found in tea, promotes relaxation without sedation by increasing alpha brain wave activity. Multiple RCTs show improved subjective sleep quality and reduced anxiety at bedtime. A 2019 RCT in Nutrients found that 200mg L-theanine significantly improved sleep quality scores compared to placebo. It does not directly induce sleep but reduces the mental activation that prevents sleep onset.
L-theanine is particularly useful for people whose sleep issues stem from an overactive mind at bedtime rather than a circadian rhythm problem. The safety profile is excellent, with virtually no reported adverse effects.
Glycine (3g)
Glycine is an underappreciated sleep aid with solid mechanistic and clinical evidence. Multiple studies show that 3g of glycine taken before bed reduces core body temperature (a key sleep trigger), improves subjective sleep quality, and reduces next-day fatigue. A 2012 RCT demonstrated significant improvements in sleep quality and reduced daytime sleepiness.
The mechanism is well-understood: glycine acts on NMDA receptors in the suprachiasmatic nucleus, helping to lower core body temperature, which is a critical physiological signal for sleep initiation. It is cheap, safe, and tastes slightly sweet, making it easy to take.
What is mostly marketing
Valerian root has inconsistent evidence -- meta-analyses show conflicting results and methodological limitations across studies. 5-HTP has theoretical merit as a serotonin precursor but limited sleep-specific clinical data. CBD for sleep has almost no rigorous RCT data despite enormous marketing spend; most positive studies used doses far higher than typical consumer products.
Our recommendation
A reasonable evidence-based sleep stack looks like: magnesium glycinate (300-400mg elemental), optionally L-theanine (200mg), and glycine (3g). This combination addresses multiple sleep mechanisms without dependency risk. Add low-dose melatonin (0.3-0.5mg) only if you have circadian disruption from jet lag or shift work. And always address sleep hygiene first -- no supplement can compensate for screens at midnight, irregular schedules, and caffeine after noon.