Ranked honestly: melatonin is a circadian timing signal — strong for jet lag and shifted clocks, worth ~7 minutes of faster onset in ordinary insomnia. Magnesium shows small benefits mainly in older adults and the deficient. Valerian's meta-analyses land on inconsistent, mild effects; L-theanine relaxes measurably but has thin insomnia data; glycine has two small trials; chamomile and lavender are pleasant with small files; CBD's insomnia evidence remains poor. Antihistamine "PM" products build tolerance within days and carry anticholinergic costs. None treats insomnia's conditioning or apnea's airway — CBT-I outperforms the entire aisle with effects that last after stopping.
The scorecard
The sleep aisle is the supplement industry's second-largest, aimed at a symptom with high placebo response and two root causes — conditioning and airways — that no capsule addresses. Against placebo-controlled trials:
| Ingredient | Verdict | What trials show |
|---|---|---|
| Melatonin | Moderate for timing uses; limited for insomnia | Jet lag and clock-shifting: genuinely supported. Ordinary insomnia: ~7 min faster onset. Dose 0.5–3 mg; US label accuracy is its own hazard. |
| Magnesium | Limited | Small onset/efficiency gains in older and deficient sleepers (FAQ); thin in the young and replete. |
| Valerian | Mixed | Dozens of trials, inconsistent methods and extracts; meta-analyses find subjective improvement without objective change; occasional morning grogginess. |
| L-theanine | Limited | Reliable calm-without-sedation markers; sleep-outcome trials small (some pediatric ADHD data); 200 mg is the studied evening dose. |
| Glycine | Limited | Two small Japanese trials (3 g pre-bed): better subjective quality and next-day alertness; awaiting replication for a decade. |
| Ashwagandha | Limited | Modest sleep gains, clearest in insomnia-with-stress at 600 mg — the stress page's evidence wearing pajamas. |
| Chamomile, lavender (oral/aroma) | Insufficient | Small pleasant files; tea's ritual may be its active ingredient. |
| CBD / cannabis | Insufficient→cautionary | FAQ verdict: thin trials, tolerance and rebound, unregulated products. |
| Antihistamine "PM" aids | Works briefly, costs after | Days-scale tolerance, architecture costs, anticholinergic load — the aisle's worst habit. |
| Tart cherry, kiwi, GABA, 5-HTP | Insufficient | Pilot-scale curiosities; 5-HTP adds serotonergic-interaction risk. |
| Multi-ingredient "sleep blends" | Insufficient | Sub-dose rows above plus melatonin at random milligrams; untested as sold. |
What the shelf structurally can't do
Chronic insomnia runs on conditioning — a bed trained into a wakefulness cue — and CBT-I beats medications in trials precisely because it retrains that machinery, with response rates near 70–80% and durability nothing swallowed can match. And a large slice of "bad sleep" is apnea — an airway problem for which every sedating agent on the table is somewhere between useless and counterproductive (muscle relaxation worsens collapse). The aisle's honest ceiling is the margins: timing nudges, relaxation assists, deficiency corrections — worth their modest prices only after the two root causes have been addressed or excluded, an order of operations the FAQ's final answer turns into a protocol.
The honest playbook
- Schedule and light first — fixed wake time, morning outdoors, evening dim: the free circadian therapy melatonin imitates.
- CBT-I for any 3-month insomnia — clinician, group or validated app; the treatment guidelines put first and shelves never mention.
- Screen the apnea signature — snoring, pauses, unrefreshing sleep, morning headaches → home test, not chamomile.
- Experiment singly and score honestly (FAQ 4's sequence) — 2–4 weeks, diary-judged, losers dropped.
- Retire the PM pills gently and the nightcap honestly (alcohol fragments the back half of every night it starts).
Sleep formulas we review are graded against this scorecard in the supplement research section.
Frequently asked questions
Does magnesium deserve its TikTok reputation for sleep?
Partially. Trials cluster in older adults with poor sleep — small improvements in onset and efficiency at 250–500 mg — and in the magnesium-deficient, where correction plausibly helps everything magnesium touches. In younger replete adults the direct evidence is thin, and "magnesium glycinate transformed my sleep" testimonials ride the same fluctuation-and-expectation physics as every aisle on this site. Cheap, safe at sensible doses (loose stools cap it; kidney disease needs advice), reasonable to trial for a month — with honest scoring.
Why are antihistamine PM pills a bad habit if they clearly knock me out?
Because the knockout fades and the costs don't: tolerance to diphenhydramine's sedation develops within days, sleep architecture is degraded (less deep sleep for more unconsciousness), next-day grogginess lingers, and the anticholinergic load — dry mouth, constipation, urinary retention — associates with cognitive risk in older adults on the memory page's warning list. They're engineered for occasional use and marketed into nightly habits.
What about CBD or cannabis for sleep?
The controlled evidence is thinner than the market: CBD trials for insomnia are small, mixed and often confounded by anxiety effects; THC shortens onset but suppresses REM, tolerates quickly, and rebounds badly on stopping — heavy users' insomnia on quitting is a withdrawal signature. Add unregulated product variability and drug interactions (CBD inhibits liver enzymes), and it's a research area wearing a retail costume.
Is there any stack that makes sense for a stressed poor sleeper?
The defensible sequence isn't a stack: fix the schedule and light first, run CBT-I (apps count), screen for apnea if the signature fits — then, if experimenting, one agent at a time for 2–4 weeks with a sleep diary: melatonin 0.5–1 mg timed correctly if the clock is late, magnesium if older or plausibly deficient, ashwagandha if stress is the engine, L-theanine if a racing mind at lights-out is the specific complaint. Keep what the diary vindicates; drop the rest.
References
- NCCIH. Melatonin: What You Need To Know (2022). https://www.nccih.nih.gov/health/melatonin-what-you-need-to-know
- NHLBI. Insomnia (2022). https://www.nhlbi.nih.gov/health/insomnia
- U.S. Food and Drug Administration. Dietary Supplements (2024). https://www.fda.gov/food/dietary-supplements
This page discusses supplement ingredients or categories. It may mention a commercial product, with disclosure. It is general health information, not personal medical advice. Read our editorial policy and medical review policy.