Melatonin is the most widely sold sleep supplement in the United States, yet it is almost universally misunderstood. Most people take it as a sleep drug — something that makes them drowsy when taken at bedtime. This is not what melatonin does, why it was prescribed, or what the research supports. Understanding melatonin's actual role clarifies when it helps, when it doesn't, and why the dose most Americans take is probably 5–20 times higher than optimal.
What Melatonin Actually Is
Melatonin is a hormone produced by the pineal gland — a small structure deep in the brain — in response to darkness. It is a circadian timing signal, not a sedative. Its primary function is to signal to the body that it is night — triggering the downstream biological events associated with nighttime: slight core temperature reduction, metabolic slowdown, and the preparation for sleep. It does not directly cause sleep or produce drowsiness in the way a benzodiazepine or antihistamine does.
In humans, melatonin secretion begins approximately 2–3 hours before habitual sleep onset, peaks in the middle of the night, and declines in the second half of the night. It is suppressed almost entirely by bright light — particularly short-wavelength (blue) light. This is why light exposure in the evening delays melatonin onset and shifts the circadian clock later.
How Melatonin Supplementation Works
Supplemental melatonin works by acting as an exogenous timing signal — it tells the brain "it is now night at this moment." If taken at the right time relative to the circadian clock, it can shift the timing of sleep onset. This is why melatonin is effective for:
- Jet lag: Taking melatonin at the local destination bedtime helps the brain recalibrate to the new time zone. It is one of the most evidence-supported uses — reducing jet lag severity by approximately 50% in multiple Cochrane-reviewed trials.
- Shift work: Melatonin taken before daytime sleep shifts the circadian clock, improving sleep quality during unusual hours.
- Delayed sleep-wake phase disorder (DSWPD): Taking low-dose melatonin 5–6 hours before natural sleep onset advances the circadian clock, making earlier sleep onset possible over several weeks.
- Children with autism spectrum disorder or ADHD: These populations frequently have delayed melatonin onset and respond well to low-dose melatonin supplementation.
When Melatonin Doesn't Work
For the most common reason adults take melatonin — difficulty falling or staying asleep due to stress, anxiety, hyperarousal insomnia — melatonin is not the appropriate tool. The American Academy of Sleep Medicine does not recommend melatonin for chronic insomnia disorder, noting insufficient evidence for clinically meaningful benefit.
Insomnia driven by anxiety, hyperarousal, or poor sleep habits is not a melatonin deficiency problem. Melatonin cannot override an activated nervous system any more than wearing pyjamas can make someone calm. The appropriate treatment for insomnia is CBT-I — see our guide on insomnia causes and remedies and our free Insomnia Relief Plan tool.
The Dose Problem: Why 5–10mg Is Almost Always Too Much
This is one of the most important melatonin facts most people don't know. The physiological concentrations of melatonin in the blood during natural melatonin secretion are in the picogram per millilitre range — roughly equivalent to a dose of 0.1–0.3mg of supplemental melatonin. The smallest widely available US supplement dose is 1mg; 5mg and 10mg products are extremely common.
Research by MIT's Wurtman Lab found that 0.3mg of melatonin is as effective for advancing the circadian clock as higher doses — and produces blood levels in the physiological range. Doses above 1mg flood melatonin receptors, produce supraphysiological levels, and may actually cause next-morning grogginess rather than improving nighttime sleep quality. Long-term high-dose supplementation may downregulate the body's own melatonin production, although the evidence on this is still developing.
The practical recommendation: Start with 0.5mg of immediate-release melatonin, taken 1–2 hours before intended sleep onset. If using for jet lag, take it at the local bedtime at the destination. If using for delayed sleep phase, take it 5–6 hours before natural sleep onset. There is no evidence that exceeding 1mg produces greater benefit.
Factors That Suppress Melatonin Production
- Evening light exposure: The most powerful suppressor. Even ordinary room lighting (200 lux) suppresses melatonin production significantly; smartphone and tablet screens (blue-enriched light) at normal brightness cause a 90-minute delay in melatonin onset.
- Age: Melatonin secretion amplitude decreases significantly with age — older adults produce much less melatonin than younger people. This partially explains why older adults have earlier and lighter sleep patterns.
- Beta-blockers: These common blood pressure medications suppress melatonin production and are an under-recognised cause of insomnia in older adults.
- Non-steroidal anti-inflammatory drugs (NSAIDs): High-dose or regular NSAID use mildly suppresses melatonin.
For more on the supplements market and what the evidence actually supports for sleep, see our article on melatonin safety and overdose risk. For practical sleep improvement beyond supplements, use our free Sleep Score tool.
Health disclaimer: This article is for informational purposes only. Consult your physician before starting any supplement, particularly if you take medications or have underlying health conditions.
About the author: Morgan Wells is a certified sleep analyst and wellness writer with over a decade of experience in behavioral sleep health. Learn more about Morgan.