Melatonin is one of the best-selling sleep supplements globally, yet it is widely misunderstood — taken at the wrong dose, wrong time, and for the wrong indications. The evidence for melatonin is specific: it is highly effective for certain circadian timing problems, modestly effective for jet lag, and largely ineffective as a general sleep aid for primary insomnia. Getting the indication right makes the difference between a useful tool and a placebo.
What melatonin actually is
Melatonin is not a sedative. It does not directly induce sleep the way a sleeping pill does. It is a chronobiotic hormone — a signal of biological darkness, secreted by the pineal gland in the absence of light, that communicates to the body that it is nighttime and times the circadian clock accordingly. Melatonin secretion begins 2–3 hours before habitual sleep onset (the dim-light melatonin onset, or DLMO), remains elevated throughout the night, and is suppressed by morning light. Its primary physiological role is timing — telling the clock when night begins — not inducing sleep per se. This is why melatonin works best when there is a timing problem (circadian displacement) and produces minimal benefit when sleep difficulty has other causes (anxiety, hyperarousal, sleep apnea, insomnia behavioral patterns).
Where the evidence is strong: circadian timing problems
Jet lag: melatonin taken at the destination bedtime (0.5–5mg) on the first few nights after eastward travel — the direction where circadian readjustment is hardest — consistently accelerates circadian realignment and reduces jet lag symptoms. The Cochrane review on jet lag (Herxheimer 2002, updated) found melatonin effective, rating it one of the few well-supported interventions for transmeridian travel. Delayed sleep phase syndrome (DSPS): DSPS is a circadian disorder characterized by a very late natural sleep time (2–6am) and inability to fall asleep earlier. Low-dose melatonin (0.5mg) taken 5–7 hours before desired sleep onset (typically around 9–10pm) effectively advances the clock over several weeks. This is the indication with the strongest evidence for melatonin’s circadian-shifting effect. Shift workers: melatonin taken before daytime sleep (after a night shift) improves daytime sleep duration and quality for shift workers. The effect size is moderate but consistent.
Where the evidence is weak: primary insomnia
For chronic insomnia without a circadian component — the most common form, driven by hyperarousal and perpetuating behavioral factors — melatonin produces modest effects on sleep onset latency (typically 7–12 minutes faster) and minimal effects on total sleep time or quality in meta-analyses. The 2013 Cochrane review (Buscemi et al.) concluded that melatonin was not effective for most primary sleep disorders. Several national sleep medicine guidelines recommend against melatonin as a first-line treatment for chronic insomnia, instead recommending CBT-I. The discrepancy between melatonin’s popularity and its evidence base for primary insomnia is significant — it is a common case of a supplement being used for an indication where it is not well-supported.
Dosing: less is more
The most important practical point about melatonin supplementation is that the doses sold commercially in many countries (1–10mg, sometimes 20mg) are pharmacologically much higher than what the body produces physiologically (typically 0.1–0.3mg per night peak). Research consistently shows that low doses (0.3–0.5mg) are as effective as higher doses for circadian timing effects, and higher doses are no more effective — they simply produce higher blood concentrations that may suppress the body’s endogenous melatonin production with chronic use. For jet lag and circadian shifting: 0.5mg is the evidence-supported dose, not 5–10mg. The large doses commonly sold reflect marketing and manufacturing convenience, not clinical evidence. Melatonin has an excellent short-term safety profile; long-term safety data for chronic daily use are more limited, though no major adverse effects have been demonstrated.
Conclusion: use melatonin for timing, not as a sedative
Melatonin works for what it is: a circadian timing signal. It is effective for jet lag (take at destination bedtime, starting the night of arrival), for advancing the clock in delayed sleep phase (low dose, 5–7 hours before desired sleep onset), and for improving daytime sleep in shift workers. It is a poor choice for primary insomnia driven by anxiety, hyperarousal, or poor sleep habits — CBT-I addresses those causes far more effectively.
If you use melatonin: take 0.5mg (not 5–10mg), at the appropriate time relative to your desired sleep window, and ensure the room is dark after taking it — exogenous melatonin combined with continued bright light exposure is largely self-defeating.
