Melatonin: morning or night?

Always before bed for sleep onset. Morning melatonin is only used clinically to phase-delay a circadian rhythm (advanced sleep phase disorder, jet lag travelling westbound). For jet lag travelling eastbound, take 0.5 mg at local bedtime for 3 to 5 nights after arrival. For shift workers transitioning to night shifts, take 0.5 to 3 mg at the new bedtime. For people with delayed sleep phase disorder (chronic late-bedtime pattern), take 0.5 mg 5 to 6 hours before current sleep onset, then gradually advance the dose earlier as the rhythm shifts. Never take melatonin to extend sleep duration in the middle of the night, that produces grogginess without the timing benefit.

Melatonin is not a sedative, it is a circadian timing signal. The pineal gland releases it in response to darkness, levels rise roughly 2 hours before sleep onset (dim light melatonin onset, DLMO), and the entire endogenous nightly amount is only about 0.3 mg. Supplemental melatonin works by shifting the timing of this signal forward (when taken in the evening) or backward (when taken in the morning, used to treat delayed sleep phase). The 5 mg and 10 mg doses sold in most US stores deliver 10 to 30 times the physiological amount and cause plasma melatonin to spike well above normal night-time levels, which is why higher doses cause grogginess without improving sleep onset. Low doses (0.3 to 1 mg) taken 30 to 60 minutes before target bedtime, with dim lighting and no screens after the dose, produce the cleanest sleep-onset shift with the fewest side effects.

The windows above are anchored to a conventional day, not to clock time. If you work nights or wake at midday, shift the whole pattern rather than the individual dose: treat your own waking hour as "morning" and your own wind-down hour as "night". For Melatonin the thing that matters is the relationship to your sleep and to your meals, not the number on the clock. Shift workers rotating between days and nights get the most consistent results by anchoring the dose to a fixed event, the first meal of a shift, rather than to a fixed time.

Take it later the same day if there is still a sensible slot left, with water at any point. If the day is gone, skip it and resume tomorrow. Do not double the next dose to compensate: for anything stored in the body a single miss is inconsequential, and for anything cleared quickly a double dose gives no benefit while raising the chance of side effects. Adherence over weeks matters far more than any single perfectly timed dose, which is why the best window for Melatonin is usually the one you will actually keep.

• 30–60 min before bed

  0.5–1mg sublingual or capsule in dim lighting

• When should I take melatonin for jet lag?+

  For eastbound travel, take 0.5 mg at local bedtime for 3 to 5 nights after arrival. For westbound travel, take 0.5 mg in the early evening starting 2 to 3 days before departure to phase-delay your rhythm. Pair with bright light exposure in the morning at the destination for the fastest adjustment.
• Is melatonin safe to use every night?+

  Short-term nightly use (up to a few months) appears safe in healthy adults at low doses. Long-term nightly use is less studied. For chronic insomnia, CBT-I and addressing root causes outperform melatonin and avoid any dependence concern. Use melatonin for circadian disruption (jet lag, shift work, delayed sleep phase), not as a default nightly sleep aid.
• Does it matter if I take Melatonin at a different time each day?+

  Some variation is fine. A fixed slot is recommended mainly because it is the easiest way to not forget, and because it keeps levels of quickly cleared compounds steadier. Drifting an hour or two either side of your usual time changes very little. Drifting between morning and bedtime is worth avoiding, especially if Melatonin affects your sleep or energy.
• Can I take Melatonin twice a day instead?+

  Splitting a dose is often better tolerated and, for compounds the body clears quickly, keeps blood levels steadier than one large dose. Do not increase the total by splitting it: divide the daily amount you were already taking. Check the label, some products are formulated as a single daily dose and should not be split.

• Ferracioli-Oda E, et al. PLoS ONE. 2013