Melatonin for Sleep: What the Research Actually Says

What Melatonin Actually Does

Melatonin is a hormone produced by your pineal gland in response to darkness. Its job is not to knock you out. It's to signal to your body that night is coming. Think of melatonin as your circadian system's announcement of dusk, not as a sedative. This distinction matters because it explains why melatonin works for some problems and why it fails for others.

Your body naturally produces melatonin in a carefully timed rhythm. Levels are suppressed during daylight (especially blue light exposure), begin rising in the afternoon as dusk approaches, peak around 2–4 AM, and drop again toward morning. This rhythm is controlled by your suprachiasmatic nucleus (SCN), your brain's master clock, which receives light input via specialized retinal cells called intrinsically photosensitive retinal ganglion cells.

DLMO: The Marker That Matters

Sleep researchers use Dim Light Melatonin Onset (DLMO) to measure when your circadian system thinks night has begun. DLMO is the time your melatonin level reaches 2–3 pg/mL in dim light conditions (less than 50 lux). It's the most reliable marker of your circadian phase, more precise than wake time or bed time.

For most people, DLMO occurs roughly 1.5–3 hours before habitual sleep time. If your DLMO is at 9 PM but you're trying to sleep at 10 PM, your circadian system is already in "night" mode—melatonin supplementation at this point may do little. If your DLMO is at 11 PM and you need to sleep at 10 PM, your circadian system isn't ready, and melatonin supplementation earlier in the evening might help shift your DLMO earlier. This is why timing melatonin correctly matters so much more than the dose.

The Dose Question: 0.5mg vs 5mg vs More

One of the biggest misunderstandings about melatonin is the dose. Most over-the-counter melatonin supplements contain 3–10 mg per tablet. Studies suggest this is 5–10 times higher than necessary. Your body naturally produces only 0.2–0.3 mg of melatonin per night.

Research by sleep chronobiologist Michael Thorpy and others found that 0.5 mg taken at the right time shifts circadian phase more effectively than 5 mg at the wrong time. A meta-analysis in Sleep Medicine Reviews concluded that doses above 1–2 mg provide no additional benefit for healthy adults and may increase side effects like grogginess or dependency. For circadian phase shifting, efficacy plateaus at around 0.5–1 mg. For sleep onset, slightly higher doses (1–3 mg) may help some people feel drowsy, but this is separate from the circadian timing benefit.

The Phase Response Curve: Timing Is Everything

The Phase Response Curve (PRC) to melatonin shows exactly how the timing of melatonin doses shifts your circadian clock. This is where melatonin's power lies. Taking melatonin in the evening (after DLMO but before your usual bedtime) has minimal effect on phase. Taking melatonin in the afternoon (4–9 hours before your natural DLMO) can shift your circadian phase earlier by 30–120 minutes, depending on dose and individual sensitivity.

Conversely, taking melatonin in the early morning (after normal sleep offset but before your body's natural dawn) can delay your circadian phase—useful for people with early wake times. This is why melatonin works so well for jet lag: when you arrive in a new time zone, taking melatonin at the right local time can reset your circadian clock to match the new environment within a few days, far faster than light exposure alone.

When Melatonin Helps—And When It Doesn't

Melatonin is evidence-based for circadian phase problems: jet lag (especially eastbound travel), shift work adjustment, and Delayed Sleep Phase Syndrome. A Cochrane systematic review found strong evidence that melatonin speeds adaptation to jet lag by 1–2 days.

However, melatonin shows minimal benefit for simple insomnia—waking up in the middle of the night, difficulty staying asleep, or low sleep quality in people with normal circadian timing. If your DLMO is properly timed but you struggle with sleep maintenance, melatonin is unlikely to help. In these cases, cognitive behavioral therapy for insomnia, sleep restriction, or other behavioral interventions have stronger evidence.

Melatonin also has limited evidence for Seasonal Affective Disorder and is not a substitute for light therapy. For most healthy adults with no circadian disorder, high-dose melatonin at bedtime may feel mildly sedating (which can help sleep onset), but it's not correcting an underlying biological problem—it's just a mild sedative effect, which fades with repeated use.