Melatonin is the most widely used sleep supplement in the world — sold in virtually every pharmacy, taken by millions every night. But most people take it wrong: too much, at the wrong time, for the wrong problem. Here's what melatonin actually does, when it genuinely helps, and when it won't do anything for your sleep.
What Melatonin Actually Is
Melatonin is a hormone produced by the pineal gland in response to darkness. It doesn't cause sleep — it signals to your brain that it's nighttime. Think of it as a biological clock signal, not a sedative. This distinction is crucial for understanding when melatonin works and when it doesn't.
Your body naturally produces melatonin starting 2-3 hours before your habitual bedtime, peaking in the middle of the night, and declining in the early morning. The entire purpose of this hormone is to communicate "it's dark, it's nighttime" to your circadian system.
When Melatonin Works (and Why)
Jet lag — Strong evidence
Melatonin is most effective for jet lag — the circadian disruption caused by crossing time zones. When you travel east and need to advance your sleep phase (sleep earlier), taking melatonin at the new bedtime helps shift your circadian clock forward. A 2002 Cochrane review of 10 randomized controlled trials found melatonin was effective for preventing and reducing jet lag, particularly for eastward travel across 5+ time zones.
How to use it for jet lag: Take 0.5-5mg at the target bedtime in your new time zone for 3-5 nights after arrival.
Shift work — Moderate evidence
Shift workers who need to sleep during the day can use melatonin to advance their sleep phase. Taking melatonin before daytime sleep helps signal "nighttime" to a circadian system that's receiving conflicting light cues. The evidence is moderate — it helps some shift workers but not all.
Delayed Sleep Phase Disorder (DSPD) — Good evidence
DSPD is a circadian rhythm disorder where the sleep-wake cycle is significantly delayed — people can't fall asleep before 2-3 AM regardless of effort. Low-dose melatonin (0.5mg) taken 5-6 hours before the current natural bedtime can gradually advance the circadian phase. This is one of the most evidence-backed uses of melatonin.
Children with neurodevelopmental conditions — Good evidence
Melatonin has strong evidence for improving sleep in children with autism spectrum disorder, ADHD, and other neurodevelopmental conditions, where circadian rhythm disruption is common. This is one of the most well-supported uses in pediatric sleep medicine.
When Melatonin Doesn't Work
Chronic insomnia — Weak evidence
This is the most important thing to understand: melatonin is not an effective treatment for chronic insomnia. If you can't sleep because of anxiety, racing thoughts, conditioned arousal, or poor sleep hygiene — melatonin won't help. It signals nighttime to your circadian clock; it doesn't address the hyperarousal that causes insomnia.
A 2013 meta-analysis in PLOS ONE found that melatonin reduced sleep onset latency by only 7 minutes and increased total sleep time by 8 minutes in people with insomnia — effects so small they're clinically insignificant. For comparison, CBT-I (Cognitive Behavioral Therapy for Insomnia) reduces sleep onset latency by 30-40 minutes.
General sleep quality improvement — Minimal evidence
If you sleep reasonably well but want "better" sleep, melatonin is unlikely to help. Your body already produces adequate melatonin if your sleep environment is dark and your schedule is consistent. Supplemental melatonin doesn't improve sleep quality in people without circadian rhythm issues.
The Dosage Problem: Why Less Is More
Most melatonin products sold in the US contain 5-10mg per dose. This is 10-20 times higher than the physiologically effective dose. Research consistently shows that 0.5mg is as effective as 5mg for circadian phase shifting — and lower doses produce fewer side effects.
A landmark study by MIT researchers found that 0.3mg of melatonin was the optimal dose for shifting circadian rhythms. Higher doses don't shift the clock more effectively; they just stay in your system longer, potentially causing next-day grogginess.
Recommended doses by use:
- Jet lag / circadian shifting: 0.5-1mg (not 5-10mg)
- DSPD: 0.5mg taken 5-6 hours before current natural bedtime
- General sleep onset: 0.5-3mg, 30-60 minutes before target bedtime
- Children (with medical supervision): 0.5-3mg
Timing Matters More Than Dose
The timing of melatonin is more important than the dose. Taking melatonin at the wrong time can actually delay your circadian phase rather than advance it.
- To fall asleep earlier (advance phase): Take 0.5mg 5-6 hours before your current natural bedtime
- To fall asleep at your target bedtime: Take 0.5-1mg 30-60 minutes before target bedtime
- For jet lag (eastward): Take at the new bedtime for 3-5 nights
- For jet lag (westward): Take in the morning at the destination (counterintuitive but effective)
Side Effects and Safety
Melatonin is generally safe for short-term use. Common side effects at higher doses:
- Next-day drowsiness (most common with high doses)
- Headaches
- Dizziness
- Vivid dreams or nightmares
- Nausea
Long-term safety: The long-term effects of nightly melatonin supplementation are not well-studied. Some research suggests that chronic high-dose melatonin may suppress the body's natural melatonin production. Use the lowest effective dose and consider cycling off periodically.
Drug interactions: Melatonin can interact with blood thinners, immunosuppressants, diabetes medications, and contraceptives. Consult a doctor if you take any medications.
Quality Concerns: What You're Actually Getting
A 2017 study in the Journal of Clinical Sleep Medicine tested 31 melatonin supplements and found that the actual melatonin content ranged from 83% less to 478% more than the labeled dose. Only 8 of 31 products were within 10% of the labeled amount. This means a "3mg" tablet might contain anywhere from 0.5mg to 14mg.
Choose products with third-party testing certification (USP, NSF, or ConsumerLab) to ensure you're getting what the label says.
The Bottom Line
Melatonin works well for what it's designed to do: shift your circadian clock. It's effective for jet lag, shift work, and delayed sleep phase. It's not effective for chronic insomnia, general sleep quality improvement, or falling asleep faster if your circadian rhythm is already aligned.
If you use melatonin, use the lowest effective dose (0.5-1mg), time it correctly, and don't expect it to fix insomnia. For chronic insomnia, CBT-I is the evidence-based treatment.
Is Your Sleep Problem a Circadian Issue or Insomnia?
The answer determines whether melatonin will help. Take our Sleep Quality Assessment to find out what's actually driving your sleep problems.
Sources: Herxheimer & Petrie (2002). Melatonin for the prevention and treatment of jet lag. Cochrane Database. Brzezinski et al. (2005). Effects of exogenous melatonin on sleep. Sleep Medicine Reviews. Erland & Saxena (2017). Melatonin natural health products and supplements. Journal of Clinical Sleep Medicine.