For chronic insomnia, the evidence does not support melatonin, and sleep medicine's own guideline recommends against it. That surprises most people, because it is the supplement the whole category is built on. The reason is not that melatonin does nothing. It is that melatonin does something other than what people are buying it for.
What the guidelines say
In 2017 the American Academy of Sleep Medicine published a clinical practice guideline on medications for chronic insomnia in adults. It reviewed each drug and supplement in turn and issued a recommendation for or against.
Melatonin got a recommendation against — for both sleep-onset insomnia and sleep-maintenance insomnia. It was a weak recommendation, which in guideline language means the evidence was low quality and the balance of benefit and burden was unfavorable, not that the substance is dangerous.
The year before, the American College of Physicians had recommended that all adults with chronic insomnia receive CBT-I as the initial treatment, with medication considered only afterwards and only as a shared decision with a clinician.
So the two major guidelines in this area agree: the first thing to try is not a pill or a supplement. It is the behavioral approach.
What melatonin actually does
Melatonin is not a sedative. It is a signal.
Your pineal gland releases it as evening light fades, and the rise tells the rest of the body that night has started. It is the body's way of saying when, not how much. It marks the time; it does not push you under.
That distinction explains most of the confusion. Someone whose problem is that their body clock is running late — a teenager who cannot fall asleep before 2am and cannot wake before 11, or a traveller five time zones from home — has a timing problem, and a timing signal can help. Someone who is in bed at a reasonable hour, tired, and lying awake because their mind will not stop has a different problem entirely, and no amount of clock signal addresses it.
Where melatonin does have a role
- Jet lag. Shifting the clock deliberately after crossing time zones is what it is good at.
- Delayed sleep-wake phase disorder. A body clock genuinely running hours late, most commonly in adolescents and young adults.
- Some shift-work schedules, under guidance, where the aim is to move the clock rather than to sedate.
In each of those, timing and dose matter more than most people realise — taken at the wrong hour it can shift the clock the wrong way. That is a conversation with a clinician, not a guess.
The size of the effect
Pooled analyses of melatonin trials find it shortens the time taken to fall asleep by roughly seven minutes on average, and increases total sleep time by a similarly modest amount.
Seven minutes is a real effect. It is also not what somebody lying awake for ninety minutes is looking for. And for comparison, the meta-analysis behind the CBT-I guidelines found the behavioral approach producing changes several times that size in the same measures — with the difference that those improvements were still there a year later, because what changed was behavior rather than chemistry.