Sleep glossary
Melatonin
What melatonin actually does in the body, why it works as a timing signal rather than a sedative, and where the supplement question belongs.
In short
Melatonin is the hormone your brain releases in the evening to signal biological night. It does not knock you out, it tells the rest of your body what time it is, and light in the evening delays its release.
Melatonin is also called sleep hormone, dim light melatonin onset or DLMO.
The pineal gland releases it, and the release is controlled by the same master clock that runs your circadian rhythm. Levels stay low through the day, begin climbing in the evening, peak somewhere in the middle of the night and fall away before you wake. Researchers call that evening rise the dim light melatonin onset, and it is one of the cleanest markers available for where a person’s body clock actually sits.
The word people get wrong is sedative. Melatonin is a message, not an off switch. It tells your body that biological night has started, and the body responds by lowering core temperature, easing alertness and letting the wake maintenance zone release its grip. That is why the timing of the signal matters more than the size of it.
Light is the volume knob
Light reaching the eye suppresses melatonin, and the effect depends on intensity, duration and time of day. Evening light delays the rise. Morning light does the opposite to the clock as a whole, advancing it. This is the mechanism behind most practical advice about blue light in the evening, though brightness and timing generally do more work than colour temperature alone. Turning the room down is more effective than turning one screen orange.
Two things follow. First, a late chronotype usually has a late melatonin onset, so an early bedtime is asking the body to sleep before the signal has arrived. Second, if you want to move that signal, the lever is light at consistent times, which is exactly what how to fix your sleep schedule works through.
On supplements: they are regulated differently from country to country, timing and amount both matter, and they can interact with medication and with existing conditions. That makes them a conversation with a doctor or pharmacist, not something an app should advise on. Tock is not a medical device, and persistent trouble sleeping is worth raising with a clinician rather than self managing indefinitely.
Questions people ask
Does melatonin make you fall asleep?
Not the way a sedative does. Melatonin is a timing signal that tells your body it is biological night. Whether a supplement helps you, and when or how much, is a question for a doctor or pharmacist rather than an app.
Does evening screen light really affect melatonin?
Light in the evening can delay melatonin release, and brightness and timing matter at least as much as colour. Dimming the whole room in the hour before bed is a more reliable lever than any single screen setting.