What Is Melatonin? The Body’s Natural Sleep Hormone

Melatonin is a hormone produced by the brain in response to darkness. It helps regulate the body’s internal clock, or circadian rhythm, and signals that it is time to sleep.

At a glance

Term: Melatonin
What it is: Hormone
Section: Sleep
In one line: It’s the hormone your body makes to tell you it’s getting dark and time to wind down for bed.

What Melatonin means

Melatonin is a hormone that your brain’s pineal gland produces naturally, primarily to regulate your sleep-wake cycle. Its main job is to manage your internal body clock, also known as your circadian rhythm. Production of melatonin increases in the evening as natural light fades, which sends a signal to your body that it’s time to wind down and prepare for sleep. As you sleep, levels stay elevated. Then, in the morning, exposure to light signals the brain to decrease production, helping you wake up and feel alert for the day.

This hormone acts as the body’s timekeeper, synchronizing your internal schedule with the 24-hour day-night cycle. This affects not just sleep, but also other bodily functions like body temperature and blood pressure. Modern life can disrupt this natural process. For example, exposure to blue light from screens in the evening can suppress melatonin production, making it harder to fall asleep. Similarly, things like jet lag or working night shifts can confuse your body’s melatonin signals, throwing your entire sleep schedule off balance.

Because of its role in sleep, melatonin is also sold as an over-the-counter dietary supplement. People often use it for short-term sleep issues like adjusting to a new time zone or managing sleep difficulties related to shift work. In the United States, supplements are not regulated by the Food and Drug Administration (FDA) with the same rigor as prescription drugs. This means the dose and purity of ingredients listed on the label may not always be accurate. It’s generally intended for occasional, short-term use rather than as a nightly sleep aid.

Melatonin is not a sedative or a traditional sleeping pill that forces your brain to shut down. Instead, it works by adjusting your body clock, gently nudging your body toward sleep. Its effectiveness can vary widely among individuals, and taking it at the wrong time or in the wrong amount can sometimes interfere with your natural sleep cycle. It is not a substitute for good sleep hygiene and may not address underlying medical conditions that can cause sleep problems.

What public guidance says

The CDC recommends that adults get 7 or more hours of sleep per night on a regular basis.

How melatonin works

Darkness signals production. When your eyes detect darkness, they send a signal to your brain, which then instructs the pineal gland to start producing melatonin.
Levels rise in the evening. As melatonin levels in your bloodstream increase, you typically begin to feel less alert and more sleepy.
Levels peak overnight. Melatonin levels generally stay elevated through the night, helping to maintain a state of sleep.
Light signals a stop. When your eyes are exposed to light in the morning, the pineal gland is instructed to stop producing melatonin, which helps you wake up.

Melatonin vs. similar terms

Compared with	How Melatonin differs	What the other term means
Serotonin	Melatonin is a hormone primarily involved in regulating the sleep-wake cycle.	Serotonin is a neurotransmitter that affects mood, appetite, and digestion, and is also a precursor from which melatonin is made.

Common misconceptions

Myth: Melatonin is a sedative that knocks you out. Melatonin is a chronobiotic, meaning it helps regulate the timing of your sleep. It signals to your body that it’s nighttime but doesn’t induce sleep through sedation.
Myth: The more melatonin you take, the better you’ll sleep. Higher doses are not necessarily more effective and can increase the risk of side effects like grogginess or headaches. The goal is to mimic the body’s low natural levels.
Myth: Since it’s ‘natural,’ taking melatonin is always safe. Melatonin is a hormone, and taking it as a supplement can have side effects and interact with medications. As a supplement, its purity and dosage are not strictly regulated by the FDA.

Related terms

When to bring in a professional

It’s a good idea to speak with a doctor or pharmacist if you have persistent sleep problems or are thinking about taking supplements.

You have trouble falling or staying asleep for more than a few weeks.
You suspect an underlying sleep disorder, such as insomnia or sleep apnea.
You are considering taking melatonin and want to discuss dosage, timing, and potential interactions with other medications.
You experience side effects like daytime grogginess, dizziness, or headaches after taking melatonin.

How this entry was made: drafted with AI assistance from general, widely published definitions, checked in a separate verification pass for invented numbers and claims, and edited by the Millennials Wellness editors. General information only, not medical, financial or legal advice. Last checked October 2026. Our ground rules · Back to the glossary