Melatonin is a hormone your body produces naturally to signal that it’s time to sleep. Your brain ramps up production when darkness falls and shuts it down when light hits your eyes, making it the central chemical messenger of your internal clock. But melatonin does more than regulate sleep. It also functions as a powerful antioxidant and plays a role in immune function, which is why it has drawn so much scientific attention beyond its use as a sleep aid.
How Your Body Makes Melatonin
Melatonin is produced in the pineal gland, a pea-sized structure deep in the brain. The process starts with tryptophan, an amino acid you get from food, which gets converted into serotonin and then chemically modified into melatonin. This conversion happens almost entirely during darkness.
The chain of events begins in your eyes. Special light-sensing cells in the retina send signals to a tiny brain region called the suprachiasmatic nucleus, your body’s master clock. When light is present, this clock actively blocks the signal to the pineal gland, and melatonin production stays suppressed. When darkness arrives, the brake lifts. The signal travels from the brain down through the spinal cord and back up through nerve fibers that release a chemical trigger telling the pineal gland to start producing melatonin. This is why bright screens at night can delay melatonin release: the light signal tells your master clock it’s still daytime.
What Melatonin Does for Sleep
Melatonin doesn’t knock you out the way a sedative does. Instead, it tells your brain that the biological night has begun, lowering your core body temperature and promoting the physiological shift toward drowsiness. Think of it as opening the gate to sleep rather than pushing you through it.
As a supplement, melatonin’s effects on sleep are real but modest. A large meta-analysis of clinical trials found that melatonin reduces the time it takes to fall asleep by about 7 to 10 minutes on average. It also slightly increases total sleep duration. These numbers may sound small, but for people who lie awake for long stretches, shaving 10 minutes off that window can be meaningful, especially when combined with other sleep habits.
The dose-response relationship plateaus relatively quickly. A systematic review of randomized controlled trials found that melatonin’s sleep benefits peak at around 4 mg per day, with higher doses offering no additional improvement. Interestingly, taking melatonin about 3 hours before your desired bedtime appears to work better than the more common practice of taking it 30 minutes before bed. The earlier timing gives the hormone more time to shift your internal clock toward sleepiness.
How It Helps With Jet Lag
Jet lag is where melatonin’s benefits are most dramatic. Eight out of ten clinical trials found that melatonin significantly reduced jet lag symptoms for travelers crossing five or more time zones. In one trial, 67% of people on placebo experienced severe jet lag compared to just 17% of those taking melatonin. The estimated number needed to treat is 2, meaning roughly one out of every two people who take it will get a noticeable benefit.
The protocol is straightforward: take 0.5 to 5 mg at bedtime (between 10 p.m. and midnight local time) on the first day of travel after darkness falls, then continue for a few days at the destination. Doses of 0.5 and 5 mg are similarly effective for reducing jet lag overall, though the 5 mg dose helps people fall asleep faster. Quick-release formulations outperform slow-release versions, suggesting a short, sharp spike in melatonin levels works better than a gradual trickle. Taking melatonin before your travel day doesn’t help and isn’t recommended. The benefit tends to be greater the more time zones you cross and is generally more pronounced for eastward flights.
Beyond Sleep: Antioxidant and Immune Effects
Melatonin is one of the body’s more versatile antioxidants. Unlike most antioxidants that neutralize one harmful molecule and are then spent, melatonin triggers a cascade reaction. Both the hormone and its breakdown products can neutralize free radicals, including superoxide anions, hydroxyl radicals, and nitric oxide. One study found melatonin’s antioxidant activity to be roughly three times greater than glutathione (the body’s primary internal antioxidant) and about twice as effective as vitamins C and E. It also crosses barriers that many antioxidants cannot, including the blood-brain barrier, and it directly protects mitochondria, the energy-producing structures inside cells.
On the immune side, melatonin enhances the activity of several types of immune cells. It promotes the proliferation of T cells and B cells (the workhorses of targeted immunity), boosts the killing ability of natural killer cells, and influences how the immune system decides which type of response to mount. There’s a feedback loop at work here: inflammatory signals from the immune system stimulate melatonin production, and melatonin in turn helps calibrate the inflammatory response to keep it from spiraling out of control. This is why researchers have looked at melatonin in the context of conditions involving chronic inflammation, though its clinical applications in this area are still being studied.
Common Side Effects
Melatonin is generally well tolerated, and side effects tend to be mild. The most commonly reported ones are headache, dizziness, nausea, and daytime drowsiness. Less common effects include vivid dreams or nightmares, short-term feelings of depression, irritability, stomach cramps, confusion, and reduced alertness.
If you take blood thinners or anti-platelet medications, melatonin may increase the risk of bleeding. It can also affect blood sugar levels, which matters if you take diabetes medications. Both of these interactions are worth discussing with a healthcare provider before starting melatonin.
Dosage and What’s Actually in the Bottle
Because melatonin is classified as a dietary supplement in the United States, the FDA regulates it far less strictly than prescription or over-the-counter drugs. No official maximum dose has been established through clinical trials, and dosages used in research range from 0.1 mg to 10 mg. Most adults start at 0.5 to 3 mg. In many other countries, melatonin is only available by prescription.
The supplement classification creates a real quality control problem. A 2017 study tested 31 melatonin products from grocery stores and pharmacies and found that most didn’t contain the amount listed on the label. Even more concerning, 26% of the supplements contained serotonin, a hormone that can cause harmful effects even in small amounts. A 2023 study of 25 melatonin gummy products found 22 were inaccurately labeled, with most containing 1.2 to 3.5 times more melatonin than stated. One product contained no detectable melatonin at all. If you use melatonin, choosing products that carry a third-party verification seal can reduce, though not eliminate, this risk.
Melatonin for Children
Melatonin is widely used in children, particularly those with autism or ADHD who often have difficulty falling asleep. The American Academy of Pediatrics advises that it should only be considered after establishing healthy sleep habits first and in consultation with a pediatrician. Starting doses for children are typically low, around 0.5 to 1 mg taken 30 to 90 minutes before bedtime. Most children who benefit, including those with ADHD, don’t need more than 3 to 6 mg. The AAP emphasizes a cautious, carefully monitored approach given the limited long-term safety data in pediatric populations.