Taking melatonin supplements raises the level of a hormone your brain already produces naturally, signaling to your body that it’s time to sleep. Most people take it to fall asleep faster, adjust to a new time zone, or reset a disrupted sleep schedule. But melatonin does more than just make you drowsy. It influences which stages of sleep you spend time in, acts as an antioxidant, and interacts with your immune system in ways researchers are still mapping out.
How Melatonin Works in Your Brain
Your pineal gland, a tiny structure deep in your brain, releases melatonin when it gets dark. Under a normal schedule, melatonin secretion starts rising about two hours before your usual bedtime, peaks around 3 to 4 a.m., and stays elevated for roughly 12 hours overnight. Light suppresses it during the day. When you swallow a melatonin supplement, you’re adding to that natural signal or, in many cases, providing it at a time your body hasn’t started producing it yet.
Melatonin works by binding to two specific receptors in the brain, called MT1 and MT2. These receptors do different things. MT1 receptors sit in brain areas that control REM sleep (the phase where dreaming happens) and help regulate your circadian clock. MT2 receptors are concentrated in a region called the reticular thalamus and primarily promote non-REM sleep, the deeper, more restorative phases. Together, these receptors quiet down brain activity by reducing stimulating chemical signals inside your cells, essentially telling your nervous system to wind down.
What It Does for Sleep
The most immediate effect you’ll notice is feeling sleepy 30 to 90 minutes after taking it. Melatonin doesn’t knock you out the way a sedative does. Instead, it opens what sleep researchers call a “sleep gate,” making it easier to drift off if you’re in a dark, calm environment. It’s most useful when your internal clock is out of sync with when you need to sleep.
One well-documented effect is that melatonin increases the amount of time you spend in REM sleep. It does this partly by triggering the release of a protein called vasotocin, which regulates REM cycles. More REM sleep means more dreaming, and many people report noticeably vivid or strange dreams after taking melatonin. For some, those dreams tip into unpleasant territory.
Jet Lag and Shift Work
Melatonin is particularly effective for jet lag. The American Academy of Sleep Medicine lists timed melatonin as a standard treatment for frequent travelers. The trick is timing: if you take it when your internal clock thinks it’s early evening, it shifts your sleep schedule earlier, which helps after eastward travel. Taking it when your body thinks it’s morning shifts your schedule later, useful after flying west.
For jet lag, doses as low as 0.5 to 1 mg are often enough to produce a circadian shift. The CDC specifically cautions against taking more than 5 mg for jet lag because excess melatonin lingers in your system and can end up active at the wrong time of day, potentially making the adjustment harder. Once you arrive at your destination, take your first dose at your new local bedtime, ideally between 8 p.m. and 4 a.m.
Beyond Sleep: Antioxidant and Immune Effects
Melatonin is also one of your body’s built-in antioxidants. It directly neutralizes free radicals, the unstable molecules that damage cells, and it activates several of your body’s own antioxidant defense systems. This protective effect extends to every organ, not just the brain.
Its relationship with inflammation is more nuanced than a simple on/off switch. During the early stages of inflammation, when your body needs an immune response to deal with an injury or infection, melatonin actually supports that inflammatory process. But during chronic, lingering inflammation, it shifts to an anti-inflammatory role, dialing down the chemical signals that keep inflammation going. A meta-analysis of clinical trials found that melatonin significantly reduced several key inflammatory markers, including multiple interleukins and tumor necrosis factor. These effects are still being studied in clinical settings, but they help explain why melatonin research extends well beyond sleep.
Common Side Effects
Most people tolerate melatonin well, but side effects do happen. The most common ones are headaches, dizziness, nausea, and next-day drowsiness. Less common effects include temporary feelings of depression, mild anxiety, abdominal cramps, irritability, reduced alertness, and low blood pressure. The vivid dreams mentioned earlier are frequent enough that many users consider them a defining feature of taking melatonin rather than a side effect.
Next-morning grogginess is often a sign you took too much or took it too late. Experts generally suggest 1 to 3 mg per night for adults, taken one to two hours before bed. Higher doses don’t necessarily work better and are more likely to leave you foggy the next day.
The Label Accuracy Problem
Because melatonin is sold as a dietary supplement in the United States, it isn’t regulated the way prescription drugs are. This creates a real quality control issue. A study published in JAMA analyzed 25 melatonin gummy products and found that 22 of them (88%) were inaccurately labeled. The actual melatonin content ranged from 74% to 347% of what the label claimed. Some products also contained substances not listed on the label, including serotonin and CBD. This means you could be taking more than triple the dose you intended without knowing it.
If accuracy matters to you, look for products that carry a third-party testing seal from organizations like USP or NSF International. These certifications verify that what’s on the label matches what’s in the bottle.
Drug Interactions to Be Aware Of
Melatonin can interact with several types of medication. It may increase the risk of bleeding when combined with blood thinners or anti-platelet drugs. It can worsen blood pressure in people already taking blood pressure medication. Combining it with other sedating substances, including alcohol, amplifies drowsiness. It may also interfere with seizure medications, particularly in children with neurological conditions, and it can affect blood sugar control in people taking diabetes medication. If you’re on any of these, it’s worth checking with a pharmacist before adding melatonin.
Melatonin and Children
Melatonin use in children has grown rapidly, and so have accidental ingestion reports. Between 2012 and 2021, poison control centers received more than 260,000 reports involving children and melatonin. Most cases resolved without symptoms, but some required hospitalization, and two children died. The label inaccuracy problem makes this especially concerning for pediatric use, since a product containing far more melatonin than advertised poses a greater risk to a smaller body.
The American Academy of Pediatrics recommends starting children at the lowest possible dose, typically 0.5 to 1 mg, taken 30 to 90 minutes before bed. Most children who benefit don’t need more than 3 to 6 mg, including those with ADHD. The AAP also emphasizes that melatonin should come after establishing good sleep habits, not as a replacement for them. Long-term safety data in children is limited, and there are unresolved concerns about potential effects on growth and puberty.
What We Know About Long-Term Use
Short-term melatonin use is considered generally safe. Long-term nightly use is where the picture gets less clear. There simply isn’t robust data tracking what happens when adults take melatonin every night for years. Unlike some sleep medications, melatonin doesn’t appear to create physical dependence, and stopping it doesn’t cause withdrawal symptoms. But the absence of long-term safety data isn’t the same as proof of long-term safety. If you’ve been taking it nightly for months, periodically reassessing whether you still need it is a reasonable approach.