Melatonin Side Effects: What You Need to Know Before Taking It
When you’re struggling to fall asleep, melatonin, a natural hormone your brain makes to signal it’s time to sleep. Also known as the sleep hormone, it’s one of the most popular over-the-counter sleep aids in the U.S. But just because it’s available without a prescription doesn’t mean it’s harmless. Many people take it without knowing how it affects their body beyond helping them nod off. The truth? Melatonin can cause real side effects—even at low doses—and those effects vary wildly from person to person.
One of the most common issues is next-day grogginess. Unlike some sleep pills that knock you out and leave you foggy for hours, melatonin doesn’t always work that way. But if you take it too late, take too much, or your body metabolizes it slowly, you might wake up feeling like you ran a marathon. Dizziness, headaches, and mild nausea show up in studies of people using even 0.5 mg to 5 mg. And while it’s often marketed as safe for long-term use, there’s little solid data on what happens after months or years of daily use. Some research suggests it might interfere with natural melatonin production over time, making your body rely on the supplement just to fall asleep.
It’s not just about dosage. Timing matters just as much. If you’re dealing with circadian rhythm, your body’s internal clock that controls when you feel awake or tired disorders like jet lag or delayed sleep phase, melatonin can help reset your schedule. But if you take it at the wrong time—say, right after dinner instead of 1–2 hours before bed—it can throw your rhythm off even more. And if you’re on other meds? Watch out. Melatonin can interact with blood thinners, diabetes drugs, and even some antidepressants. It’s also not recommended for pregnant women, people with autoimmune diseases, or those with seizure disorders.
What’s surprising is how often people ignore the signs. If you’re waking up with vivid dreams, feeling unusually moody, or getting unexplained muscle aches, melatonin could be the culprit. Most users assume these are just "normal" side effects and keep taking it. But they’re not. Your body is trying to tell you something. The good news? Many of these effects fade once you stop or lower the dose. And for some, switching to a lower dose—like 0.3 mg instead of 3 mg—makes all the difference.
There’s also a big gap between what’s sold and what’s actually in the bottle. Independent tests have found some melatonin supplements contain up to 470% more than the label claims. Others have contaminants like serotonin or even prescription sedatives. That’s why sticking to reputable brands and checking third-party certifications matters more than you think.
And then there’s the bigger picture: melatonin isn’t a fix for poor sleep habits. If you’re scrolling in bed at midnight, drinking coffee after 3 p.m., or sleeping in on weekends, no amount of melatonin will fix that. It’s a signal, not a solution. The best results come when you pair it with consistent sleep routines, dark bedrooms, and avoiding screens before bed.
Below, you’ll find real-world insights from people who’ve dealt with melatonin side effects, what the research actually says about long-term use, and how to tell if it’s helping—or hurting—your sleep. You’ll also see how it connects to other sleep issues, from jet lag to shift work, and why some people swear by it while others feel worse after taking it.
