A 15 mg dose of melatonin is three times higher than the typically recommended maximum of 5 mg for adults, and well above the 2 to 3 mg doses used in most clinical settings. It’s unlikely to cause a medical emergency in a healthy adult on a single occasion, but it’s not a dose supported by good safety data, and it comes with a higher risk of side effects and drug interactions than lower amounts.
How 15 mg Compares to Standard Doses
The NHS prescribes melatonin as a 2 mg slow-release tablet for short-term insomnia, with a maximum of 10 mg for longer-term sleep problems. For jet lag, the typical dose is 3 mg, with an upper end of 6 mg. The Mayo Clinic describes the “typically recommended maximum” as 5 mg or fewer. By any of these benchmarks, 15 mg sits well outside normal therapeutic range.
Your body produces a tiny amount of melatonin naturally each evening, roughly 0.1 to 0.3 mg worth in circulation. Even a 1 mg supplement raises blood levels far above what your brain would produce on its own. At 15 mg, you’re flooding your system with a hormone signal that’s orders of magnitude beyond what your pineal gland ever intended.
What a High Dose Feels Like
Melatonin is absorbed quickly, with a half-life of only 20 to 50 minutes. That means your body clears half the dose within an hour. But at 15 mg, even after several half-lives, you still have more melatonin circulating than a standard dose would provide at its peak. The practical result: you may feel groggy, foggy, or “hungover” well into the next morning. Other common side effects at higher doses include headaches, dizziness, nausea, and daytime drowsiness that defeats the purpose of taking it in the first place.
Some people also experience vivid or disturbing dreams at higher doses. Because melatonin influences your sleep architecture, not just the timing of sleep onset, taking more than you need can change how you cycle through sleep stages in ways that leave you feeling less rested, not more.
More Is Not More Effective
This is the counterintuitive part. Melatonin works as a timing signal, not a sedative. Its job is to tell your brain that it’s nighttime. Once you’ve sent that signal, amplifying it doesn’t make you fall asleep faster or stay asleep longer. Research consistently shows that doses in the 0.5 to 3 mg range are effective for shifting sleep timing, and that higher doses don’t produce better sleep outcomes. If 3 mg isn’t working for you, 15 mg is unlikely to solve the problem, because the issue probably isn’t a melatonin deficiency.
Drug Interactions Get Riskier at Higher Doses
Melatonin interacts with several categories of medication, and those interactions become more significant as the dose increases. If you take blood pressure medication, melatonin can worsen blood pressure control. If you use blood thinners or anti-platelet drugs, melatonin may increase bleeding risk. For people on seizure medications, it can reduce those drugs’ effectiveness. Diabetes medications, sedatives, and other central nervous system depressants also interact with melatonin, with sedatives in particular producing a compounding drowsiness effect.
At 2 or 3 mg, these interactions exist but are relatively mild. At 15 mg, you’re increasing the stakes without any corresponding benefit to your sleep.
You May Not Be Getting 15 mg Anyway
In the United States, melatonin is classified as a dietary supplement, which means it faces far less manufacturing oversight than prescription or over-the-counter drugs. The actual melatonin content in supplements is notoriously unreliable. A 2017 study analyzed 31 supplements and found that more than 71 percent didn’t contain within 10 percent of what the label claimed. The actual content ranged from 83 percent less to 478 percent more than labeled. Lot-to-lot variability within a single product was as high as 465 percent.
A 2023 study of melatonin gummies found similar problems: 22 out of 25 products were inaccurately labeled, with melatonin levels ranging from 74 to 347 percent of the stated amount. One product contained no detectable melatonin at all. So a bottle labeled 15 mg could deliver anywhere from a few milligrams to over 50 mg per dose. That 2017 study also found serotonin, a completely different neurotransmitter, in 26 percent of tested supplements, at potentially significant doses.
Long-term Safety Is Unknown
The National Center for Complementary and Integrative Health states plainly that for melatonin doses higher than what the body normally produces, “there’s not enough information yet about possible side effects to have a clear picture of overall safety.” Short-term use at standard doses appears safe for most adults, but long-term, high-dose use hasn’t been adequately studied.
One reassuring finding: supplemental melatonin does not appear to suppress your body’s natural melatonin production. Studies lasting up to 12 months found no withdrawal symptoms and no reduction in the body’s own melatonin output after stopping. So if you’ve been taking 15 mg and want to stop or reduce your dose, you’re unlikely to experience rebound insomnia from a hormonal standpoint.
A Better Approach Than 15 mg
If you’ve landed on 15 mg because lower doses weren’t working, the dose itself probably isn’t the problem. Sleep difficulties that don’t respond to 1 to 3 mg of melatonin usually have underlying causes that melatonin can’t fix: stress, inconsistent sleep schedules, screen exposure before bed, sleep apnea, or other medical conditions.
Try starting at 0.5 to 1 mg, taken one to two hours before your target bedtime. If that does nothing after a week, increasing to 3 mg is reasonable. Beyond 5 mg, you’re in territory where side effects increase but benefits plateau. If you’re currently taking 15 mg and sleeping fine, you’d likely sleep just as well at a fraction of that dose, with fewer side effects and less morning grogginess.