For most adults, melatonin is considered appropriate for 1 to 13 weeks of use, depending on the sleep problem. Beyond that window, the evidence on safety thins out considerably, and some recent data raises concerns about prolonged supplementation. Here’s what the current guidelines and research actually say about duration.
Recommended Duration for Adults
The NHS, which regulates melatonin as a prescription medicine, recommends a maximum of 13 weeks for short-term sleep problems in adults. Most people are advised to take it for just 1 to 4 weeks. For jet lag specifically, the recommended limit is 5 days.
If your sleep problems persist beyond 13 weeks, that doesn’t necessarily mean you should keep taking melatonin on your own. It typically means a sleep specialist should evaluate what’s driving your insomnia. They may prescribe melatonin for longer periods, but that decision involves monitoring and follow-up. The American Academy of Sleep Medicine actually recommends against using melatonin as a treatment for chronic insomnia in adults, suggesting it’s not the right tool for ongoing sleep difficulties.
Does Melatonin Stop Working Over Time?
One reason people wonder about duration is the fear of building tolerance, the way you might with other sleep aids. On this front, the news is relatively reassuring. Animal research has shown that after 14 days of continuous melatonin exposure at pharmacological doses, the brain cells responsible for regulating your sleep-wake cycle remained just as responsive to melatonin as before treatment. The receptors didn’t become desensitized.
This suggests melatonin works differently from many sleep medications, where you need progressively higher doses to get the same effect. That said, 14 days in a lab is a far cry from months or years of nightly use in humans, and tolerance studies over longer periods are lacking.
What Happens With Long-Term Use
This is where things get more complicated. A large study published through the American Heart Association tracked over 65,000 adults with insomnia who used melatonin for at least a year, comparing them to matched controls who didn’t use it. Over five years of follow-up, the melatonin group had an 89% higher rate of developing heart failure, roughly triple the rate of heart failure-related hospitalizations, and double the rate of death from any cause compared to the control group.
These are striking numbers, but they come with important caveats. This was an observational study, not a clinical trial. People who take melatonin every night for years may differ from non-users in ways that are hard to fully account for, even after matching on more than 40 baseline variables. It’s also possible that the underlying insomnia itself, rather than the melatonin, contributes to cardiovascular risk. Still, this is the kind of signal that makes researchers and clinicians cautious about endorsing indefinite use.
Risks for Older Adults
Adults over 65 face additional considerations. Melatonin has a blood pressure-lowering effect, which can interact unpredictably with common medications for hypertension. It can also amplify the sedating effects of other medications, including antidepressants. For people taking blood thinners like warfarin, melatonin may increase bleeding risk by affecting clotting time.
European and American guidelines recommend that older adults stick to the lowest effective dose, generally no more than 1 to 2 mg, taken 30 to 60 minutes before bed. The overall safety profile appears favorable in the short term for this age group, but there is very little evidence on what happens with prolonged use. If you’re over 65 and taking melatonin regularly, it’s worth discussing your other medications with a pharmacist or doctor to check for interactions.
Children and Adolescents
Pediatric sleep experts are particularly cautious about duration. The International Pediatric Sleep Association recommends that melatonin be used for as short a period as possible in typically developing children, with long-term use (more than 3 to 6 months) considered inappropriate for the vast majority.
The concern unique to children involves puberty. Natural melatonin levels gradually decline as puberty approaches, and there is some evidence that prolonged supplementation, particularly beyond 7 years, may delay pubertal development. Experts recommend regular follow-up appointments to reassess whether a child still needs melatonin, along with periodic “drug holidays” where the supplement is paused to see if the sleep problem has resolved on its own.
A Practical Approach to Duration
If you’re using melatonin to reset your sleep schedule after travel, a shift change, or a rough patch, a few days to a few weeks is well within the evidence-supported range. The key is treating it as a short-term tool rather than a permanent fixture on your nightstand.
If you find yourself reaching for melatonin every night for months, that’s a signal worth paying attention to. It likely means something else is disrupting your sleep, whether that’s a habit (screens, irregular bedtimes, caffeine timing), an underlying condition like sleep apnea, or stress and anxiety. Cognitive behavioral therapy for insomnia, often called CBT-I, is considered the first-line treatment for chronic sleep problems and has lasting effects without ongoing supplementation.
One practical note that applies regardless of duration: in the United States, melatonin is sold as a dietary supplement, which means it’s not regulated the same way as medication. Independent testing has found that the actual melatonin content in supplements can vary dramatically from what’s listed on the label. If you’re taking melatonin in a country where it’s available over the counter, look for products that carry a third-party verification seal.