Maybe, a little. Several studies have found that people sleep somewhat less and fall asleep later around the full moon, by roughly twenty minutes in one well-known laboratory study and by more in the nights before the full moon in a field study. But other large studies have found no effect at all, so the honest answer is that the evidence is mixed, and any effect is small next to caffeine, stress, screens and a noisy street.
The study that started the modern debate
In 2013, a team at the University of Basel led by Christian Cajochen published a short paper in Current Biology with the title "Evidence that the lunar cycle influences human sleep." They hadn't set out to study the Moon. They went back to sleep recordings from 33 volunteers who had spent nights in a windowless lab for other research, with no clocks and no view of the sky, and sorted the nights by moon phase afterwards.
Around the full moon, they reported:
- deep-sleep brain activity, measured by EEG, was down by about 30 percent
- volunteers took about five minutes longer to fall asleep
- they slept about twenty minutes less in total
- they rated their sleep as worse, and their melatonin levels were lower
Because the lab had no windows, moonlight couldn't explain the results. The authors suggested the possibility of an internal "circalunar" rhythm, a body clock tuned to the lunar cycle, like those well documented in many marine animals. The paper got a great deal of press, and it made a long-dismissed idea respectable to test again.
Then the replications
Science works by checking, and over the next few years several groups looked at their own data.
No effect in a large re-analysis. In 2014, a team including Maren Cordi and Martin Dresler pooled existing sleep datasets and analyzed sleep data from more than 1,200 volunteers across roughly 2,000 nights and found no meaningful link with moon phase. They also raised the "file drawer problem": studies that find nothing tend not to get published, so a few positive results can look more convincing than they are.
Support from Sweden. The same year, a group at the University of Gothenburg re-analyzed data from 47 healthy young adults originally collected for a study on noise. They found shorter sleep and higher brain reactivity around the full moon, with the sleep differences reported mainly in the men.
Support from a sleep clinic. A Hungarian study of 319 patients referred for sleep testing found lower sleep efficiency and less deep sleep on full moon nights than on new moon nights.
No effect in the general population. In 2015, a Swiss study of 2,125 adults who had their sleep recorded at home found no significant differences across moon phases in how well people slept, how long they slept, or their stress hormone levels. The authors put their conclusion right in the title: don't blame the moon.
A tiny effect in children. A 2016 study of 5,812 children aged nine to eleven in twelve countries found they slept about five minutes less around the full moon than around the new moon. The authors themselves questioned whether a difference that small matters in daily life.
The field study with wrist monitors
The most interesting recent work moved out of the lab. In 2021, a team led by Leandro Casiraghi and Horacio de la Iglesia at the University of Washington published a study in Science Advances that followed people in real life with wrist activity monitors.
They tracked Toba/Qom communities in northern Argentina, some living with no electricity, some with limited access and some in a town, along with hundreds of college students in Seattle. Across all these groups, people went to sleep later and slept less on the nights before the full moon, with the strongest effect a few nights ahead of it.
That timing is a clue. In the days before full moon, the waxing Moon is already high and bright in the early evening, when people are still awake and choosing whether to stay up. After the full moon, the Moon rises later in the night, when most people are already asleep. The researchers suggested that moonlight in the evening once offered extra hours of usable light, and that people may have evolved to make use of them. Surprisingly, the effect also showed up in the city, where artificial light should have swamped any moonlight, which leaves the mechanism an open question.
Why the results disagree
Put together, these studies point in different directions, and there are good reasons why:
- Most were retrospective. They re-analyzed data collected for other purposes. That's efficient, but it makes chance findings more likely, especially in small groups.
- Small samples. Thirty or forty sleepers is a small number to detect a twenty-minute effect reliably.
- Publication bias. A surprising positive result is more likely to be published than a dull null result, which skews the visible record.
- Different definitions. Studies drew the "full moon" window differently, from one night to several, and compared it against different baselines.
- Different settings. A windowless lab, a home bedroom and a village without electricity are very different places to look for a moonlight effect.
What doesn't hold up is the idea that the Moon's gravity tugs on your body the way it pulls the oceans. Tides depend on the size of a body of water; across something the size of a person, the Moon's tidal effect is vanishingly small.
If you sleep badly around the full moon
Whether the cause is moonlight, expectation or coincidence, a bad night is a bad night. A few things are worth trying:
- Keep a short sleep diary for two lunar cycles. Note bedtime, wake time and how rested you feel, and mark the moon phase from our moon phase today page. Many people find the pattern they expected isn't there; some find it is.
- Make the room properly dark. If moonlight comes in through a gap in the curtains, blackout blinds or a sleep mask fix it.
- Hold your wake-up time steady, even after a short night. It's the most reliable anchor for your body clock.
- Watch the usual suspects first: late caffeine, alcohol, screens in bed and a too-warm room.
- Talk to a doctor if you're regularly sleeping badly for weeks at a time, whatever the Moon is doing.
If you enjoy the full moon, there's no reason to fight it, either. A short walk under it and a few minutes of reflection, as in our full moon ritual, can make it a pleasant night rather than a dreaded one. Dates for upcoming full moons are on our full moon calendar.
Questions readers ask
Is it the moonlight that keeps people awake?
That's the leading idea for real-world effects, especially in the evenings before the full moon when the Moon is bright and already up. But some lab studies reported effects in rooms with no windows, which light can't explain. Whether those findings reflect an inner rhythm or chance is still debated.
Does the full moon affect children's sleep?
A large twelve-country study of nine to eleven year olds found they slept about five minutes less around the full moon. That's statistically detectable but very small, and the researchers doubted it makes a practical difference.
Why do I feel restless at the full moon?
It could be extra light, a few minutes' less sleep, or simple expectation: if you believe the full moon disrupts sleep, you're more likely to notice and remember a bad night that falls on one. A sleep diary is the best way to find out which applies to you.
Does the Moon affect mood as well as sleep?
Large studies of mood, emergency visits and psychiatric admissions have mostly found no effect. Sleep is the most plausible link where effects do appear. We look at the evidence in does the moon affect your mood, and for the astronomy behind the cycle, see the Moon's phases explained.
