Have you ever tossed and turned under a full moon and wondered if its glow was keeping you awake? For generations, the Moon was believed to have the power to cause sleepless nights and strange behavior, even madness itself. In fact, the word madness comes directly from luna, which is Latin for “moon.”
Police, hospital and emergency personnel often report that their nights become more restless during a full moon. But does science confirm it?
The answer, of course, is more nuanced than tradition suggests. Research shows that the full moon can slightly affect sleep, although its influence on mental health is much less certain.
I am a neurologist specialized in sleep medicine and I study how sleep influences brain health. I find it fascinating that an ancient myth about moonlight and madness could have its origins in something much more common: our restless sleep under its glow.
The real effect of the full moon when sleeping
Several studies show that people sleep differently in the days before the full moon, when its light shines brightest in the night sky. During this period, you sleep about 20 minutes less, it takes longer to fall asleep and you enjoy less time in deep, restful sleep.
Large-scale population studies confirm this pattern, finding that people from different cultures tend to go to bed later and sleep less in the nights before the full moon.
The most likely explanation is light. A bright moon at dusk can slow the body’s internal clock, reduce the production of melatonin—the hormone that signals bedtime—and keep the brain more alert. The changes are slight—most people lose only 15 to 30 minutes of sleep—but the effect is measurable. This impact is stronger in places without artificial light, such as rural areas or when camping.
Some research also suggests differences between men and women. For example, men seem to lose more sleep during the waxing phase, while women experience slightly less deep, restful rest around the full moon.
The link with mental health
For centuries, the full moon has been blamed for causing madness. Folklore held that its brightness could trigger mania in people with bipolar disorder, seizures in those suffering from epilepsy, or psychosis in patients with schizophrenia. The theory was simple: if moonlight disrupts sleep, the most vulnerable minds could become destabilized.
Modern science offers an important nuance. Today it is known that lack of sleep in itself is a powerful trigger of mental health problems. Even a single night of poor sleep can increase anxiety and depress mood. Chronic sleep disruption increases the risk of depression, suicidal thoughts, and episodes of disorders such as bipolar or schizophrenia.
This means that even if sleep loss during a full moon is mild, it could be significant for the most vulnerable people. Someone with bipolar disorder, for example, might be much more sensitive to shortened or fragmented sleep than the average person.
However, when researchers analyze large population groups, the evidence that moon phases cause psychiatric crises is weak. No reliable pattern has been found between the Moon and hospital admissions, discharges, or length of stay.
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Still, some studies point to possible minor effects. In India, psychiatric hospitals saw increased use of restraints during full moons, based on data from 2016 and 2017. In China, researchers noted a slight increase in schizophrenia admissions around the full moon, based on hospital records from 2012 to 2017.
However, these findings are not uniform globally and could reflect cultural factors or local hospital practices as much as biological causes.
In summary, the Moon can slightly reduce our sleep time, and lack of sleep undoubtedly affects mental health, especially in vulnerable people: those suffering from depression, bipolar disorder, schizophrenia or epilepsy, as well as adolescents sensitive to interruptions in rest. However, the idea that the full moon directly causes waves of psychiatric illness remains more myth than reality.
Other theories that do not convince
Over the years, scientists have explored other possible explanations for the supposed lunar effects: from the gravitational pull of the tides on the body to geomagnetic changes or variations in barometric pressure. However, none of these mechanisms stand up to rigorous analysis.
The gravitational forces that move the oceans are too weak to affect human physiology, and studies on geomagnetic and atmospheric changes during lunar phases have yielded inconsistent or insignificant results. This makes sleep disruption from nighttime light exposure the most plausible link between the Moon and human behavior.
Why does the myth persist?
If science is so inconclusive, why do so many people believe in the “full moon effect”? Psychologists point to a phenomenon called illusory correlation: We tend to notice and remember the unusual nights that coincide with the full moon, but we forget the many when nothing special happens.
Furthermore, the Moon is a visible and obvious object. Unlike invisible factors that disrupt sleep—like stress, caffeine, or excessive phone use—the Moon is right there in the sky, ready to be blamed.
Lessons from the Moon for the ‘modern’ dream
Although the Moon does not drive us “crazy,” its small influence on sleep highlights something important: night light matters.
Our bodies are designed to follow the natural cycle of light and dark. Excess light at dusk—whether from the moon, streetlights, or cell phone screens—can delay circadian rhythms, reduce melatonin, and cause lighter, more fragmented sleep.
This same biology helps explain the risks of daylight saving time. When the clocks go forward, the nights remain artificially brighter. This change delays sleep and disrupts the circadian rhythm on a much larger scale than the Moon, contributing to an increase in accidents, cardiovascular problems, and reduced job security.
In the modern world, artificial light has a much greater impact on sleep than the Moon itself. For this reason, many sleep experts advocate maintaining a permanent standard schedule, more in line with our biological rhythms.
So if you feel restless on a full moon night, it may not be entirely your imagination: the Moon can affect your rest a little. But if you suffer from insomnia frequently, take a better look at your surroundings. The fault probably lies in the light you hold in your hand, not the one shining in the sky.
*Joanna Fong-Isariyawongse is Associate Professor of Neurology, University of Pittsburgh
This article was originally published in The Conversation
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