Do Full Moons Make People Act Crazy? The Lunar Effect, Explained
Urban legends abound on the subject of things, and people, going haywire around the time of the full Moon. But is there any truth to it? Depends on who you ask.
Quick Reference: Full Moon Behavior at a Glance
- The claim: the full Moon makes people act strangely; ERs, vet clinics, and police see more action; sleep gets worse; babies arrive.
- Where the word comes from: “lunatic,” “loon,” and “loony” all trace to the Latin luna, Moon.
- What the science actually shows: dozens of studies on ER visits, crime rates, births, and seizures find no consistent correlation with the full Moon.
- Why the belief persists: confirmation bias, plus a real historical thread of moonlight-driven sleep deprivation in pre-electric households.
- The honest exception: sleep does measurably get a little shallower around full Moon (about 20 minutes less and 30% less deep sleep in one 2013 study), though the size of the effect is small.
- What this is not: an excuse. The ER is busy because shifts are long, not because the Moon is up.
Do full moons make people act crazy? The answer is more nuanced than the myth lets on. Below is what the research shows about sleep, mood, ER visits, and animal behavior around the full Moon, plus the origin of the word “lunacy.”
“Must be a full Moon,” is a common utterance whenever things start to go a little haywire. The idea that a full Moon can drive people mad is an old one. Even the word “lunatic,” and its relatives “loon” and “loony,” derive from the Latin word luna, meaning “Moon.” Full moon behavior is one of the most enduring pieces of folk weather and sky lore in the English-speaking world.
Urban legends abound on the subject of things going haywire around the time of the full Moon. According to contemporary lore, emergency rooms and veterinary offices are busier when the Moon is full; suicide, arson, and violent crime rates increase; patients in psychiatric hospitals act out more; and there are more traffic accidents.
Others even attribute medical occurrences, such as women going into labor, epileptic seizures, and sleepwalking, to the full Moon. But is it true? The short answer is mostly no, with one small honest exception around sleep. The longer answer takes us through gravity, water, confirmation bias, and a few studies that did manage to find a faint signal.
Do Full Moons Really Affect Our Behavior?
People who believe that Moon phases affect human behavior point out that the human body is about 60% water. If the phase of the Moon can affect ocean tides, and even cause a small bulge in the Earth’s crust, surely it would exert some effect on human beings, they reason. The mechanics here are appealing but the physics do not cooperate, the gravitational pull of the Moon on a person is real but vanishingly small compared with everyday forces. (More on that in a moment.) For the tidal piece specifically, see our explainer on how the Moon affects the tide.
And, of course, one of the most popular features in the Farmers’ Almanac is our Best Days calendar, which recommends specific days to do everything from planting root crops to cutting hair for increased growth, based on the phases of the Moon and other factors. Readers swear they see better results in their endeavors when they follow these recommendations. The almanac’s position has always been: the Moon is woven into a folk calendar that has worked for generations of growers, and we publish it. The question on this page is a separate one, whether the full Moon, specifically, changes how people act.
What Does Science Say?
Science has taken the question of the full Moon’s effects seriously enough that there have been a number of studies examining the various claims, on ER visits, on births, on crime rates, on suicide rates, on psychiatric inpatient incidents, on seizures, on dog bites. Nearly all of them have come up empty. They have either found no correlation between the Moon and human behavior or were later debunked by other studies that questioned their methods (small samples, single-hospital data, no correction for day-of-week, no control for weather).
Scientists are also quick to point out that objects on Earth have more effect on one another than the Moon does. Astronomer George Abell famously noted that a mosquito sitting on your arm exerts more gravitational force on your body than the Moon does. The water-in-the-body argument fails for the same reason: a person is not an ocean, you are not large enough or fluid enough for the Moon to raise a “tide” inside you.
So why the persistent belief, purportedly even among emergency room personnel and police, in the power of the full Moon to bring on crazy behavior? One hypothesis, posed in a 1999 issue of the Journal of Affective Disorders, suggested that sleep deprivation, caused by the brightness of the full Moon, might have worsened existing mental disorders in earlier centuries. Once electric lights were invented, the authors said, the effect was negated, which is why modern studies have found no correlation in lit-up cities. A 2013 study in Current Biology (Cajochen et al.) tracked sleep in a controlled lab and found participants slept about 20 minutes less on full-moon nights and showed about 30% less deep (slow-wave) sleep, an honest-to-goodness small effect that survives even in a windowless lab. The size is small. The signal is real. For more on the sleep angle generally, see the MedlinePlus overview of sleep disorders.
Others say the belief has remained strong due to “confirmation bias,” the idea that people favor information that supports their preconceived notions. In other words, if you expect people to act strangely during a full Moon, every strange behavior you encounter during a full Moon reinforces that belief. The strange behavior on the night of a half Moon, by contrast, gets forgotten.
Full Moon Behavior Claims, Sorted
| Claim | What the studies say | Verdict |
|---|---|---|
| ER visits spike on full-moon nights | Multiple large studies; no consistent correlation | Folklore |
| Crime and arson go up | Studies in the U.S., U.K., Australia find no link | Folklore |
| More babies are born | Hospital birth data, controlled for staffing, finds no link | Folklore |
| Psychiatric inpatients act out more | Older single-site studies positive, larger reviews negative | Mostly folklore |
| Epileptic seizures cluster | Mixed findings; no strong effect | Inconclusive |
| People sleep worse | 2013 controlled study found ~20 min less sleep and ~30% less deep sleep on full-moon nights | Small but real |
| Dogs bite more | One UK ER study positive, U.S. follow-up negative | Inconclusive |
| Werewolves come out | No peer-reviewed evidence | Folklore (for entertainment value only) |
Read 7 Ways The Moon May Affect Your Health
Full Moon Behavior FAQ
Does the full Moon really affect human behavior?
For most claims (ER visits, crime, births, dog bites, psychiatric incidents), the controlled-study evidence does not support a link. The honest exception is sleep: a 2013 Current Biology lab study (Cajochen et al.) found about 20 minutes less total sleep and 30% less deep sleep on full-moon nights, even in a windowless room. The effect is small but consistent.
Why does the word “lunatic” come from “Moon”?
“Lunatic” comes from the Latin luna (Moon), via the late-Latin lunaticus, meaning “moonstruck.” The English words “loon” and “loony” trace through the same root. The vocabulary was already in place by the 13th century, centuries before any statistical study could test the claim.
Are emergency rooms really busier on full-moon nights?
Despite what many ER nurses, doctors, and paramedics will tell you, the published research does not support it. Large retrospective studies of ER admissions, ambulance calls, and trauma volume find no consistent spike around the full Moon. The perception is most likely confirmation bias plus the universal human tendency to look for a story in the data.
Does the full Moon trigger labor or more births?
No. Multiple large hospital studies (some over years and hundreds of thousands of births) have looked for a lunar effect on birth volume, induction rates, or spontaneous labor. None have found a consistent correlation.
Why does the body-is-60%-water argument fail?
Tides are caused by the gravitational pull of the Moon on enormous, contiguous bodies of water (oceans). Your body is too small and too compartmentalized to develop a tide. Astronomer George Abell’s well-known line is that a mosquito on your arm exerts more gravitational force on you than the Moon does. The physics is not strong enough at the scale of a person to do anything interesting.
Can the full Moon really mess with my sleep?
A bit. The 2013 Cajochen study and a few follow-up replications found shorter and shallower sleep on full-moon nights, even with no light reaching the sleeper. The effect is small (a fraction of an hour for most people) but it is real. Blackout curtains, a cool room, and a consistent bedtime help blunt it.
If the science is mostly no, why do I still feel “off” on full-moon nights?
Two reasons. One, you may genuinely be sleeping a little worse on those nights (real effect, see above). Two, you have a folk vocabulary for “off-ness” that the calendar invites you to use. Once you label the night a “full Moon night,” anything that does go wrong fits the story.
For more on the Moon side of the Almanac, see our supermoon guide, how to set goals with the Moon, and monthly full Moon horoscopes. Whatever you make of the lunar effect on behavior, the sky show is real.
What do you think? Do you notice people acting differently around the time of the full Moon? Share your thoughts below.
Jaime McLeod
Jaime McLeod is a longtime journalist who has written for a wide variety of newspapers, magazines, and websites, including MTV.com. She enjoys the outdoors, growing and eating organic food, and is interested in all aspects of natural wellness.
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Sho Nuff
I’m no expert on anything, more like Jack of All Trades, and through my life I’ve never seen anything that bears this notion out. People behave all sorts of ways every day of the month, including nights with full moons. I think seeing someone do something particularly egregious is fuel for this lore. That said, I am willing to change my opinion on this, especially if I see proof of someone turning into a wolf on the night of a full moon.
I worked in a hospital ER for many years. Certain times of the month one of the workers would ask to lookup the date if it was Full Moon ,cause the ER was more chaotic than normall..
I know what science says, but after working in a hospital, I can’t agree. It SEEMED as though more babies were born and more crazies were in the ER.
Totally believe it. I had to go to the ER on the super full moon this month. There were 76 patients back in the ER and I had to wait 10hrs before I went back (i had to get certain tests by a GI so i had to wait.) I was flagged as an overnight observation so that just kept checking my vitals until there was a bed. All the hospital staff were convinced it was the full moon!
You need to ask a Cancer. (-;
What’s weird is nobody ever talks about the weird behavior during a new moon, even though the tidal forces are greater than a full moon…..
I am at work right now, sitting outside, taking a break. I am looking at the full moon. I work in a dementia facility and most of my residents have been going off the chain all day. Screaming, falling down, more aggressive behavior than usual. I came outside to take a breather from all the chaos and looked up and yes, it’s a full moon.
I was a CNA as well as an EMT for quite a few years. As a CNA it only took a couple of our alzheimer/dementia patients to start acting exceptionally off-kilter before one of my coworkers would get on their phones to find out if it was a full moon. We all knew that if either of the Emma’s started to act crazier than usual, it was a full moon. In the EMS world we would get hammered with a larger call volume as well as some bizarre calls. For me personally, I get exceptionally clumsy a day or so before the moon reaches the full moon phase. IT MAKES A HUGE DIFFERENCE! Ask anyone who has porphyria, the disease of the vampire, which is where the werewolf legend came from, and they will tell you, it makes a difference.
I have been a 911 dispatcher for 20 yrs. I can tell you we notice a difference in call volume and the call types where ppl are not acting normal. We have callers we consider “regulars “ that we know they will be calling more frequently during the full moon. We believe in the full moon theory.