The short answer is probably not. Despite centuries of folklore and a strong gut feeling among police officers and emergency workers, the bulk of research finds no consistent link between a full moon and increased crime. A few individual studies have found small upticks in certain types of incidents, but the overall pattern across decades of data points to coincidence and a well-known psychological trick called confirmation bias.
What the Crime Data Actually Shows
Studies on this question go back decades, and they point in different directions depending on the dataset. One older analysis published in the British Medical Journal found that the incidence of crimes committed on full moon days was “much higher” than on other days. But a large population-based study from Finland found the opposite for homicides: during the full moon, 15% fewer homicides occurred compared to the new moon. When researchers looked more broadly at ambient light levels, homicides dropped even further during the brightest nights, falling by 86% compared to the darkest ones.
That Finnish study is particularly interesting because it flips the common assumption on its head. If anything, the data suggested that more moonlight may deter violent crime rather than encourage it, likely because potential offenders are more visible and potential victims can see threats coming. This aligns with what criminologists already know about street lighting: well-lit areas tend to have less crime.
Why the Belief Feels So Real
If you’ve ever worked a night shift in a hospital, police station, or fire department, you’ve almost certainly heard someone blame a hectic night on the full moon. The belief is remarkably persistent in these professions, and it comes down to how human memory works.
Confirmation bias is the tendency to notice and remember things that fit what you already believe while ignoring things that don’t. A police officer working a chaotic shift might glance at the sky, see a full moon, and think, “Of course.” That connection gets locked into memory. But the equally busy shifts that happen under a crescent moon or no visible moon at all don’t register the same way. As one criminal justice analysis put it, “busy nights without full moons are not noticed or counted against the theory.” Over time, a handful of vivid memories create the illusion of a pattern that isn’t there in the actual numbers.
Weekends, Holidays, and Hidden Variables
One of the trickiest parts of studying this question is separating the moon from everything else happening on a given night. A full moon falls on a Friday or Saturday roughly two out of every seven cycles, and weekends already have higher crime rates. Holidays add another layer. One study from India found what initially looked like a spike in full moon crime, but when researchers broke the data down by day of the week, the effect nearly vanished. The apparent spike traced back to a single full moon that happened to land on the Holi festival, a holiday already associated with higher incident rates.
When researchers controlled for the day of the week by comparing full moon Sundays to non-full-moon Sundays, full moon Wednesdays to non-full-moon Wednesdays, and so on, the crime rates were nearly equal across the board. The moon wasn’t the variable that mattered. The calendar was.
Psychiatric Emergencies Don’t Spike Either
A related belief holds that people act more erratically during a full moon, which should show up in psychiatric emergency rooms even if it doesn’t show up in crime stats. A large study at Naval Medical Center San Diego examined over 8,400 psychiatric admissions across eight years and nearly 1,900 emergency psychiatric evaluations across two additional years. The results were unambiguous: no increase during any phase of the moon. This held true for patients overall and for specific diagnoses like mood disorders and psychotic disorders. Lunar phase was not associated “in any significant way” with psychiatric admissions or emergency visits.
The One Exception: Animal Bites
Interestingly, one area where the full moon does seem to matter is animal behavior. A study of 1,621 patients treated for animal bites (95% of which were dog bites) found a statistically significant increase around the full moon. The rise began a few days before the full moon, peaked sharply on the day itself, then dropped to about half the peak rate shortly after. The reason isn’t mystical. Animals, especially dogs, are more active outdoors when nights are brighter, and more activity means more encounters with people. More encounters mean more bites.
This finding actually reinforces the illumination theory: a full moon changes outdoor behavior for animals and, to some extent, for people. But “more activity under brighter skies” is a far cry from the idea that the moon somehow triggers aggression or madness.
Where the Myth Comes From
The word “lunatic” literally derives from “luna,” the Latin word for moon. The idea that the moon influences human behavior is ancient, predating modern science by thousands of years. Some historical reasoning held that because the moon affects ocean tides and human bodies are mostly water, it must also pull on something inside us. The physics doesn’t support this. The gravitational force the moon exerts on a human body is vanishingly small, far less than the gravitational pull of the building you’re sitting in.
The belief persists because it’s culturally embedded, emotionally satisfying, and reinforced every time a busy night happens to coincide with a bright moon. It’s one of the most durable examples of how pattern-seeking brains can create connections that feel absolutely certain but don’t hold up when you count the numbers carefully.