Moon Phases Affect Behavior
The belief that the full moon increases violent crime, psychiatric crises, or erratic behavior is not supported by the weight of controlled evidence. Large systematic reviews and prospective studies have found no reliable association between lunar phase and rates of violence, psychiatric admissions, or crime. Some preliminary evidence suggests a subtle effect on sleep duration, but this is modest and the mechanism unclear.
What we know
Belief in a 'lunar effect' on human behavior is ancient and persistent. Studies examining this claim date back decades and span many countries and outcome measures. A landmark 1985 meta-analysis by Rotton and Kelly combined findings from 37 studies and concluded that lunar phase was unrelated to psychiatric admissions, murders, car accidents, suicides, or crime. When individual studies did find links, they could often be explained by confounds such as weekends or holidays coinciding with full moon periods. The predictive power of knowing the moon's phase was negligible, improving behavioral prediction by approximately 1%.
Subsequent large prospective studies have consistently found no association between lunar phase and violent incidents in psychiatric settings, emergency department presentations, crime rates, or suicide. A 2017 study examining 1,857 psychiatric presentations across all four lunar phases found no statistically significant differences in rates or diagnostic categories.
The picture is somewhat more nuanced for sleep. A 2013 analysis revisiting data from a sleep study where participants were unaware of any lunar monitoring found that sleep was about 20 minutes shorter and deep (NREM) sleep 30% lower around the full moon. A 2021 study of Indigenous communities in Argentina and students in Seattle found consistent sleep reductions around the full moon across very different lighting environments. However, these findings are contested, methodologically variable, and may reflect an ancient circadian adaptation to natural light cycles rather than a direct gravitational or electromagnetic effect.
Claims that the moon affects behavior through gravity (tides in the body) are physically implausible: the Moon's tidal force on the human body is far weaker than the gravitational effect of nearby objects like a car, and the brain is not a tidal basin. The 'human body is 60% water, so the moon affects it like tides' argument is a misapplication of physics.
Common claims
- There are more violent incidents and psychiatric crises during the full moon.False. Multiple large prospective studies and meta-analyses find no reliable association. Studies that found links often failed to control for day-of-week confounds.
- Hospitals and police see more incidents during a full moon.False. This is a widely reported belief among healthcare and law enforcement workers, but controlled studies consistently fail to confirm it.
- The Moon affects our bodies like ocean tides because we are mostly water.False. Tidal forces act on large bodies of water in fixed basins. The Moon's gravitational differential across a human body is negligible, far less than that of everyday objects nearby.
Evidence hierarchy
All sources
- Lunar cycles and violent behaviourPubMed / Australian and New Zealand Journal of Psychiatry · 1998
- Psychiatric Presentations During All 4 Phases of the Lunar CyclePubMed / The Journal of Psychiatric Practice · 2017
- The lunar cycle: effects on human and animal behavior and physiologyPubMed / Psychotherapy and Psychosomatics · 2006
- Can the moon influence human health?National Geographic · 2024
- Does the full moon affect behaviour?BBC Future · 2013