Full moon causes erratic human behavior

What we know

The belief that the moon influences human behavior, sometimes called the 'lunar effect' or 'Transylvania effect' in academic literature, is ancient and cross-cultural, reflected in the etymology of the word 'lunatic' itself, derived from the Latin 'luna' for moon. The belief has persisted into modern times among some healthcare workers, police officers, and the general public, who report anecdotal impressions that emergency rooms, psychiatric wards, and crime rates become busier or more chaotic during full moons.

This claim has been tested extensively using large datasets rather than anecdotal impression, since anecdote is particularly vulnerable to confirmation bias, where staff working a busy or unusual full-moon shift remember and discuss it more than an equally busy shift during another lunar phase. A comprehensive meta-analysis published in Psychological Bulletin in 1985, reviewing 37 separate studies covering suicide rates, psychiatric hospital admissions, crisis calls, and related outcomes, found no significant relationship with lunar phase across the pooled data, and this remains one of the most frequently cited reference points in the scientific literature on the topic. Subsequent large studies have continued to test the claim using more recent and larger datasets, including a widely cited analysis of over 150,000 emergency room visits at a single US hospital system, which found no statistically significant increase in visits, psychiatric complaints, or violent injury presentations correlated with full moon dates.

Studies specifically examining crime statistics have produced similarly negative findings; a review of police-reported crime data across multiple jurisdictions, including analyses conducted by criminologists in the United States and the United Kingdom, has not established a reliable, consistent statistical link between lunar phase and crime rates once researchers control for other variables such as weekday, season, and holiday periods, all of which independently affect both crime and hospital admission rates and can create a spurious appearance of lunar correlation if not properly accounted for. Sleep researchers have examined a related, narrower claim, that full moons disrupt sleep quality, and while one frequently cited 2013 Swiss study using a small sample reported modestly reduced sleep quality around full moons, larger follow-up studies with bigger and more diverse samples, including one analysis of over 2,000 nights of data across multiple countries published in Science of the Nature journal group, failed to replicate a reliable effect, leaving the sleep-specific claim considered unresolved and, at best, a minor and inconsistent effect rather than the dramatic disruption often described anecdotally.

Cognitive scientists studying belief persistence attribute the durability of the lunar effect belief to illusory correlation, a well-documented cognitive bias in which people are more likely to notice, remember, and discuss events that confirm a pre-existing expectation, such as a chaotic night specifically occurring during a full moon, while equally chaotic nights during other lunar phases pass without the same attention or discussion, gradually reinforcing an association that pooled statistical data does not support. The physical mechanism proposed by some proponents, that the moon's gravitational pull on ocean tides might similarly pull on the water content of the human body, is also considered implausible by physicists, since the moon's gravitational effect on a body of water the size of a human being is astronomically smaller than the effect of ordinary nearby objects like furniture, and far too small to produce any physiologically meaningful effect.

Common claims

• Hospital emergency rooms and psychiatric admissions increase during full moons.False, large studies including analyses of over 150,000 ER visits found no significant correlation.
• Crime rates rise during the full moon.False, controlled analyses find no reliable link once other factors like weekday and season are accounted for.
• The moon's gravity pulls on the water in the human body, affecting behavior.False, physicists note the moon's gravitational effect on a body-sized volume of water is negligible.
• Sleep quality is measurably worse during the full moon.Unresolved, a small 2013 study suggested this, but larger follow-up studies did not reliably replicate the effect.

Evidence hierarchy

All sources

• Much Ado About the Full Moon, A Meta-analysis of Lunar-Lunacy ResearchPsychological Bulletin · 1985
• Lunar cycle effects on sleep, replication studiesScientific Reports (Nature) · 2021
• Does the full moon affect human behavior?Scientific American · 2018
• Emergency department utilization and lunar phaseNational Institutes of Health, PubMed Central · 1996

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