Moonstruck! Does The Full Moon Influence Behavior?


It happens at least once every month. Sometimes, rarely, it happens twice a month. Up there in the sky. It's a bird. It's a plane. No, it's a FULL MOON.

Popular legend has it that the full moon brings out the worst in people: more violence, more suicides, more accidents, more aggression. The influence of the moon and behavior has been called "The Lunar Effect" or "The Transylvania Effect." The belief that the full moon causes mental disorders and strange behavior was widespread throughout Europe in the middle ages. Even the word "lunacy" meaning "insanity" comes from the Latin word for "moon."

You may hear people say,

"Just ask an emergency room nurse or a police phone operator. They will tell you that they are busier on nights when there is a full moon."

Is there scientific evidence to support these beliefs? Let's look at the data.

Violence, Aggression and Crime

  • 11,613 cases of aggravated assault in a 5-year period: assaults occurred more often around the full moon.
    Reference: Human aggression and the lunar synodic cycle (1978)

  • 34,318 crimes in a 1-year period: crimes occurred more frequently during the full moon.
    Reference: J. Psychology, vol. 93:81-83, 1976.

  • 58,527 police arrests in a 7-year period: no difference in the number of arrests made during any phase of the moon.
    Reference: Antisocial behavior and lunar activity: a failure to validate the lunacy myth (1977)

  • 361,580 calls for police assistance in a 3-year period: calls had no relationship to the phase of the moon when the day of the week, holiday and year were controlled.
    Reference: Perceptual and Motor Skills, 57:993-994, 1983.

  • 908,000 service calls to police in a 8-year period: calls to police did not increase during the full moon.
    Reference International Journal of Criminal Justice Sciences, 12:129-138, 2017.

  • 1,289 aggressive "incidents" by hospitalized psychiatric patients in a 105-week period: no significant relationship between the severity or amount of violence/aggression and phase of the moon.
    Reference: Lunar cycles and violent behaviour (1998)

  • The rate of agitation in 24 nursing home residents in a 3-month period: no significant relationship of agitation to moon phase.
    Reference: Full moon: Does it influence agitated nursing home residents? (1989)

  • The number of aggressive offenses (fighting, threatening or assaulting an officer, creating a disturbance) for 1,300 male inmates in a medium security prison in a 1-year period: no significant relationship between agressive offenses and moon phase.
    Reference: Full moon: Aggression in a prison setting as a function of lunar phases. (1998)

  • 1,329 assaults in four prisons in a 2-year period: no difference in the number of assaults on full moon and non-full moon days.
    Reference: Atlas, R., Violence in prison. Environmental influences, Enviro. Beh., 16:275-306, 1984.

  • 2,017 homicides in a 3-year period: no relationship between the number of homicides and the phase of the moon.
    Reference: Porkorny, A.D., Moon phases, suicide, and homicide, Am. J. Psychiatry, 121:66-67, 1964

  • 20,500 homicides in the United States in a 1-year period: no relationship between the number of homicides and the phase of the moon.
    Reference: Temporal variation in suicide and homicide (1979)

  • 6,808 homicides committed in Finland over a 54-year period: there were 15% less homicides committed during the full than committed during the new moon.
    Reference: Nayha, S., Lunar cycle in homicides: a population-based time series study in Finland, BMJ Open, 2019;9:e022759. doi: 10.1136/bmjopen-2018-022759 (2019)

  • 1,840 incidences of "acting-out" in people in a psychiatric treatment facility in a 3-year period: no relationship between the number of acting-out incidences and the phase of the moon.
    Reference: Lunar phase and acting-out behavior (1986)

  • 23,142 incidences of battery (aggravated assault) in a 7-year period in Germany: no relationship between the number of aggravated assaults and the phase of the moon.
    Reference: Relationship between lunar phases and serious crimes of battery: a population-based study (2010)

  • 12,200 incidences of aggression in people with intellictual disabilities in a 17-year period: no relationship between aggressive incidents requiring intense physical restraint and the full moon.
    Reference: The aggressive behavior of individuals with intellectual disabilities is not affected by a full moon: a 17-year study (2015)

  • 908,000 service calls to the police in a 8-year period: no relationship between calls for service and full moon.
    Reference: When the full moon rises over the Sunshine State: A quantitative evaluation of Queensland police calls (2017)

Anxiety, Depression and Psychosis


Emergency Room Calls/Emergency Room Visits/Hospital Admissions

Drug Use/Overdose

  • 1,182 drug overdose cases recorded in a 15-month period: no relationship between overdose cases and the full moon phase.
    Reference: Drug overdose and the full moon (1980)

  • 949 cases of drug use (toxicology screenings) in a 1-year period: no relationship between drug use and the phase of the moon.
    Reference: Hospital-based toxicology: patterns of use and abuse (1990)

  • 17,066 psychiatric inpatient treatment cases in an 11-year period: no relationship with admissions, discharge rates or length of stay of psychiatric inpatients with lunar phase.
    Reference: Is it the moon? Effects of the lunar cycle on psychiatric admissions, discharges and length of stay, Swiss Med Wkly, 149:w20070 (2019)

  • 2,403 patients (drug abuse) and 10,501 patients (psychiatric illness, not drug abuse) admitted to an emergency department in a 7-year period: no relationship between admissions and the phase of the moon.
    Reference: Declining rate of substance abuse throughout the month (2001)


Animal Bites


Problems Studying the Lunar Effect

Perhaps one of the first things that you notice about these studies is that the results are inconsistent. Some studies show that a particular behavior will occur more often during the full moon and other studies show no relationship between behavior and the full moon. This finding alone casts doubt on the theory that the full moon influences behavior. It may also be that experiments have been designed differently. For example, some studies include "full moon" behaviors that occur a few days before and after the full moon, while other studies include only those behaviors within a single day of the full moon.

Selective Memory?

Because many people believe that the full moon can influence behavior, experiments must be designed carefully to eliminate the possibility that people's beliefs will influence the data. For example, if people know that they are in an experiment which studies how the moon affects behavior, they may act in ways that change the results. It is possible that people have a "selective memory" for strange events that happen on the full moon; they remember strange incidents that occur during a full moon, but forget when these same things happen at other times.

Correlation Does NOT Mean Causation

It is also important to remember that studies that examine relationships between behavior and the phase of the moon determine only correlations. These types of studies determine if one set of numbers varies in a reliable manner with another set of numbers. If they do, then it can be said that a relationship exists.

The existence of a relationship between two "variables" DOES NOT mean that one variable causes the other variable. For example, if you looked for a relationship between the number of points scored by a basketball team and the number of books checked out of a library on different days, you might find a significant relationship. This doesn't mean that the score of basketball games causes people to check out library books or that checking out library books causes the basketball team to score more points. The reason why these two activities vary in a similar fashion is completely unknown and untested. It just happens that the two measurements vary in a related fashion.

In the basketball/library book example, the relationship could be caused by many things, maybe even by the weather. Maybe there was a lot of rain when the basketball scores and library books were counted. Perhaps the rain caused the basketball players to practice more (resulting in more points scored) and caused more people to visit the library (resulting in more checked-out books).

Some experiments do show that on days with a full moon there is more abnormal behavior. However, many of these studies have been criticized because they were not performed properly. For example, some of these experiments:

  • tested only a few people over a short period of time.
  • did not analyze the data with proper statistical tests.
  • did not take into account the day of the week on which the full moon occurred
  • did not take into account whether the full moon occurred on a holiday or a weekend.

Although most experiments fail to show a relationship between the phase of the moon and abnormal behavior, the belief in the "lunar effect" is still strong among many people. Unfortunately, the occasional newspaper story that describes strange behaviors during a full moon only reinforces this myth.

Did you know?

The full moon appears once every 29.53 days.

The distance between the moon and the Earth varies from about 221,438 miles (356,410 kilometers) to 252,681 miles (406,697 kilometers). The average distance between the moon and the Earth is 238,828 miles (384,400 kilometers).

The diameter of the moon is 2,160 miles (3,476 kilometers). For comparison, the diameter of the Earth is 7,926 miles (12,756 kilometers).

The circumference of the moon is 6,790 miles (10,927 kilometers). For comparison, the circumference of the Earth at the equator is 24,902 miles (40,075 kilometers).

Sometimes there are two full moons in one month. It IS possible to have a month without a full moon, but this does not happen very often and it can happen only in the month of February. You will have to wait until February 2018 for the next month without a full moon.

The surface gravity of the moon is 1/6 that of the Earth.

The first lunar landing occurred on July 20 at 4:18 p.m. (EDT) when the Apollo 11 Lunar Module touched down on the moon at Tranquility Base (Sea of Tranquility). At 10:56 p.m., astronaut Neil Armstrong touch one foot to the moon's surface. (Source: NASA)

More information about the full moon and behavior:

  1. Do things get crazy when the moon is full? - from the Straight Dope
  2. The full moon and lunar effects - from the Skepdic's dictionary
  3. Chudler, E.H., The power of the full moon. Running on empty?, in Tall Tales about the Mind and Brain. Separating Fact from Fiction, edited by S. Della Sala, Oxford: Oxford University Press, 2007, pp. 401-410.
  4. Supermoons and Behavior
moon phases

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