Patient Care

It’s a Full Moon Tonight

It’s an almost universal belief among emergency medical personnel that patient volumes and patient behavior are affected by the phases of the moon. Particularly, many believe that EMS calls, ED visits, childbirth, psychiatric behavior and numerous other things increase during the full moon phase of the lunar cycle. But, is this belief true? Most will recount their personal experience with things that occurred in their life during full moons. However, as with many things, belief does not always translate into reality.

For many years, the term “lunacy” was used to describe insanity and mental illness. Someone who had “lunacy” was described as being a “lunatic.” The term lunatic was actually derived from the Latin word lunaticus, which literally means “of the moon.”

Prior to the modern era, many illnesses were thought to be caused by the moon including mental illness and epilepsy. For many years, the terms “lunatic” and “lunacy” were used in the legal setting to describe people with mental illness. Fortunately, with a better understanding of most disease processes, these terms are now considered archaic.

In order to determine whether or not psychiatric emergencies or ED visits or EMS runs are related to the full moon phase of the lunar cycle, one must evaluate the actual data in an objective and scientific way. This is the only way to minimize anecdotal experience and bias. Interestingly, this has been done for several conditions, although the scientific literature specifically for EMS is limited.

To study this, it is first necessary to define a full moon or full moon phase. Most studies define a full moon as a three-day period beginning the day before the full moon and ending the day after the full moon. Some will use a five-day period beginning two days before the full moon and ending two days after the full moon.

The lunar cycle consists of multiple phases of the moon based upon how much of the lighted part of the moon is visible. This is often reported as the lunar month that is defined as the time between two successive full moons. There are approximately 29.5 days in a lunar month although these vary somewhat during the year. There are approximately 13 lunar months in a Gregorian year and the number of full moons in a calendar year will vary.

It is believed by some of the gravitational pull of the moon, which causes the tides, can have an effect on the human body causing behavioral and physiologic changes. However, in humans, this has not been identified. Some conditions have been investigated in terms of the effect of the lunar cycle on them. Here are a few examples:

1. Are heart attacks and cardiac arrests more common during a full moon?
In a New Jersey study, researchers did a retrospective analysis of northern New Jersey EDs from January 1, 1988, to December 31, 1998. They then looked at the incidence of cardiac arrest during the previously defined full moon phase. They evaluated 2,370,233 ED visits during the study. There were 6,827 patients with a diagnosis of cardiopulmonary resuscitation. The occurrence of cardiopulmonary resuscitation was not more common during the full moon interval.1

An Austrian study retrospectively looked at 368 cardiac arrest and 872 episodes of acute myocardial infarction over a six-year period (1992–1998). They concluded that lunar phases do not appear to correlate with acute coronary events leading to myocardial infarction or sudden death.2

2. Do intracranial aneurysms rupture more often during full moon periods?
It has been thought by some that the development of acute neurologic and vascular orders may be related to the phase of the moon. In one study, researchers looked at patients admitted to the hospital for ruptured intracranial aneurysms between 2011 and 2014. Overall, 186 patients were found with these conditions. They determined that the phases of the moon were not associated with the incidence of intracranial aneurysm rupture.3 Other studies reached the same conclusion.4 One found ruptures were actually more common when the moon was least luminated (i.e., new moon).5

3. Are kidney stones more common during a full moon?
Some have thought that the gravitational effect of the full moon can cause the movement of kidney stones, and thus there is an increased incidence of kidney stone during full moon phases. In a Swiss study, researchers evaluated all patients greater than 18 years of age who went to the ED in Bern over a 11- year interval with renal colic. There was a total of 1,500 consecutive patients who presented with kidney stones during the study interval. They were unable to associate an increased incidence of kidney stones with the full moon phase.6 A similar study at the University of Nebraska come to the same conclusion.7

4. Are psychiatric emergencies more common during a full moon?
It is assumed by many that a full moon causes worsening psychosis for patients with mental illness. However, the available scientific evidence reveals this to be a false belief. A 2017 study of 1,857 who presented to their ED with a psychiatric component found no difference in the number of visits during a full moon phase.8 A Mayo Clinic study found no association between psychosis and a full moon.9 The same holds true for pediatric psychiatric patients.10 A German study found no association between suicide and a full moon.11

5. Is childbirth more common during a full moon?
A longstanding belief is that the number of childbirths increase during a full moon phase. However, this is not the case. An Irish study of 10,027 deliveries over an 18-month period found no increase in deliveries during the full moon phase.12 Multiple other studies have failed to find an association between childbirth and a full moon.13–15

6. Are emergencies more common during a full moon?
For the most part, there is no evidence that ED visits, EMS runs or similar emergencies occur more frequently during a full moon phase. An Illinois study evaluated ED visits over a four-year interval (1989–1993). They concluded that there was no relationship between ED volume, ambulance runs, admissions, or admissions to monitored care during the full moon phase.16

A German study looked at the incidence of trauma during various lunar phases as well Friday the 13th and during the twelve Zodiac signs and found no association.17 There was no increase in dog bites during a full moon.18 Interestingly, there appears to be an increased incident of motorcycle collisions during the full moon phase. However, this was thought to be from driver distraction because of the full moon.19 Otherwise, a full moon has no impact on the occurrence of emergencies.20

So, how did these beliefs develop and why do they persist? First, they have been passed down from times when many medical problems were generally believed to be related to the lunar cycle. Also, it has been documented that animal behavior can be affected by the moon. For example, births in cattle are more frequent during a full moon phase but this is an evolutionary tool to minimize loss of calves by predators.

The best explanation, simply, is human nature. Most people will remember and note a full moon because the appearance is so striking. They will then recall EMS runs and certain things that are associated with a full moon. Most people do not even notice the other lunar phases (e.g., new moon, crescent moon, gibbous moon) and do not tend to associate EMS calls with these lunar phases.

Storytelling is common in EMS and medicine and there are no better stories than full moon stories. But, although great to recount for the rookie EMT, they are nothing but another EMS myth.


1. Alves DW, Allegra JR, Cochrane DG, et al. Effect of lunar cycle on temporal variation in cardiopulmonary arrest in seven emergency departments during 11 years. Eur J Emerg Med. 2003;10(3):225–228.

2. Eisenburger P, Schreiber W, Vergeiner G, et al. Lunar phases are not related to the occurrence of acute myocardial infarction and sudden cardiac death. Resuscitation. 2003;56(2):187–189.

3. Bunevicius A, Gendvilaite A, Deltuva VP, et al. The association between lunar phase and intracranial aneurysm rupture: Myth or reality? Own data and systematic review. BMC Neurol. 2017;17(1):99.

4. Wamp MA, Dibue M, Slotty P Jr, et al. Impact of the moon on cerebral aneurysm rupture. Acta Neurochir (Wien). 2013;155(8):1525–1530.

5. Banfield JC, Abdoleel M, Shankar JS. Secular pattern of aneurismal rupture with the lunar cycle and season. Interv Neuroradiol. 2017;23(1):60–63.

6. Arampatzis S, Thalmann GN, Zimmermann H, et al. Lunar tractive forces and renal stone incidence. Emerg Med Int. 2011;2011:813460.

7. Yang AW, Johnson JD, Fronczak CM, et al. Lunar phases and emergency department visits for renal colic due to ureteral calculus. PLoS One. 2016;11:e0157589.

8. Francis OJ, Kopke BJ, Affatato AJ, et al. Psychiatric presentations during all 4 phases of the lunar cycle. Adv Mind Body Med. 2017;31(3):4–7.

9. Kung S, Mrazek DA. Psychiatric emergency department visits on full-moon nights. Psychiatr Serv. 2005;56(2):221–222.


11. Biermann T, Estel D, Sperling W, et al. Influence of lunar phases on suicide: the end of a myth? A population-based study. Chronobiol Int. 2005;22(6):1137–1143.

12. Ong S, Wingfield M, McQuillan K. Labour ward activity and the lunar cycle. J Obstet Gynaecol. 1998;18(6):538–539.

13. Ochiai AM, Gonçalves FL, Ambrizzi T, et al. Atmospheric conditions, lunar phases, and childbirth: A multivariate analysis. Int J Biometeorol. 2012;56(4):661–667.

14. Margot JL. No evidence of purported lunar effect on hospital admission rates or birth rates. Nurs Res. 2015;64(3):168–173; discussion 173–175.

15. Arliss JM, Kaplan EN, Galvin SL. The effect of the lunar cycle on frequency of births and birth complications. Am J Obstet Gynecol. 2005;192(5):1462–1464.

16. Thompson DA, Adams SL. The full moon and ED patient volumes: Unearthing a myth. Am J Emerg Med. 1996;14(2):161–164.

17. Schuld J, Slotta JE, Schuld S, et al. Popular belief meets surgical reality: Impact of lunar phases, Friday the 13th and zodiac signs on emergency operations and intraoperative blood loss. World J Surg. 2011;35(9):1945–1949.

18. Chapman S, Morrell S. Barking mad? Another lunatic hypothesis bites the dust. BMJ. 2000;321(7726):1561–1563.

19. Redelmeier DA, Shafir E. The full moon and motorcycle related mortality: Population based double control study. BMJ. 2017;359:j5367.

20. Coates W, Jehle D, Cottington E. Trauma and the full moon: A waning theory. Ann Emerg Med. 1989;18(7):763–765.