Years ago, my girlfriend was the trauma department director, and she constantly claimed that there were more ER visits during a full moon. Now, I was much nicer to her than I would be to an anti-vaxxer, so I kind of laughed. But I wasn’t so sure.
Then I kept hearing that claim from who I thought were rational and sane physicians. They just firmly believed that ER visits skyrocketed during a full moon. I knew there would be data out there to support or debunk this claim, so today, as we approach a full moon, to find out what’s out there.
Let’s take a look at the evidence, and hopefully, settle the question for a long time. And I’m going to take bets that several ER physicians will post in the comments their anecdotes that “prove” their beliefs.
ER visits and a full moon — what say the evidence?
Believe it or not, this topic has been the subject of actual research published in real peer-reviewed medical journals. This simplifies my life because I thought I would have to dig through some obscure database, and then actually have to pull out my ancient statistical analysis “skills” to decipher the data. Lucky for me, someone has already done the hard work for me.
In a paper published in March 1996 in the American Journal of Emergency Medicine, emergency physicians David A Thompson, MD and Stephen L Adams, MD examined 150,999 patient visits to an ED (emergency department) during the four-year study period. While this emergency department experienced 49 full moons over that period, there was no statistical difference in emergency room visits between a full moon and other days. The authors concluded:
No significant differences were found in total patient visits, ambulance runs, admissions to the hospital, or admissions to a monitored unit on days of the full moon. The occurrence of a full moon has no effect on ED patient volume, ambulance runs, admissions, or admissions to a monitored unit.
In an article published in Nursing Research, Jean-Luc Margot, Ph.D., Professor, Department of Earth, Planetary, and Space Sciences and Department of Physics and Astronomy, University of California, Los Angeles, examined whether the full moon had any effect on birth rates or hospital admission rates. Basically, Margo re-analyzed data from a paper that claimed that the full moon had a positive effect on the rates of birth and hospital admissions. Dr. Margot concluded:
Their report contains a number of methodological and statistical flaws that invalidate their conclusions. Reanalysis of their data with proper procedures shows no evidence that the full moon influences the rate of hospital admissions, a result that is consistent with numerous peer-reviewed studies and meta-analyses. A review of the literature shows that birth rates are also uncorrelated to lunar phases.
In a paper published in Pediatric Emergency Care, the researchers analyzed pediatric psychiatric ED visits between 2009 and 2011. Patients aged between 4 and 21 years presenting to Miami Children’s Hospital ED with a primary psychiatric complaint were included in the study. The authors found:
Our results failed to show a statistical significance when comparing the number of pediatric psychiatric patients presenting to a children’s hospital ED during a full moon and a non-full moon date.
In an article published in May 2019 in Circulation Reports, Japanese researchers examined a total of 29,552 OHCA (out of hospital cardiac arrest) that occurred on 148 full moon nights and 58,707 OHCA that occurred on 296 control nights. What did they conclude?
In this population, there was no significant difference in OHCA occurrence between full moon and control nights.
In an article published in July 1989 in the Annals of Emergency Medicine, the authors examined a total of 1,444 trauma victims admitted to the hospital during one calendar year. Full moons were defined as three-day periods in the 29.531-day lunar cycle, with the middle day being described in the world almanac as the full moon. Once again, the authors concluded, “that the belief in the deleterious effects of the full moon on major trauma is statistically unfounded.”
I could keep going, but I think I’m going to bore the reader. The overwhelming majority of papers published on this topic showed that there was no increase in ER visits, trauma, psychiatric emergencies, or anything during a full moon.
There are no biologically plausible links between the full moon and sudden emergencies. Now it’s possible that a full moon might be responsible for automobile accidents, but the effect is small and might just become statistical noise over a year.
I think this full moon myth is largely based on anecdotes and confirmation bias. On the evenings of a full moon, maybe the physicians and nurses in the emergency room remember patient visits more than on other days, and then it feels like the full moon has something to do with it.
But this belief has real-world consequences. Many emergency departments add extra staff on full moon evenings. And that comes at added cost to the hospital.
As Kaiser Permanente’s Chair of Emergency Medicine Chiefs, Karen Murrell, MD had to say:
For over thirty years in the ED, working in a variety of settings, I have heard about the effects of the full moon hundreds of times from ED staff of all levels. Some hospitals even rearrange staffing unnecessarily and at cost. While there may be a random bad year when some hospitals have an increase in patients, it is comforting to know that this has nothing to do with the status of the moon and we can base our staffing predictions on real-time data.
- Coates W, Jehle D, Cottington E. Trauma and the full moon: a waning theory. Ann Emerg Med. 1989 Jul;18(7):763-5. doi: 10.1016/s0196-0644(89)80014-9. PMID: 2735596.
- Kamat S, Maniaci V, Linares MY, Lozano JM. Pediatric psychiatric emergency department visits during a full moon. Pediatr Emerg Care. 2014 Dec;30(12):875-8. doi: 10.1097/PEC.0000000000000291. PMID: 25407032.
- Margot JL. No evidence of purported lunar effect on hospital admission rates or birth rates. Nurs Res. 2015 May-Jun;64(3):168-73; discussion 173-5. doi: 10.1097/NNR.0000000000000086. PMID: 25756232; PMCID: PMC4418782.
- Onozuka D, Nishimura K, Hagihara A. Full moon and traffic accident-related emergency ambulance transport: A nationwide case-crossover study. Sci Total Environ. 2018 Dec 10;644:801-805. doi: 10.1016/j.scitotenv.2018.07.053. Epub 2018 Jul 11. PMID: 29990928.
- Román EM, Soriano G, Fuentes M, Gálvez ML, Fernández C. The influence of the full moon on the number of admissions related to gastrointestinal bleeding. Int J Nurs Pract. 2004 Dec;10(6):292-6. doi: 10.1111/j.1440-172x.2004.00492.x. PMID: 15544585.
- Sado J, Morikawa K, Hattori S, Kiyohara K, Matsuyama T, Izawa J, Iwami T, Kitamura Y, Sobue T, Kitamura T. Full Moon and Out-of-Hospital Cardiac Arrest in Japan - Population-Based, Double-Controlled Case Series Analysis. Circ Rep. 2019 May 8;1(5):212-218. doi: 10.1253/circrep.CR-18-0030. PMID: 33693140; PMCID: PMC7889489.
- Thompson DA, Adams SL. The full moon and ED patient volumes: unearthing a myth. Am J Emerg Med. 1996 Mar;14(2):161-4. doi: 10.1016/S0735-6757(96)90124-2. PMID: 8924138.
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