Why the ER is busier during a full moon
Key Takeaways
Medical lore has long suggested the ER is busier during a full moon, and it may be a phenomenon you've observed yourself.
Some studies support this, with evidence suggesting suicide rates and car crashes involving animals increase, in particular, during a full moon. However, experts say none of the studies prove causation, and observer bias may be a factor in believing the ER is busier during the full moon.
It’s a well-known lore among the healthcare community that the full moon can do crazy things to your hospital’s emergency department. On a particularly busy night or a night with unusual cases, it’s not uncommon to hear someone utter the phrase, “Is it a full moon?”
“Whenever we’re super busy or there seem to be a lot of mental health cases presenting, someone in the emergency department will always ask if it’s a full moon,” says Michael Curry, MD, a clinical associate professor in the emergency medicine department at the University of British Columbia. “But it very well could be observer bias.”
“I think it might make a small difference. Historically, it comes from the pre-electricity era, when people could more easily stay out late at night when they had the illumination of a full moon,” Dr. Curry tells MDLinx. “But in the modern era, I think it’s mainly superstition."
Superstition or not, there is evidence suggesting the full moon really does make the ER busier. Let's take a closer look at the phenomenon.
What the research says
One study found that as many as 81% of mental health workers claim anecdotal evidence that there is a relationship between human health and a full moon.[] Additionally, a 2023 study concluded that rates of suicide are higher during nights with a full moon. The study authors suggest that light from a full moon may play a role in circadian rhythms, which in turn may impact a person’s mood or suicidality.[]
But the study doesn’t prove causation. “It is hard to validate any causation between the full moon and suicide rates due to the difficulty in showing a true cause and effect relationship,” Shashank Ravi, MD, clinical associate professor of emergency medicine at Stanford, tells MDLinx. “The data shared here indicates a possible correlation, meaning there is a statistical relationship, but it is not clear what causes what, as well as what other mitigating factors may also be present.”
Another study, published in May 2024, found that full-moon nights had almost 46% more wildlife-vehicle collisions than new-moon nights.[] Older research also suggests medically unexplained strokes increase during the full moon, as do psychiatric emergency room visits.[][] Severity of illness and aggressive behaviors were also found to be significantly increased during the start and end of moon cycles.
Dr. Curry says it’s possible the impact of light on sleep may be a factor. “We have thousands of years of evolution that have acclimatized us to our natural environment, and only about 130 years of electric light, so it’s easy to think we may have some genetic predisposition to acting differently during bright nights,” he says. “Also, we know sleep has a strong relationship with mental health and that light interferes with sleep, so it’s possible to think of mechanisms connecting the light of a full moon and human behavior.”
Superstitions in medicine
Both experts who spoke with MDLinx say that regardless of whether or not the full moon actually does make the ER busier, physicians may have superstitions.
“Physicians can definitely be a superstitious group. In the emergency department for example, we are very careful not to use the ‘q’ word: quiet," Dr. Ravi says.
"Any time anyone comments on a ‘quiet’ night, the night suddenly becomes extremely busy. [I] would love to see a study conducted on this phenomenon."
— Shashank Ravi, MD
“It is definitely worth keeping an open mind about any event occurring outside the hospital walls, whether a holiday, the weather, or the moon. While there might not be direct causations, there might be many other mitigating factors around these events that lead to certain hospital presentations.”
What this means for you
It is a popular medical lore among physicians that the full moon can make the ER busier. Some studies suggest suicide rates can be higher on the full moon, as can vehicle accidents involving collisions with animals. But the studies do not prove causation. Experts note that physicians can be a superstitious bunch. Nonetheless, they also say it’s possible that light from the full moon could play a role in human behavior.