From the WebMD Archives

You’ve probably heard some of these full-moon myths. A full moon makes you crazy. It messes with your sleep. It can cause seizures.

While a supermoon and a full moon are awe inspiring, can they really affect your health?

"I am certain that any effect of the supermoon on human health is not caused by any astronomical or physical effect," says Rick Fienberg, PhD, press officer for the American Astronomical Society. "There are not physical things happening that could cause any of these health effects."

Fienberg says people take notice of the moon when it is fuller and brighter and ascribe certain things that happen to it.

Folklore and legend credit terrific power to the moon. Some stories claim it controls rain, which is why farmers sometimes used the lunar phases to dictate planting and harvest and when to slaughter cattle. While it’s true the moon impacts tides, most stories about the moon are mostly that: stories not rooted in fact.

Folklore expert Merrill Kaplan, PhD, says myths regarding the moon are centuries old.

"This idea that people get weird [with full moons] goes back to the first century," says Kaplan, associate professor of folklore and Scandinavian studies at Ohio State University. The link with disease is very old, too, she says. Years ago, those with epilepsy were described as being "moon-sick."

Still, researchers have continued to study the moon phases for any health effects. Here’s what they’ve found:

Motorcycle Accidents

Canadian researchers looked at data on more than 13,000 motorcyclists involved in fatal crashes over 40 years in the U.S. and found the risk did increase during a full moon.

For every two full moon nights, there was an additional fatal crash, says Donald Redelmeier, MD, professor of medicine at the University of Toronto. The increased risk was modest, he says, but “important from a road-safety point of view.''

Redelmeier guesses the moon may distract drivers, leading to more accidents. Bikers take a moment to admire the moon, and that moment of distraction becomes tragic. "Small distractions can lead to large consequences when you are involved in roadway accidents," Redelmeier says.

Surgery Outcomes

It’s a popular trope that emergency rooms are filled on nights of a full moon. It’s common even among medical professionals, one study found.

That’s one reason why German researchers set out to discover if it was true. They evaluated the medical records of nearly 28,000 patients who were having surgery at their hospital from 2001 to 2010.

“The influence of superstition, moon calendars, and popular belief on evidence-based medicine is stunning,” the authors write. “More than 40% of medical staff is convinced that lunar phases can affect human behavior.”

The researchers matched surgery dates to lunar phases (as well as zodiac signs and Friday the 13th). None of those factors had an effect on blood loss or other surgical emergencies.

Their conclusion: "Our data indicate that such beliefs are myths far beyond reality."


Some researchers think a full moon may trigger seizures. They reviewed the neurologic records of 850 patients admitted to the ER from 1999 to 2003 for seizures. They found a significant clustering around full moons.

But researchers in a later study concluded that the nighttime brightness, not the moon phase, may influence seizures.

Mental Health Problems

Anecdotes about the moon and an increase in mood problems are common, even among mental health workers, according to researchers from Queen's University in Canada. They evaluated about 1,800 patients whose mental health was a factor in an emergency room visit. They looked at which visits took place during four phases of the lunar cycle.

Again, researchers cleared the moon of any wrongdoing. They concluded that the lunar cycle did not have an effect on the number of psychiatric problems in their study.

"If lunar effects exist, they are probably small or infrequent, making them difficult to validate statistically," the researchers write.

In another study, researchers looked at 782 patients who received care in a general practice in London. They found the moon phase had little influence on when people consulted their doctor with anxiety or depression issues.

Goodnight, moon

It's possible that the moon is keeping you awake -- a little.

In a small Swiss study with 33 people, researchers found an indicator of deep sleep measured by an EEG decreased by 30% around a full moon. Time to fall asleep increased by 5 minutes, and total sleep duration was reduced by 20 minutes.

A later study failed to reproduce the results of the Swiss study. 

But a study of 319 sleep clinic patients did find they suffered poorer sleep during the full moon.

WebMD Health News


BMJ: "The full moon and motorcycle related mortality: population based double control study."

Advances in Mind Body Medicine: "Psychiatric Presentations During All 4 Phases of the Lunar Cycle."

World Journal of Surgery: "Popular belief meets surgical reality: impact of lunar phases, Friday the 13th and zodiac signs on emergency operations and intraoperative blood loss."

Current Biology: "Evidence that the Lunar Cycle Influences Human Sleep."

International Journal of Social Psychiatry: "Lunar cycle and consultations for anxiety and depression in general practice."

Sleep Medicine: "Association between lunar phase and sleep characteristics."

Neurology: "Lunar phases and seizure occurrence: just an ancient legend?"

Epilepsy Behavior: "Moonstruck? The effect of the lunar cycle on seizures." Donald Redelmeier, MD, professor of medicine, University of Toronto.

Rick Fienberg, PhD, press officer, American Astronomical Society, Washington, D.C.

Merrill Kaplan, PhD, associate professor of folklore and Scandinavian studies, Ohio State University, Columbus.

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