Bad Moon Rising? Lunar Cycle May be Linked to More Veterinary Visits, According to Colorado State University Study

A new study suggests that dogs and cats may get into more medical mischief during certain phases of the lunar cycle. The study, authored by Dr. Raegan Wells, a veterinarian, and her colleagues at Colorado State University’s College of Veterinary Medicine and Biomedical Sciences, shows a possible link between an increase in emergency room visits for dogs and cats during days when the moon is at or near its fullest.

The data, compiled from 10 years of nearly 12,000 case histories of dogs and cats treated at the university’s Veterinary Medical Center, indicates that the risk of emergencies on fuller moon days was 23 percent greater in cats and 28 percent greater in dogs when compared with other days. The types of emergencies ranged from cardiac arrest to epileptic seizures and trauma, and the increase was most pronounced during the moon’s three fullest stages – waxing gibbous, full and waning gibbous.

Wells said this is the first time the lunar cycle’s relationship to emergency veterinary medicine has been studied. The study, titled “Canine and feline emergency room visits and the lunar cycle: 11,940 cases (1992-2002),” appears in the July 15 issue of the Journal of the American Veterinary Medical Association.

“If you talk to any person, from kennel help, nurse, front-desk person to doctor, you frequently hear the comment on a busy night, ‘Gee, is it a full moon?’ ” said Wells, who is an emergency and critical care medicine resident in the Department of Clinical Sciences at the university. “There is the belief that things are busier on full-moon nights.”

Just what is behind the correlation, however, isn’t clear.

“While the results of our retrospective study indicate that there is an increased likelihood of emergency room visits on the days surrounding a full moon, it is difficult to interpret the clinical significance of these findings,” Wells writes. “Many studies have investigated the effect of the moon on human nature, behavior and various medical problems, with evidence both supporting and refuting the effect.”

Wells cautions that, while the percentage of increase in emergencies during fuller moon days may be large, the correlation to an actual number of animals is actually quite low. The university’s Veterinary Medical Center’s critical care unit may see a few cats and a few dogs on a night without a full moon, and data showed an increase by about one cat or one dog during fuller moon days.

In addition, data did not indicate that there was an increase in aggressive behavior in pets during a full moon. For example, there was not a measurable increase in injuries from dogs acting aggressively.

The study notes the potential explanations for an increased number of visits during a full moon, but the data does not provide conclusive results. For example, one theory was that full moons provide increased luminosity, which may correlate to an expected increase in nocturnal hunting rates among cats. If so, felines may be injured more often during these evenings. However, more feline cases related to trauma were not evident in the data.