Ain Raal, a professor of pharmacognosy at the University of Tartu and one of the study's authors, noted that, according to common beliefs, people tend to be more nervous and aggressive during a full moon. It is also widely thought that traffic accidents increase and that psychiatric clinics see more patients during this period.

"Our pharmacists have observed for decades that conflicts with patients tend to rise during a full moon. However, pharmacies are different from many other service sectors in that people who come there often have a health issue," Raal told ERR.

This observation prompted Raal to investigate the validity of this belief through pharmacies. The research team asked employees at several dozen pharmacies to record dates and complete a chart indicating, on a set scale, the number of difficult patient interactions they experienced during their shifts.

The researchers divided the participating pharmacies into two groups. One group was informed that the study focused on full moon days, while the other group was kept in the dark about the study's specific focus. "If you compare it to drug trials, the second group served as a placebo," Raal explained.

"In reality, we didn't only study the full moon day itself, but also the three days before and after the full moon's peak. The large data set enabled us to analyze the results statistically. Thanks to this approach, we can state with certainty that both groups experienced a significant increase in the number of challenging patients on full moon days," the researcher pointed out.

But how can these findings be explained? Raal is convinced that the celestial body itself doesn't directly influence people. Instead, he believes the phenomenon can be attributed to an unconscious form of self-suggestion.

"Many people with psychological issues are well aware of beliefs surrounding the full moon. They may look at a calendar or up at the sky and, without consciously realizing it, subconsciously suggest to themselves that they're going to feel worse and can justify treating others poorly," Professor Raal explained.

Belief not that old

The research team began their work by investigating folklore to understand ancestral Estonian beliefs about the full moon and lunar phases, particularly regarding health. Somewhat surprisingly, they found that these beliefs are not very old.

"In general, there aren't many lunar-phase beliefs tied to health in our culture, especially over the last couple of centuries. However, for some reason, a kind of 'new folklore' has emerged over the past 50 years, spreading widely," noted Raal. For example, while werewolves are part of Estonian mythology, relevant myths have been associated with the full moon only recently.

Explaining why people began to believe that a full moon might cause nervousness or irritability is challenging, Raal said. However, one possible reason may be the impact of moonlight on sleep.

"Recently, I was at my country home during a full moon. It was so bright outside that I didn't need a flashlight. Now, imagine how people slept in earlier times. There was likely much more light during a full moon, which would have affected their sleep cycles. People may simply have become more irritable when they couldn't get proper rest," Raal suggested.

In older folk beliefs, Raal pointed out, the focus was not solely on the full moon but on lunar phases more broadly. "A lot is said about the waxing and waning moon – specifically, the new moon and the old moon. Among indigenous peoples, there is an understanding that what happens in nature also affects humans," he said.

"When the moon was waxing, people believed that activities progressed more smoothly. For instance, if someone was building a house, they'd start during the new or waxing moon. Medicinal plants were also gathered during a waxing moon, as they were believed to hold more healing power. Meanwhile, illnesses were treated during a waning moon to diminish or eliminate them," the professor added.

The same principles are applied in agriculture. "If you wanted to grow something above ground, you did it during a waxing moon; for crops grown underground, you planted during a waning moon. There were quite a few such beliefs," Raal concluded.

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