The Full Moon and Your Mood: Separating Myth from Science

A restless night, a difficult wake-up, and unusual irritability… Could the full moon be to blame? This belief is ancient and widely held. However, scientific research paints a much more nuanced picture: the full moon has not been proven to be a direct cause of mood swings, psychological crises, or unusual behavior. On the other hand, several studies have observed variations in sleep patterns around certain lunar phases.

This is likely where the real issue lies. When a night’s sleep is less restorative, its effects can linger throughout the day, leading to fatigue, reduced vigilance, irritability, and a diminished capacity to regulate emotions.

Sleep: The Primary Observed Link

A study published in Current Biology in 2013 found that, under controlled laboratory conditions, brain activity associated with deep sleep decreased by 30% around the full moon. Participants also took approximately five minutes longer to fall asleep and slept an average of 20 minutes less. Researchers also observed a decrease in melatonin, a hormone involved in sleep regulation.

However, this conclusion has not become a scientific consensus. A much larger study involving 2,125 people found no statistically significant difference in sleep duration or quality between the different phases of the moon.

In other words, the results are not homogeneous enough to claim that the full moon systematically causes everyone to sleep worse.

Nevertheless, other studies provide interesting insights. A study published in Science Advances in 2021, based on data collected in various environments, found that participants tended to fall asleep later and sleep for shorter periods in the days leading up to the full moon, when moonlight is available at the beginning of the night. The analysis included, among others, 463 American students and several populations living in Argentina.

What About the Feeling of Having “Less Energy”?

This is where it is crucial to distinguish between perception and demonstrated biological mechanisms.

There is no robust evidence to support the claim that the full moon “drains energy” or directly increases fatigue. However, a shorter or more fragmented night of sleep can indeed alter emotional state and cognitive abilities the following day. A large meta-analysis published in Psychological Bulletin in 2024 synthesized 154 experimental studies and 1,338 effect estimates, representing 5,717 participants. It concluded that various forms of sleep deprivation reduce positive emotions and increase certain symptoms of anxiety.