There are many common beliefs about how the full moon can influence everything from sleep quality to mental health and heart health. However, research on this is limited.

In Shakespeare’s “Othello,” the maid Emilia tells Othello that the moon has drawn too close to the Earth — and driven men insane.

The idea that a full moon can stir up emotions, provoke bizarre behavior, and even cause physical illness isn’t just a literary trope. It’s a strongly held belief, even today.

As powerful as this ancient belief appears to be, there’s little science to back up the theory that a full moon causes a swift uptick in emergency room visits or mental health unit admissions.

Here’s what researchers have found about the moon’s effects on human bodies and behavior.

For centuries, physicians and philosophers blamed behavioral changes on the pull of the moon. The word “lunatic,” after all, stemmed from the idea that changes in mental state were related to lunar cycles.

The connection between the two is even supported in historic legal treatises. For instance, famed British jurist William Blackstone wrote that people gained and lost their ability to reason according to the moon’s shifting phases.

The “lunar effect” is based on the belief that health and behavior are altered during specific stages of the lunar cycle, with some claiming that it can affect everything from reproductive health to sleep quality and beyond.

Sources of superstition

The idea that the moon impacts certain aspects of physical and mental health can be tracedTrusted Source back to ancient Greece and Rome and is well-documented in the writings of classical authors like Aristotle and Lucilius.

During the 1970s, psychiatrist Arnold Lieber theorized that the moon influenced the body’s “biological tides” and altered human behavior, leading to increased rates of violence and homicide.

While many of these theories have since been debunked, the possibility that humans could be affected by the moon’s cycles isn’t entirely groundless.

The ocean’s tides rise and fall in time with the moon’s phases, and several marine species — includingTrusted Source reef coral, sea-dwelling worms, and some fish — have reproductive cycles that are roughly timed to lunar cycles.

Still, not many studies link the moon to human behavior and health conditions. Here’s what researchers can tell us about the connections that do exist between people and the full moon.

When the moon is full and bright, it may affect the quality of your sleep.

May affect sleep latency

Interestingly, one 2021 studyTrusted Source found that people fell asleep later and slept less overall up to five nights before a full moon. Study authors also found that the effect was heightened in areas where people had reduced access to artificial light.

The human body has adapted to eons of exposure to daylight and darkness.

This has led to the development of circadian rhythms that affect many of your body’s systems — not just your sleep-wake cycle. Circadian rhythms affect your physical and mental health, too.

But the widespread use of electric light means many of your circadian rhythms are adapting to new light and dark patterns. When circadian rhythms wobble, it can cause or increaseTrusted Source symptoms of certain mental health disorders, including:

  • anxiety
  • bipolar disorder
  • depression
  • schizophrenia

Does the full moon still have the power to disrupt your circadian rhythm? It brightens the sky by a lowly 0.1 to 0.3 luxTrusted Source compared with a single streetlight (15 lux) or a cell phone screen (40 lux).

So, are full moons really associated with changes in mood and mental health?

A 2019 reviewTrusted Source of nearly 18,000 medical records from different facilities found there is no relationship between lunar cycles and the length of hospital stays or the number of inpatient admissions or discharges at psychiatric facilities.

As the moon comes closer to the Earth, its gravitational pull changes — and the Earth’s large bodies of water respond with higher tides.

Scientists have wondered whether the changing gravitational pull might also affect how fluids react inside your body. Here’s what they found.

May affect blood pressure

A 2021 studyTrusted Source measured the effects of changing lunar cycles on the cardiovascular system of 42 people with type 2 diabetes. It found that lunar cycles did not influence blood pressure but did impact other related functions, including blood sugar levels and heart rate.

However, this finding conflicts somewhat with other research — including a 2020 studyTrusted Source on male athletes that found no significant difference in athletic performance during different lunar phases.

For decades — possibly even centuries — people have persisted in believing that there are more assaults, traumas, and suicides during full moon periods.

Numerous researchers have tackled these questions. They’ve reviewed records, conducted their own studies, and came to this conclusion: A full moon doesn’t cause an increase in these human behaviors.

In fact, one study found that during a full moon, incidence of homicide dropped slightly. Similarly, another study showedTrusted Source that there was no significant difference in admissions at a trauma center during a full moon.

The moon and menstrual cycles

The moon takes roughly a month to orbit the Earth. Since many menstrual cycles are about the same length, people have made a connection between the moon and its effects on menstrual periods — but they’re not actually synchronized.

A 2021 studyTrusted Source confirms this. In the study, researchers followed 529 females through six menstrual cycles — and they found no association between lunar phases and the onset of menstrual cycles.

On the subject of human reproductive cycles, it may also comfort you to know that a full moon isn’t going toTrusted Source send you into a sudden delivery if you’re pregnant, either.

An illusory correlation is a type of thinking error. It happensTrusted Source when you draw the wrong conclusion because you haven’t taken into account all the data — just some of it.

For example, if you visit a new city and have a few unpleasant encounters with locals, you might come away thinking that everyone from that city is rude. In coming to that conclusion, you’d be overlooking many positive or neutral interactions you had and focusing only on the negative ones.

Similarly, people may have noticed a behavioral episode or a traumatic incident and chalked it up to the full moon because they’ve heard myths about an association between the two.

Because the moon’s cycles are known to influence natural phenomena like the tides, some cultures have developed a belief that lunar phases also influence human emotions, behaviors, and health.

For the most part, a full moon doesn’t cause people to become more aggressive, violent, anxious, or depressed.

There’s some evidence that a full moon can lead to less deep sleep and a delay in entering REM sleep. In addition, some studies have shown a slight change in cardiovascular conditions during a full moon.

Scientists continue to study how the moon influences various physiological and psychological systems. For now, though, it appears the effect of this heavenly body on your body is less powerful than once believed.