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Full moon

Does the moon really affect us?

People have long been fascinated with how the moon affects us. Does it affect our moods, our sleep, a woman’s menstrual cycle? Many believe so, because of the moon's gravitational effect on the earth's oceans. We look at what the science says, and separate fact from fiction.

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The pull of the moon - evidence and stories

The earth experiences around 12-13 full moons and 3 lunar eclipses a year, and a blue moon every 2-3 years. The idea that the moon affects our minds and bodies can be found in history, folklore, and classical and modern storytelling. To get to the truth, we need to look at the evidence, but much of this is anecdotal, with very little scientific research to back up people's stories.

As many as 81% of mental health workers believe there's a relationship between a full moon and psychiatric illnesses1. Yet, a large study that attempted to turn this anecdotal evidence into scientific data failed to find that a full moon had any notable effect on psychiatric symptoms in one hospital's emergency ward1. It concluded that if lunar effects exist, they are likely to be too small or infrequent to validate in studies.

The moon, our bodies, and water

A full moon is associated with spring tides, where the changes in sea levels between low and high tide are at their most extreme. The same is true for blue moons and supermoons, which are types of full moons.

This is the basis of some of the theories around why the moon affects humans - because of the amount of water in our bodies. The brain and heart are composed of around 73% water, the lungs 83%, skin 64%, muscles and kidneys 79%, and bones 31%2. Those who believe that the moon affects us believe that the water inside us is influenced by the moon's position, just as the tides are. However, this has never been proven scientifically.

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The moon and our moods

As far back as Ancient Greece, people have turned to the moon to explain away incidences of extreme behaviour and misunderstood mental illnesses. This has spawned terms like 'howling at the moon'.

Jo Clayton is a psychotherapist and counsellor. She says "The link between mental health and unpredictable or extreme behaviour has been grounded in our language for millennia, yet we don't seem to be any further towards understanding it. Many of us psychotherapists are more than a little sceptical there is any proven link at all, despite the extensive and ongoing research on the subject. This could be a phenomena, but it might also just be a fantasy.”

However, not all mental health professionals are in agreement. One study of 18 patients with rapid-cycling bipolar disorder concluded that patients manic-depressive episodes synchronised when the moon's affect on the tides were strongest3. The author, a professor of psychiatry, concluded that a lunar influence was likely, given that this couldn't be explained by biological processes within the patients.

The moon and sleep

There is some evidence to support that moon phases can interfere with our circadian rhythm, the 24-hour cycles making up part of the body's internal clock.

"The full moon phase seems to be the most problematic, with research suggesting it can take longer to fall asleep, and to reach REM sleep. Deep sleep seems to be reduced by as much as 30%, with increased interruptions and awakenings," says Clayton, who also points out some people may also sleep for shorter periods of time.

A 2021 study found that sleep generally started later and is shorter on the nights before the full moon when moonlight is available during the hours following dusk4. The study data also suggested that strong moonlight likely stimulated nighttime activity and prevented sleep in preindustrial communities - remote communities who have no access to artificial light and therefore rely entirely on sunlight and moonlight to guide their sleep.

It's worth noting that this evidence is for the effects of moonlight as a stimulant - and there remains no scientific evidence for the moon's gravitational pull on our bodies.

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The moon and menstruation

There appears to be no evidence that the phases of the moon can influence birth rates, contrary to popular folklore. However, recent studies have found some evidence linking the moon phases, which are 29.5 days long, and women's menstrual cycles, which vary but are around the same length.

In one long-term study, researchers found that some women's periods syncronise with moonlight and gravity cycles at certain points in their lives5.

According to Clayton, the most compelling data, coming from menstrual tracking apps, is that "sleep seems to be more restful during a woman's period when the moon is more than half full."

For example, research using the Luna Luna app found that most women slept better if their period began during the light lunar period around a full moon, while most who started their period during the dark time around a new moon had poor sleep7.

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The moon and heart health

There is some evidence to suggest cardiovascular systems are most efficient during a full moon, says Clayton. One study on aortic dissection, treated with emergency heart surgery, showed patients had a significantly higher chance of survival if the surgery was carried out during a full moon7. Also, these patients, on average, needed a shorter post-operative stay in hospital - 10 days rather than the usual 14.

There's also a theory that the moon had an impact on our blood pressure. The idea being that if the moon can influence water, it could also affect another major liquid - our blood.

One study investigated physical fitness, heart rate and blood pressure in different phases of lunar month on men8. It found evidence that blood pressure dropped by around 5mm Hg during new moon and full moon phases, when gravity is thought to be at its strongest. Some experts believe that this gravity has a beneficial effect on human circulation.

However, the evidence is far from conclusive, and many other studies have found no patterns between heart health markers like blood pressure and heart rate in relation to the moon's cycles9.

The moon and violence

The image of the man turning in to the aggressive werewolf at the full moon, may be more real that it seems - if anecdotal evidence is to be believed. But Clayton warns that stories from police and hospital staff of aggression around a full moon should be taken lightly. "Despite numerous studies and articles written on the subject, the lack of statistical evidence leaves this feeling like pseudoscience."

Since a 1998 study of prison inmates found a rise in violent incidents during the days on either side of a full moon, many more studies have been conducted. No studies have since produced the same results, and most experts have come to the conclusion that a full moon doesn't result in more incidences of violence, suicide, and aggression. In fact, one study found that homicide cases dropped around the full moons between 1961-201410.

The moon and modern day living

What is making it hard to really know the effects of the moon, is the comforts of modern day living and electric lighting. "Many of us are out of sync with our bodies, and with the natural world around us," says Clayton.

Because we live in a world full of artificial lights, I’m not sure how aware we are of moon phases in our daily lives, or if there are subtle shifts in our emotional states during these times. We don't check in with ourselves frequently enough, so we are often unaware of our wellbeing until our feelings become more extreme.

"The relevance between lunar phases and our emotional, mental, and physical health feels diminished," says the psychotherapist. "We are lacking in self-awareness and are disconnected from nature. Perhaps it's time to start paying more attention?"

Further reading

  1. Francis et al: Psychiatric presentations during all 4 phases of the lunar cycle.

  2. Water Science School: The water in you: water and the human body.

  3. NIH: Bipolar mood cycles and lunar tidal cycles.

  4. Casiraghi et al: Moonstruck sleep: synchronization of human sleep with the moon cycle under field conditions.

  5. Monecke et al: Women temporarily synchronize their menstrual cycles with the luminance and gravimetric cycles of the moon.

  6. Komada et al: The relationship between the lunar phase, menstrual cycle onset and subjective sleep quality among women of reproductive age.

  7. Shuhaiber et al: The influence of seasons and lunar cycle on hospital outcomes following ascending aortic dissection repair.

  8. Chakraborty and Ghosh: A study on the physical fitness index, heart rate and blood pressure in different phases of lunar month on male human subjects.

  9. Chowdury et al: Effects of lunar cycle on fasting plasma glucose, heart rate and blood pressure in type 2 diabetic patients.

  10. Näyhä: Lunar cycle in homicides: a population-based time series study in Finland.

Article history

The information on this page is peer reviewed by qualified clinicians.

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