The connection between the moon and mood swings is argumentative at best, and little formal research has been done to clearly demonstrate any existing connection. Much of the belief regarding this connection stems from ancient beliefs about the moon as the cause of madness in people and folklore about the phases of the moon. The moon does have a gravitational effect on the Earth, which is clearly seen in oceans and large bodies of water that experience high and low tides. Since the human body has a great deal of water in it, it is possible that this gravitational pull could create a link between the moon and mood swings, but this is hypothetical.
There is a fairly common belief that the moon is linked to mood swings in some way, often pertaining to certain types of moods and certain phases of the moon. Many of these beliefs are tied to old superstitions and folklore regarding the moon as the cause of insanity. The term “lunatic” is derived from the Roman goddess Luna, who was the goddess of the moon and from whom the adjective lunar is derived. Stories of monsters are often associated with night and the moon, such as werewolves and their transformation under the full moon.
While little evidence may exist to support the idea that the moon and mood swings are connected, the moon certainly does have an effect on the Earth. The phenomena referred to as high tide and low tide are created by the gravitational pull of the moon on water on Earth. When a body of water is on the side of the planet facing the moon, it is slightly pulled outward, which causes the water to rise along beaches and shorelines. This effect is heightened during the full moon and new moon, when the sun is also aligned with the moon and the Earth in a state called syzygy, which increases the gravitational push and pull even further.
A great deal of the human body consists of water, which means the moon may pull on water in a person as well, which could create a link between the mood swings and the moon. This is yet to be proven, however, and little research has been done to indicate how a minor gravitational pull on this body water might affect a person’s mood. If the moon and mood swings are connected through gravity, then people should experience mood swings in the same way that water experiences high and low tides. This could be possible, since brain chemistry is extremely complicated, and the syzygy with the Earth, moon, and sun on the full and new moon could then create even more dramatic effects.