Does the Moon Trigger Bipolar Cycling?

An NIMH researcher explores a novel theory

STUDY: Wehr TA & Avery DH, Molecular Psychiatry 2026 

STUDY TYPE: Observational case series with time-series analysis

FUNDING: Independent

Background

In 2018, Thomas Wehr noticed that mood cycling synchronized with lunar rhythms in bipolar disorder. Dr. Wehr developed dark therapy for mania, so when I saw his paper I thought he must have pinned the cause on the blue light of the full moon. Even today, full moons are linked to psych emergency room visits, and long ago they were responsible for werewolf myths and the unfortunate term lunatic.

But Dr. Wehr had something else in mind: Lunar gravitational tides. The same force that affects ocean waves also alters body temperature, sleep, and circadian rhythms.

Healthy people sleep a bit less and fall asleep a bit later as the moon approaches its full and new phases, a 14.77-day rhythm called the semi-synodic cycle. Since sleep loss can trigger mania, and in this small study Dr. Wehr’s team looked at whether patients with rapid-cycling bipolar disorder react pathologically to this normal lunar sleep rhythm.

The Study

• Three patients with rapid-cycling bipolar disorder whose manic switches recurred near full or new moons, tracked for 122 to 805 days each.
• Daily sleep-onset and sleep-duration records were aligned to each patient’s nearest lunar syzygy and averaged across patients.
• The authors also tested whether mania or sleep disruption came first using cross-correlation and mediation analysis.

Sleep duration shortened by about an hour and sleep onset moved about 40 minutes later as syzygies approached, mirroring the pattern seen in healthy people. In one patient, sleep delay predicted mania days later; in another, mania and shortened sleep were tightly linked the same day. Mediation analysis suggested sleep disruption explained roughly 10% of the mood-lunar link in one patient, with a bidirectional, self-reinforcing pattern in another.

Limitations

Small, selective sample. Mood tracked by diary rather than actigraphy.

Practice Implications

1. Blue light may not be the only reason full moons affect mental health. “There are more things in Heaven and Earth, Horatio, than are dreamt of in your philosophy,”
2. I recommend blue light blocking glasses to deepen sleep, worn 1-3 hours before bed and followed by a pitch dark bedroom. The strategy worked in a few controlled trial of insomnia, and may prevent bipolar episodes as well.
3. To balance gravitational tides… no idea.