I have heard many times before that people with mental disorders become hyperactive during the full moon. I have never believed it, but has there been any scientific study carried out to prove it one way or the other?
Such studies actually exist. The Skepdic entry for Full moon and lunar effects gives a full list of things that have been studied, but in particular there was insufficient evidence to support that the following correlate with a full moon (that means that such a correlation doesn’t exist):
- psychiatric admissions [one study found admissions were lowest during a full moon]
- behavioral outbursts of psychologically challenged rural adults
All of which are different effects of mental illness. The list comes from the 1996 review by Kelly, I. W., James Rotton, and Roger Culver, The Moon was Full and Nothing Happened: A Review of Studies on the Moon and Human Behavior and Human Belief