The aim of this pilot study is to investigate the effect of Osteopathic Manipulative Medicine (OMM) in decreasing constipation symptoms in people with Parkinson's disease (PD). A second but optional aim is to determine if OMM changes the bacterial flora of the mouth and gut. OMM is a safe and gentle manual treatment provided by osteopathic physicians. All participants will receive OMM during the second half of the eleven week trial.