In some patients with Parkinson's disease, bladder and bowel problems can occur due to the improper functioning of their autonomic nervous system, which is responsible for regulating smooth muscle activity. Some people may become incontinent, and some may have trouble urinating. In others, constipation may occur because the intestinal tract operates more slowly. Constipation can also be caused by being inactive, eating a poor diet, or drinking too little fluid. Medications used to treat Parkinson's disease can also contribute to constipation. It can be a persistent problem and, in rare cases, can be serious enough to require hospitalization.
This answer is based on source information from the National Institute of Neurological Disorders and Stroke.