Gastrointestinal disorders are the most common non-motor symptoms of Parkinson's disease (PD). They affect the entire intestinal tract and include excess saliva stasis (70% of patients), dysphagia (52%), gastroparesis (34-45%), and constipation. Gastroparesis participates in dyspepsia and abdominal pain. Constipation, as defined by the international standards criteria of Rome III, is present in 59% of PD patients and leads to functional impairment in 70% of patients. The mechanism underlying constipation is multifactorial and may include slow transit and defecation disorders secondary to anorectal dysfunction. Bowel disorders are present in the early stage of the disease and usually precede the onset of motor symptoms. They may result from lesions of the enteric nervous system, of the autonomic nervous system, and from probable alterations in gastrointestinal motility controlled by the central nervous system. The STW5 (Iberogast, Steigerwald, Germany) is a herbal agent composed of nine plant extracts, with prokinetic, antispasmodic, prosecretory, anti-inflammatory and anti-oxidant properties. These properties have been demonstrated in animals and in human pathology, in the treatment of dyspepsia and irritable bowel syndrome. It is the only phytotherapeutic agent which efficacy was demonstrated by randomized double-blind trials in these indications. In PD, the STW5 could improve constipation due to its prokinetic effects of the prosecretory enteric neurons. It could also improve dyspepsia and abdominal pain by its antispasmodic properties. We propose to study the efficacy and the safety of STW5 on bowel dysfunction in parkinsonian patients, especially on constipation.