Patient description: A 57-year old farmer was diagnosed with Parkinson's disease a year ago. He experiences slowness of movement and tremors. His past medical history is significant for hypertension and hypercholesterolemia. He lives with his wife. They have three children. He used to be active with planting and taking care of their farm animals before his diagnosis. The patient complains of shaking and slow movement. He had difficulty entering through a door, as he was frozen and needed guidance to step in. His handwriting is getting smaller. He is on Levodopa and Trihexyphenidyl. He stated his medications help with shaking and slow movement. But he still has difficulty initiating movements, stiffness and slowness in general. He is an alert and cooperative man who doesn't have any signs of dementia. He doesn't smoke or use any illicit drugs.

Clinical trial eligibility criteria: eligible ages (years): 18.0-85.0,  Parkinson's Disease Subjects must be diagnosed with PD according to conventional criteria Subjects must report having constipation and fulfill Rome III criteria19 for chronic constipation: at least 3 months, in the last 6 months with two or more of the following: i. Less than 3 SBM's per week ii. Straining with defecation more than 25% of the time iii. Lumpy or hard stools with defecation more than 25% of the time iv. Sensation of incomplete evacuation with defecation more than 25% of the time v. Sensation of anorectal obstruction or blockage with defecation more than 25% of the time vi. Use of manual maneuvers to facilitate defecation more than 25% of the time Patients will be encouraged to use only lubiprostone for constipation. If they use any other agents they will need to record this use in their diary; any BM that occurs within 24 hours of the other agent used will be recorded, but not be counted as a SBM Patients or patients' caretaker(s)/ legal guardian must be able to read, understand, and accurately record data into the diary to guarantee full participation in the study Patients over the age of 50 must have had a colonoscopy or sigmoidoscopy within 5 years Patients or patient's caretaker(s)/legal guardian must be willing and able to provide informed consent before beginning the study  Evidence of structural abnormality of the gastrointestinal tract or diseases/conditions that affect bowel transit including gastric, small bowel or colonic resection (appendectomy, cholecystectomy, benign polypectomy are allowed); history of colon cancer, history of inflammatory bowel disease (Crohn's disease or ulcerative colitis); insulin-dependent diabetes mellitus, history of Hirschsprung's disease, progressive systemic sclerosis (scleroderma), anorexia nervosa; other diseases or conditions that in the opinion of the investigator significantly affect bowel transit. Subjects with constipation secondary to any other documented cause Planned use of drugs or agents during pretreatment phase onward that affect gastrointestinal motility and/ or prescription including laxatives including stool softeners (patients experiencing significant constipation may use a laxative as rescue medication if needed); antidiarrheals (in case of significant diarrhea loperamide may be used if needed); antacids containing magnesium or aluminum salts (only calcium containing ones are allowed); anticholinergics, antispasmodic agents (e.g., Librax, Donnatal, dicyclomine); erythromycin and other macrolides; octreotide; ondansetron or other 5-HT3 antagonists; opioids/narcotic analgesics; prokinetics (metoclopramide); serotonin re-uptake inhibitors or tricyclic antidepressants (allowed if constant doses for at least 1 month before treatment); calcium antagonists (allowed if constant doses for at least 1 month before treatment) Subjects with any significant cardiovascular, liver, lung, renal, psychiatric or neurological diseases (not including PD) Patients with previous allergic reaction or lack of tolerability to lubiprostone Current or recent history (within 12 months) of drug or alcohol abuse Pregnancy or breast feeding Fertile women (defined as those who are not surgically sterile, are not >1 year post-menopausal or who are not currently using or complying with a medically approved method of contraception). Lubiprostone has not been studied in pregnant women and should only be used during a pregnancy if the potential benefits justify the potential risk to the fetus. Women should have a negative pregnancy test before beginning treatment with lubiprostone and need to practice effective contraceptive measures