The investigators will recruit a total of 136 diabetic men and women with constipation into this study from both The Emory Clinic and The Atlanta Veteran's Administration Hospital. The investigators will track spontaneous bowel movements defined as a bowel movement in 24 hours after initiation of study drug (SBMs) in all patients two weeks before treatment with lubiprostone as well as measure baseline colonic transit using the Smartpill pH capsule. Colon transit reflects that rate of colonic peristalsis and movement of stool through the large bowel.