This study is being done to learn if yohimbine, a naturally occurring drug, affects the speed
at which food travels through the stomach, intestines and colon, and if yohimbine affects the
amount of liquid you can drink in a short period of time. Understanding how yohimbine works
on the gut may help develop new treatments for patients with constipation. Yohimbine has been
approved by the Food and Drug Administration (FDA) for routine clinical use, however, its use
as proposed in this study is considered investigational.