The purpose of the study is to assess how safe and effective the drug Lubiprostone is in people with Multiple Sclerosis (MS)and moderate to severe MS-associated constipation. Lubiprostone is approved by the FDA for the treatment of two common types of constipation in adults, chronic idiopathic constipation and irritable bowel syndrome.

Multiple Sclerosis (MS) is a disorder of the body's immune system that affects the central nervous system. Normally, nerve fibers carry electrical impulses through the spinal cord, providing communication between the brain and the bowel. In people with MS, the covering around the nerve fibers deteriorates, causing nerve impulses to be slowed or stopped. as a result, patients with MS may experiences constipation.

Inclusion Criteria:

• Multiple Sclerosis
• Chronic Constipation defined as < 3 spontaneous bowel movements per week by history and confirmed by diary during the 14 day washout period.
• Women of child-bearing potential must agree to use adequate birth control.

Exclusion Criteria:

• history of other clinically significant medical or psychiatric disorders or suicidal ideation.
• Subjects who have a suspicion of a mechanical bowel obstruction by clinical evaluation prior to dosing that include nausea, vomiting, abdominal pain or distention.
• Subjects with a positive urine pregnancy test prior to dosing.
• Medication changes within one month prior to visit one.
• Corticosteroid use within 2 months prior to visit one.
• Age<18.
• Known intolerance to lubiprostone.
• Inability to perform any required study procedures.