To test the effectiveness of MNTX in advanced illness subjects.

To determine the efficacy of MNTX compared to placebo to induce laxation in patients receiving opioids.

Inclusion Criteria:

1. Advanced medical illness with a life expectancy of 1 to 6 months
2. No clinically significant laxation within 48 hours prior to the first dose of study drug
3. On stable opioid and laxative regimen for a least 3 days prior to treatment
4. Age greater than 18years
5. Females of child-bearing age must have a negative pregnancy test.

Exclusion Criteria:

1. Females who are pregnant or nursing.
2. Previous treatment with MNTX or prior treatment with naltrexone or naloxone for treatment of OIC
3. Any disease process suggestive of gastrointestinal obstruction
4. Fecal ostomy.