Relistor (Methylnaltrexone Bromide) is a special narcotic drug that blocks certain effects of other narcotic medicines. Methylnaltrexone Bromide reduces constipation caused by narcotic medications that are often used to treat pain in people with terminal illness. Methylnaltrexone works by preventing this side effect without reducing the pain-relieving effects of the narcotic. Relistor is usually given after laxatives have been tried without successful treatment of constipation.