Are you on narcotic pain killers? These slow down the intestines and bring on constipation. I found the most effective thing for me was to take a dose of metamucil or equivalent with each dose of methadone. If I expected trouble I'd take a little senecot the night before (it's in several of the laxatives). As a last resort or if you miscalculate there are the stool softeners. If all that doesn't work I'm not sure what's next.