CONSTIPATION can occur from taking iron, from the manipulation of the bowel during surgery, from lack of fiber in the diet, from dehydration, from decreased activity, and from taking certain pain medications especially opioid derivatives. Some medications given for opioid constipations are: Amitiza oral, Relistor subcutaneous, lubiprostone oral, Movantik oral, methylnaltrexone subcutaneous, naloxegol oral