For example, diabetes mellitus may cause constipation or diarrhea. Colorectal carcinoma may also cause constipation, especially when the tumor mechanically obstructs the bowel lumen or metastasizes to the spinal cord. Colorectal carcinoma may be suspected when the constipated patient also experiences abdominal discomfort, gaseousness, weight loss, malaise, tenesmus, and notices blood in the stool. Medications are another secondary cause of constipation. Secondary constipation can also be caused by laxative dependence.
Laxative misuse can induce perceived constipation.
A patient may be convinced of the necessity for a single daily bowel movement. To reach this goal, he or she might ingest a harsh laxative, such as senna, bisacodyl, castor oil, or casanthranol. Unfortunately, these laxatives do not induce a normal bowel movement. This is the reason why laxative-induced bowel movements often contain semisolid stools with more liquid than normal. The patient is pleased with the large volume of stool.