Hi Merri Ellen, I never thought of why, but it is true that antidepressants and pain medicine cause bowel problems, especially constipation. This is one of their side effects. I don't know if the new SSRI's (zoloft, prozac, etc) are as bad, but the old antidepressants (tricyclics such as elavil, imipramine) cause major constipation. (as well as other "drying out" problems such as dry mouth) I have even heard some people say that nonsteroidals (ibuprofen, Alleve, etc) constipate them, but narcotics are known to turn your bowels to cement. I'm not sure if the reason they do this is the same as the antidepressants.
chris S.