Can any medicines unintentionally change the way your poop comes out?

Yes: Medications/drugs can change gastric motility, digestion, and impact the way your body processes wastes & as a result can cause stools to be soft, liquid, hard, different color, and so on depending on the drug or medication. Most meds/drugs as a common side effect will loosen stools or cause mild hardening which are not anything to worry about & temporary. Pain meds usually need a stool softener.