**Core Concept**
The question tests the student's knowledge of pharmacological side effects, specifically focusing on drugs that affect gastrointestinal motility. Constipation is a common side effect of certain medications that alter the normal functioning of the gut.

**Why the Correct Answer is Right**
Unfortunately, without the actual options provided, a general approach would be to identify drugs known to slow gastrointestinal motility or affect water absorption in the intestines, such as opioids, anticholinergics, or certain antacids.

**Why Each Wrong Option is Incorrect**
**Option A:** Without specific details, a common incorrect option might include a drug that is known to cause diarrhea, such as laxatives or certain antibiotics.
**Option B:** Another incorrect choice could be a medication that has no significant effect on bowel movements.
**Option C:** This might include a drug that is actually used to treat constipation.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that opioids are well-known to cause constipation due to their effect on the mu-receptors in the gut, which reduces peristalsis.

**Correct Answer:** D. Opioids.