Which drug is used to treat diarrhea and is combined with atropine (class V controlled substance)?

• A. Diphenoxylate
• B. Hydrocodone
• C. Apomorphine
• D. Carfentanil

Answer: (A)

Opioid-based antidiarrheal drugs work by activating μ-opioid receptors in the enteric nervous system, which slows intestinal motility and allows more water reabsorption, helping to firm up stools.

Diphenoxylate is the prepare-and-use option that fits this role. It is specifically formulated with a small amount of atropine, which serves as a deterrent to abuse; if someone tries to take much more than prescribed, the atropine produces unpleasant anticholinergic effects (like dry mouth, rapid heartbeat, and potential discomfort), discouraging misuse.

This combination is a Schedule V controlled substance because, when used as directed, it has relatively low abuse potential compared with stronger opioids. The other choices don’t align with the use for diarrhea in combination with an abuse-deterrent: hydrocodone is a stronger opioid mainly used for pain and carries a higher abuse risk, apomorphine is used to induce vomiting, and carfentanil is an extremely potent opioid used in specialized settings, not for treating diarrhea.