Upon discharge, which medication should a patient on oral morphine also receive to manage potential side effects?

When a patient is on oral morphine, one of the common side effects is constipation due to the opioid's effect on the gastrointestinal tract. Opioids like morphine slow down gut motility, leading to decreased bowel movements and increased water absorption in the intestines, which causes harder stools.

Senna is a stimulant laxative that works by stimulating bowel contractions, making it a suitable adjunct treatment for managing opioid-induced constipation. Including senna upon discharge aids in preventing or alleviating constipation, allowing for more comfortable bowel habits while the patient continues to take the opioid.

The other options do not specifically address the most significant side effect of morphine. Diphenhydramine is an antihistamine, commonly used for allergies or to aid sleep but is not indicated for opioid-related side effects. Methylphenidate is a stimulant used to treat attention deficit hyperactivity disorder and does not correlate with managing side effects of morphine. Docusate sodium is a stool softener, which can help with constipation but is generally less effective than senna for stimulating bowel activity. Therefore, senna is the most appropriate choice to support management of constipation associated with morphine use.