Which of the following adverse reactions is associated with both Meperidine and Fentanyl?

The correct answer is dry mouth. Both Meperidine and Fentanyl are opioid analgesics that can lead to the side effect of dry mouth, technically known as xerostomia. This occurs because opioids can inhibit the salivary glands' ability to produce saliva, resulting in reduced oral moisture. It's important for healthcare providers to be aware of this side effect as it can significantly impact a patient's comfort, potentially leading to difficulties in swallowing and an increased risk of dental issues.

In contrast, headaches are not commonly associated with either Meperidine or Fentanyl as a direct side effect. Severe allergies, while a serious concern with many medications, are not commonly seen with these two opioids. Increased appetite is not typically a side effect associated with opioid use; in fact, opioids often lead to decreased appetite or nausea. Understanding the side effects of these medications helps ensure better patient care and management of potential complications.