The nurse is explaining the differences between uncontrolled and controlled substances. Which of the following medications is a controlled substance?

The correct answer is D: Morphine. Controlled substances, like morphine, have a high potential for abuse and addiction. They are regulated by the government due to their potential harm. Lisinopril (A), Naloxone (B), and Tetracycline (C) are not controlled substances. Lisinopril is an ACE inhibitor used for blood pressure, Naloxone is an opioid antagonist used for opioid overdose reversal, and Tetracycline is an antibiotic. Therefore, the correct answer is D as it meets the criteria for a controlled substance.