Final answer:
Toprol XL (metoprolol) can lead to bradycardia as it is a beta blocker that slows the heart rate by inhibiting beta-1 receptors, which are normally bound by norepinephrine.
Step-by-step explanation:
Toprol XL (metoprolol) is known to cause bradycardia. This medication belongs to a class of drugs known as beta blockers, which work by blocking the beta-1 receptors. NE, or norepinephrine, binds to these receptors, and beta blockers like metoprolol inhibit this binding. By doing so, they slow the heart rate (HR) and can be used to treat hypertension. However, overprescription or high dosages of these medications can lead to excessively slow heart rates, known as bradycardia, and in severe cases, may even lead to stoppage of the heart.