Which of the following medications is considered a calcium channel blocker?

Amlodipine is considered a calcium channel blocker because it works by inhibiting the influx of calcium ions into vascular smooth muscle and cardiac muscle. This results in relaxation of the muscles, leading to vasodilation and a decrease in blood pressure. Calcium channel blockers like amlodipine are primarily used to treat hypertension and certain types of angina.

The other medications listed serve different purposes and fall into other categories of pharmacological agents. Lisinopril is an ACE inhibitor that helps manage high blood pressure and heart failure by preventing the conversion of angiotensin I to angiotensin II, which causes blood vessels to constrict. Warfarin is an anticoagulant that works by inhibiting vitamin K-dependent clotting factors to prevent blood clots. Clonidine is an alpha-2 adrenergic agonist that reduces sympathetic outflow and is utilized in the treatment of hypertension by lowering heart rate and blood pressure. Thus, amlodipine stands out as the medication specifically classified as a calcium channel blocker.