Which of the following medications is primarily used for lowering cholesterol?

Atorvastatin is primarily used for lowering cholesterol because it belongs to a class of drugs known as statins. Statins work by inhibiting the enzyme HMG-CoA reductase, which plays a crucial role in the biosynthesis of cholesterol in the liver. By reducing cholesterol production, atorvastatin effectively lowers levels of low-density lipoprotein (LDL) cholesterol, often referred to as "bad" cholesterol, and can also help raise high-density lipoprotein (HDL) cholesterol, known as "good" cholesterol. This lipid-modifying effect is vital for reducing the risk of cardiovascular diseases, making atorvastatin a first-line treatment in managing hyperlipidemia.

In contrast, the other medications listed have different primary uses. Metformin is an oral hypoglycemic agent primarily used in the management of type 2 diabetes. Levothyroxine is a thyroid hormone replacement used to treat hypothyroidism. Furosemide is a loop diuretic that is primarily used to treat conditions such as edema and hypertension. Each of these medications has a specific role that does not directly relate to cholesterol lowering, highlighting why atorvastatin is the correct choice for this question.