Proprotein convertase subtilisin/kexin type 9 (PCSK9) is an enzyme that binds to low-density lipoprotein receptors (LDL receptors), which stops LDL being removed from the blood, leading to an increase in blood levels of LDL. The PCSK9 inhibitor blocks the PCSK9 enzyme, resulting in more LDL receptors available to remove LDL from the blood, which produces in a decrease in LDL blood levels.