Alimta belongs to a group of medications known as folate analog metabolic inhibitors. It works by preventing the conversion of folic acid into its active form. The active form of folic acid is used by cells to make DNA and RNA -- important molecules essential for cell division.

Alimta is more likely to affect cancer cells than healthy cells. However, as with most forms of chemotherapy, some healthy cells will be affected, and this process is likely responsible for many of the side effects of chemotherapy.