(CNN) -- Lipitor, the popular cholesterol-lowering drug, loses its patent Wednesday, paving the way for cheaper generic versions.
"For generic drugs, they have the same active ingredient as the brand-name drug and the big difference is they tend to be significantly less expensive," said Dr. Glen Stettin, chief medical officer of Medco, one of the country's largest pharmacy benefits manager.
More than 17 million people have been prescribed Lipitor, according to its manufacturer Pfizer. Last year, Lipitor's sale added up to more than $5 billion in the United States alone, according to Medco.
While it is not known how much cheaper the generic version of the cholesterol-lowering drug will be, Pfizer is working with pharmacy benefit companies to lower co-payments to hold on to as many customers as possible.
When drug companies develop a drug, the Food and Drug Administration usually grants them exclusive rights to market the drug for a set period of time.
When those rights expire, other companies can make same drug. The competition results in cheaper generic versions.
The FDA says the regulations are "designed to promote a balance between new drug innovation and generic drug competition."