The US Food and Drug Administration calculated that drug cost per day can fall by 14 - 16% if patients use generics where appropriate instead of branded drugs.

Patients whose needs can be fully satisfied with generics could enjoy reductions of 52% in the daily costs of their medication.

References:

• United States Food and Drug Administration. Generic drugs: what you need to know. [online] 2002 [cited 2007 Jul 09]. Available at: http://www.fda.gov/fdac/features/2002/502_generic.html
• United States Food and Drug Administration. Savings from generic drugs purchased at retail pharmacies. [online] 2004 [cited 2007 Jul 09]. Available at http://www.fda.gov/cder/consumerinfo/savingsfromgenericdrugs.htm
• United States Food and Drug Adminstration: Office of Generic Drugs. [online] 2007 [cited 2007 Jul 09]. Available at: http://www.fda.gov/cder/ogd/
• SA Medicines Control Council. Guidelines on generic substitution. Government Gazette 2003;25145:183-5.