When the patent of a branded drug expires, it falls in the category of Generic drug. Generic Drugs are also known as non-proprietary drugs and do not hold any patent or copy rights. any drug without a patent and copy rights can be manufactured and marketed by any pharmaceutical company. Patented drugs, however, can only be manufactured or marketed by the company which has been granted with the patent and copy rights.
Once a drug is manufactured by a company, the company files a patent to register the drug with FDA which then approves the drug after a thorough test and examination of declares the medicine a property of that particular company. the company can also file a patent for the brand name of the drug. Once patented, no company is allowed to manufacture of market the drug except the company which holds the copy rights. Once the patent expires other companies can also manufacture that drug and sell it.