Patent is the right to ownership,as part of an intellectual property law, where by a person / organization discovers a lesser known concept or invents something new and holds sole intellectual ownership rights to that particular idea. These are usually published / granted after a lot of research and exhaustive verification. Patents are generally registered with United States Patent and Trademark Office, an Agency Of The United States Department Of Commerce, in the United States and The Intellectual Property Office,a division of the Department for Innovation, Universities & Skills in the United Kingdom.
Pharmaceutical patents protect manufacturers of prescription drugs, prohibiting others from producing a drug during the length of its patent protection. The length of these patents varies in different countries, though they are usually between 15-20 years. In the U.S., a pharmaceutical patent is valid for 20 years. Drug companies usually apply for patent protection before they actually begin producing the drug, opting instead to secure their rights to a particular compound at the beginning of the testing process. By the time a drug comes to market, there may only be 8-10 years of patent protection remaining, which is significantly less than the 20 offered by the patent. Companies often attempt to extend these patents by making slight reformulations of the original compound or proving its effectiveness at treating a condition other than the one for which it was originally granted a patent. This is referred to as "evergreening", a practice which many criticize.
For more information about pharmaceutical patents in relation to generic versions of drugs, see Generic Drugs.