Patent evergreening is a strategy mostly adopted by pharma companies. In this strategy, the pharma companies that have patent rights that are about to expire, try to renew their patent in order to keep that particular patent alive and make more money out of it. There are many strategies that they can adopt such as filing new patent applications with minor changes, substituting chemicals with new chemicals that would have similar effect and so on. Pharma companies adopt these strategies on highly valuable patents that provide huge profit margins. These companies intend to prolong the life of a patent further than 20 years in order to gain profits for a very long time. The ultimate aim is to prevent the generic drug making companies from entering the market as long as permissible so that the drug is highly priced even after the expiration of the patent protection period.