Others however argue that the patent system encourages inefficiency and can reduce innovation as firms can continue to earn supernormal profit on previous innovations. For this reason most patents, particularly in high tech industries and biomedical sciences are time limited. They also argue that patents allow firms to charge higher prices and therefore they reduce the welfare of those who purchase treatments (individual patients or national health providers). Finally critics of the patent system argue that they stifle innovation by reducing the spread of information and limiting cooperation. Boldrin and Levine argue that the current patent system is so complex and full of perverse incentives that abolishing the patent system and allowing free competition would actually enhance innovation