Because the research and development of new drugs requires a lot of capital investment, there are high risks. In order to protect the enthusiasm of pharmaceutical companies to develop new drugs, the state will protect the new drugs developed by pharmaceutical companies for a certain period of time. During the protection period, only the manufacturer of the original drug is allowed to sell the drug, so as to obtain enough profits to make up for the investment in research and development of new drugs. At present, sildenafil citrate is in the protection period, and only Pfizer can produce it.