MD PhD program （physician scientist）一起一般是 7 到 8 年， 六年是很少的：

Most MD-PhD students complete the requirement for the dual degrees within 7 to 8 years. Some students complete the program in 6 years, while others may take longer than 8 years. While this initially may seem like a long time commitment, applicants must consider that they are completing academic requirements for two professional degrees to become a physician-scientist. The variation in time to complete the dual degree is due to the time required to complete PhD requirements, since one cannot predict the progress of research, or the amount of time needed to develop into an independent investigator, the primary goal of PhD training. The skills obtained during PhD training are invaluable and will prepare you for a career as a leader of a research group in academic medicine. Note that the average time to complete a biomedical PhD in the U.S. is about 6 years. Thus, if pursued independently, obtaining a dual degree would take about 10 years. By integrating the didactic components of training, dual degree students complete the program in 7 to 8 years on average.

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