I would like to add some information to that provided by Henry. The (undergraduate) medical education lasts for four year, and in order to get into medical school you need to have a bachelor degree in any field and you should have taken the required prerequisite courses. The requirements vary from college to college but definitely you need credits in undergraduate physics, general (or inorganic) chemistry, organic chemistry, and biology. Some of the schools also require credits in english, and or mathematics. After the four year of undergraduate medical education you have an MD but can't practice in the US. You should go for a residency program in order to specialize in certain field. For an anesthesiologist the program lasts for your years. During the residency you get a payment that averages $50k/year.