Only you can answer if it’s a good idea or not. Is econ what truly interests you, more than biology? If so, I would switch.
For medical school, it doesn’t matter what your major is. You just need to complete prereq courses to be eligible. Many premeds choose a major like bio because it fulfills most of the prereqs in its major requirements, but there’s absolutely no rule that says you have to do that. If anything, it’s better to major in something that you’re truly interested in and can (hopefully) get a higher GPA in while taking the prereq classes. If biology is your true interest, then major in that; if it isn’t, then major in whatever your interest is.
I don’t know much about the econ majors, so I can’t give any specific recommendations there. I would read program descriptions and requirements to determine which one sounds more interesting to you: [url = <a href=“http://catalog.ucdavis.edu/programs/ECN/ECNprog.html%5DEcon%5B/url”>http://catalog.ucdavis.edu/programs/ECN/ECNprog.html]Econ[/url] [url = <a href=“http://catalog.ucdavis.edu/programs/mecon/meconprog.html%5DMan”>http://catalog.ucdavis.edu/programs/mecon/meconprog.html]Man econ
Just from looking at the requirements for both, man econ is more unit-heavy and has more that you may need to catch up on. Econ has a lower unit count and would be easier to catch up on requirements. You’re still early enough where you should be able to choose either and still graduate in 4 years though; it’s more a question of how flexible your schedule would be. Talk to advisers if you’re unsure.