Echoing all the other statements: You app taken as a whole (you as a whole) will determine whether or not an adcomm likes you enough to let you in the gates. I am sure there are thousands of single majors (me, for instance) who had their choice of medical schools. Make sure your whole app is good. The adcomms may notice you more if you have a double major, but they also may take notice if you started a free clinic or won a prestigious award, or did some really cool undergrad research, or came from a certain background, or can speak other languages, etc., etc. Who knows what any one adcomm is going to pick out of your app that speaks to them in some way. Do the double major only if you think it will enrich your undergrad years and make you happy. Otherwise, minor in the other subject that you would have doubled in, and take the "free" time you'll have to do more ECs or spend more time with family, friends, etc. Good luck!