Do BS/MD programs care about your major in college? The answer really depends on the specific BS/MD program.
There are many programs, particularly eight year ones, that allow students to have any major. Brown University, Case Western Reserve University, and Hofstra University are a few examples of 8 year BS/MD programs with open majors. But not all 8 year programs allow any major. Union College‘s Leadership in Medicine program requires students to major in biology, chemistry, physics or math as well as have a second interdepartmental major in the humanities or social sciences. Siena College requires a major in biology and a minor in the humanities. On the other hand, George Washington University allows students to major in a variety of subjects even though they are a seven year program.
It is fairly common that the seven year programs require a specific major, typically one of the sciences, for those students in a BS/MD program. This is because medical schools require a number of classes before attending the medical school and in the three years of undergrad during a seven year program, it can be difficult to have enough time to complete a major other than a science one.
Somewhat surprisingly, the University of Missouri Kansas City, one of the few remaining six year programs, allows students to major in biology, chemistry or liberal arts.
The bottom line is that if you have a specific major you want to have, you have to investigate each program closely to make sure that your major will work with that BS/MD program.