I would make the decision based on what you want for undergrad, because you can enter medical school either way. Music majors in general do well with admissions to med school- I once read that as a group they have the highest admit rate of any major (sorry cannot cite anymore).
Have you read the Double Degree Dilemma posted closer to the top of this music forum? I think it would be helpful for you. It I really about the different ways to study music.
A BM will be 2/3-3/4 classes in music a BA will be 1/4-1/3 classes in music. Then there are double degrees, double major, major/minor, and finally, the option of majoring in something else entirely and doing music with lessons and extracurricular activities. BM programs will generally want a portfolio and interview, sometimes audition, for composers. BA programs often have auditions in the fall once you are in: you can submit a music supplement to the common app with recording, resume and letters from music teachers.
What do you want in an undergrad experience? Immersion in music? A broad education with humanities as well as sciences? Check for distribution requirements by the way- some of them are burdensome, and some schools give free choice to students. The latter can provide more flexibility to do music along with something else.
Composers rarely pursue careers after undergrad. Composition is generally a long term proposition, meaning doctorate, though early success can sometimes propel people. Still at least a master’s is often needed, so think about that.
Of course, you can become a doctor and still compose. Or, to put it another way, you can be a composer and still practice medicine!!
Read the essay and look online for the curricula and course requirements at various BA and BM programs. You can certainly apply to BOTH options, or ALL options, and decide in late senior year. Lots can change in the last year of high school.
I know nothing about your experience, resume, or your academic interests so my response is kind of general, but hope it is helpful. Feel free to PM if you like