Like my main focus would be pre-med but I also want to study religion.
In college, the process varies but you usually can declare either a dual degree or double major. The difference is a double major still requires about the same amount of credit hours as your primary major but that's because the majors are connected in some way (ex. business and economics, math and physics). You will graduate with a Bachelor's in X and Y. A dual degree is more credits, so it takes longer, but you get two separate degrees - this is if you have completely unrelated majors like dance and engineering, or like in your case, pre-med and Islamic studies. So it'll be a Bachelor's in X and a Bachelor's in Y. If you're applying and can list a second major, certainly do it; if you're already in college or when you get there, talk to advisors.
However, I would like to ask - why do you want to do Islamic studies? Is it a passion or does it also relate to your career intentions? I see this being a good choice if you, for example, want to do medical work in an Islamic country. If you're just interested in studying Islam, I would either do it on your own time or (like the other person said) take it as a minor.
You could major in pre-med and minor in Islamic studies. I think this would be the best option. You could also double-major in both pre-med and Islamic studies.
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thank you also can i ask what is the difference if I major in pre med and minor in islamic studies vs double major?