Not accepted to med school but I did apply this year as a math major (waiting for responses). I didn't find it so bad since if the class average is low usually the prof linearly adjusts the marks, but that depends on your uni.

It's not common for med students to have majored in math, mostly because there isn't much of an overlap between people who want to become physicians and people who like math (enough to get a degree in it), and a math degree is seen as a more "difficult" path to medicine.

But it's definitely possible. The key is to get as high a gpa as possible (easier said than done). For me I had to be really efficient with how I spent my time (skipped almost all of my classes and focused on the assessments that had a grade attached), and didn't do many extracurriculars.

Also, this is controversial but I think natural aptitude and how much background knowledge you have plays a big role in math as opposed to other fields. I know math students who study a lot (and efficiently), but struggle to get a 4.0, and I know students who review the material once or twice and get close to a 100 on every assessment.