American here. advice above is all valid but I'll try to add to it:
• US uni's are gonna want a SAT/ACT, esp for the competitive ones as an international student.
• "pre-med" isn't an actual major, just something kids call themselves amongst themselves to make themselves feel more competitive–you'll find for every 5 kids that begin ugrad as "pre-meds" maybe 2 actually sit the MCAT and maybe 1 will actually get an offer and attend, and that's at better US unis. you just need the pre-reqs in bio, chem, orgo, physics, and I think maybe english or maths to apply.
• omg it costs way more, google the tuition rates for wherever you're considering. also consider which state you have legal residence in, and whether the top public uni / med school there is somewhere you'd attend (all US MD programs are nxt lvl they're just diff).
• after 2nd year but before applying AMCAS/AACOMAS you need to take MCAT and ideally score in 90th+ percentile to have a chance at US MD programs. there are also DO programs which will make you just as much a Dr. but usu for less competitive specalties plus less of a research-focus and you have to learn osteopathic manipulative medicine [which realistically very very few actually utilize professionally].
• honestly, it's a lot more competitive than UK medical schools, as far as any MD programs go. I would say DO is perhaps on par with GEM here. applied to US MD schools twice with a single offer I couldn't take, and applying now to 5yr A100's and its straight up just night and day. google average GPAs and acceptance rates at any US med school, there's a reason most candidates apply to anywhere btwn 10 and 30 schools…
• straight up, you better have money to blow btwn ugrad and med school tuition [even after financial aid and scholarships], but there's always that carrot dangling that you'll make significantly more in salary one day as well. don't even consider if you're taking out loans to do it and have to pay back interest.
any more Qs/advice can DM me. all the best.