In New Zealand and Australia, undergraduate students can pursue an M.D. or MBChB which gives them a professional certification in medicine. What is the situation in the US?
In the US, Medicine is a post-graduate degree only, meaning you must study a 4 year undergraduate degree before applying. Entry into Medical Schools in the US is based on your Undergraduate GPA, your MCAT results and an interview.
Once accepted, medical school in the US is a 4 year degree, meaning a total of 8 years study until you become a doctor. While this is longer than NZ and Australia, the process of becoming a specialist doctor is faster in the US, taking 2-4 years from graduation as opposed to 7-10 years in NZ and Australia.