Hey there,
I am a PhD student at BU Med. A year after taking classes and finding a lab, etc, I realised that I also wanted to attend medical school. Here is what the BU office told me:
1) They accept MDs into the MD/PhD program, but not PhDs into the MD/PhD program. So you would have to quit your degree and apply to the MD/PhD program without being enrolled as a student. The tricky thing about this is, if I had done that there would be no way that BU Med would have accepted me. They don't give chances to people who bite the hand that (literally) feeds them.
My advice: If you are already into a PhD program, finish it or leave with a Masters, then apply to medical school. You can certainly take the MCAT at any point, and you can apply to other MD/PhD programs as well. I am not sure what are the guidelines at your particular institution in regards to this matter, but at BU if I had applied to the MD/PhD program they would have rejected me right away because I am an enrolled PhD student.
In terms of finances, doing a MD/PhD program is the best way to have less debt at the end. However, there are other options such as attending state schools, applying for outside funding, etc. Although money is a huge issue, don't let that be THE main reason why you want to do that. I would feel pretty crappy about myself if I had left my PhD program to pursue an MD/PhD somewhere else, but that is mainly because I love my department at BU and I am happy there as a PhD student. Talk to the admissions office at your school and weigh your options. Best of luck!
