It depends on family contribution of course, as well as undergrad debt, but I'll give you how that number could feasibly be derived [rough numbers]
Lets say $40k undergrad loans
lets say state medical school at 40K/yr x 4 yrs [all loans] = 160k
Pure principal = 200k/ yr. More than 50% is likely to be unsubsidized stafford, so interest has been building for 4 yrs +.
Assume 4 yr residency with deferment BUT interest accumulates. Maybe at overall 6% yr-ish [assuming future hikes in %] = $252,000 in debt by the end of residency.
Paying that off, over the course of 10-15yrs, with interest of course, could easily reach 330,000. Take those numbers and ad up to 100k+ if you went to private university.
NOW, I realize that doesn't account for scholarships, or parental contributions, but from what i gather, most ppl. will not get any of significance. You can see then, that $300-400,000 TOTAL repayment is not out of the ordinary. An ER doc I shadowed was paying over $3000/month and was on a 10 yr plan. He had private undergrad and medical.