If I recall my stats correctly, there is approximately <historically -- it will vary by individual schools> a 10% loss rate prior to the second year. However, of those who make it to the second year, there is approx a 98% graduation rate.
In short, there is no guarantee that you will become a Doc by simply getting in...you also have the fun & frolic of the board exams...all 3 steps.
For step 1 <both COMLEX & USMLE> there are set maximum attempts that you may take before passing. I believe there is a "national" limit of 6 attempts; but some states limit it to 3. Recently, the FSMB recommended that all states adopt a 3 or 4 try limit for all steps. That means, if you don't pass in 'X' number of tries, you'll never get a license in certain states. These limits may also apply to all 3 steps of both boards...of that, I am uncertain.
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'Old Man Dave'
KCOM, Class of '03
Nothing Risked, Nothing Gained!!