Actually, thinking about it, does it really make that much difference?
If you get an interview, take the interview and then get an offer, then you're part of their quota of offers. But let's say that you decline their offer. They'll make the offer to person x, from their waiting list.
But, if you decline the interview in the first place, then person y gets the interview. Let's say person y gets in and they accept it, then person x will not get in by virtue of that offer being declined.
In both cases, someone misses out on the opportunity to have an offer to study medicine.