I don't know the details of the nexium approval but for novel drugs you don't know it's effective until you test it The biggest driver of the high cost of drug

I don't know the details of the nexium approval but for novel drugs you don't know it's effective until you test it The biggest driver of the high cost of drug development are failed late stage (phase 2 and 3) studies. Things look effective in the lab, then look effective in animals, then look potentially effective in exploratory human studies, then when you test rigorously for effectiveness in humans, they often fail. And these late stage human studies are the most expensive For generic drugs where you "know" it is safe and effective, there's an expedited pathway with fewer / smaller studies. And for slight tweaks to approved drugs there is another process that's more burdensome than the generics approval process but not as bad as a full new chemical entity path