There will be people out there that are severely allergic to the compound. You can do a trial of one million patients with all kind of co-morbidity and numerous drug interactions. Darn, the one million and one patient taking an obscure drug then has a serious reaction to the drug. Don't be so negative. I don't Merck is being evil. This is not a reflection of sloppy work.
Or you can bury study data or just write fake papers