Drugs die for all sorts of reasons other than being ineffective. A major one is the cost of getting a drug approved is now so expensive that you can’t make money off it. The vast majority of diseases are effectively beyond treatment because the market for them is not large enough to support the cost of developing a new drug for them.<p>The other major reason for failure at Stage I&#x2F;II is that the preclinical models we are using are not a good match for human disease. This means that a drug that works in a mouse model can’t ever work in humans because the mouse model does not reflect the human disease (Alzheimer&#x27;s is the classic for this). We are using preclinical models we know are useless and are then surprised when the drugs found using them don’t work in humans.