[lekanwang]

Yes, this is a very good point -- you're on the clock as soon as you file your patent, so sponsors have an incredibly strong incentive to take risks with trial design and use surrogate endpoints rather than direct endpoints for the primary to cut down on time. Then it's really an educated guess (albeit a highly educated guess) for your Phase III trial design to balance out your market vs chances of proving efficacy.

[refurb]

Patent life is an important factor, but the other one is that it’s sometimes really hard to validate how a drug works. Either you don’t have the technology, money or time to do it. And in the end all that matters is it works in humans.

My favorite story is about gabapentin. Designed to block the GABAase enzyme. It made it all the way to market before they realized it actually works through a different mechanism.