No, they don't all work out. There sometimes are side effects that make taking the drug counter productive. I would rather not take the anti-nausea drug that would cause my kids to be born with only partial limbs.
And then there are things like the heart medicine that didn't do much for your heart but did have a positive benefit to another organ. :)
Sometimes they error too much on the side of caution. But they do try to get it right.
It's actually only 8%.