[refurb]

I think you'd be shocked by how little we understand about the mechanism of action of a lot of the drugs out there.

The FDA's job is to ensure that approved drugs are (1) safe and (2) efficacious. Knowing the mechanism of action (MOA) of a drug can help further define the safety/efficacy parameters for a drug, but in it's absence you can still get a very good sense of the risk benefit analysis.

The best example of a lack of understanding of drug MOAs is Lyrica (epilepsy drug from Pfizer). The drug was designed to target the GABAase enzyme. It got approved and then several years later it was realized that the main MAO is the drug's impact on the glutamate neurotransmitter, an entirely different MOA.