Before 1962, a new drug in the United States only had to be safe. Amendments passed that year added a second test. The FDA must find that a drug is both safe and effective. The proof must come from “adequate and well-controlled investigations, including clinical investigations.” Experts must be able to conclude that the drug “will have the effect it purports or is represented to have.”

The law does not ask how the drug works. Derek Lowe writes on drug research. He states: “There is, in fact, no requirement that a new drug’s mechanism of action be known at all.” The diabetes drug metformin reached the market without a known mechanism. Its mechanism is still debated.