FDA's Kelsey stalled thalidomide by declaring it incomplete

Under 1960s FDA rules, a New Drug Application was automatically approved for market if the agency's reviewer failed to formally reject it within 60 days of submission — a structure that put the burden on a reviewer to actively stop a drug rather than requiring the manufacturer to actively prove safety, meaning inaction by the FDA defaulted to approval, not caution.

Kelsey found the clinical safety data Merrell submitted unconvincing rather than clearly conclusive — not proof the drug was dangerous, but not proof it was safe either. Rejecting the application outright against a well-funded, aggressive pharmaceutical company with only ambiguous evidence risked a fight she might not win under a regulatory structure built to favor approval by default; Merrell's sales representatives began pressuring her office directly once the delay began.

She stalled by declaring each submission incomplete, resetting the clock, so she never had to prove harm—only that the data fell short of the legal bar.

Each incomplete ruling reset the clock, so the application never reached automatic approval.

The company couldn't overturn a legitimate procedural hold, so pressure on Kelsey's superiors failed.

The delay let independent evidence of birth defects surface, turning a stall into a permanent block.

When a process defaults to an outcome you distrust, use its own procedural requirements to stall, rather than fight the default head-on.

Kelsey's repeated requests for better evidence delayed thalidomide's US approval for roughly 19 months, during which independent researchers in Germany and Australia established a clear link between thalidomide and severe birth defects, affecting an estimated several thousand babies born to mothers who had taken the drug in Europe and elsewhere. Thalidomide was never approved or marketed in the United States, sparing American mothers and infants from the disaster unfolding abroad.