However, because gefapixant was only marginally more effective than placebo in treating unexplained or refractory chronic cough, the Food and Drug Administration (FDA) did not approve the drug.

Merck filed for approval of gefapixant in March 2021 on the strength of a pair of phase 3 trials – COUGH-1 and COUGH-2 – which found that the drug reduced 24-hour cough frequency by 18% and 15 ...