Robert Califf, commissioner of the US Food and Drug Administration (FDA), said in an interview that misinformation is killing Americans—contributing to the fact that US life expectancy is 3 to 5 years worse than that of people in comparably wealthy countries. He called for better regulation to crack down on misinformation. But would such rules help? I studied medical misinformation as part of a journalism fellowship, and as I’ve written before, there is a real danger when misinformed people skip life-saving vaccines or buy into risky, untested treatments. Yet policing misinformation is tricky.