The Iowa state ban on the use of thimerosal in almost all vaccines used on children became effective. Iowa, passed the law on 14 Apr 2004, and became the first state in the U.S. to enact such restriction. California followed in 26 Aug 2004. State politicians reacted to public concern. Thimerosal contains ethylmercury, a compound of mercury. In other circumstances, mercury is known to be a toxic substance. However, thimerosal had been used in microgram quantities in vaccines to prevent bacterial contamination since the 1930s. On 9 Jul 1999, the Centers for Disease Control and Prevention and the American Academy of Pediatrics, merely as a precaution, asked pharmaceutical companies to discontinue its use in vaccines as soon as possible, though medical evidence was otherwise reassuring.«

Effective on this day, all US cigarette packages began carrying the health warning: Caution: Cigarette smoking may be hazardous to your health. This resulted from landmark federal legislation enacted in 1965 that required health warnings on cigarette packages. In 1984, the law was amended to require one of four warning labels in most cigarette-related advertising (U.S. Code, Title 15, Chapter 36, Sec. 1333.)