A warning issued by the United States surgeon general, Dr. Vivek Murthy, on Tuesday provided guidance about an issue that has been front of mind for American parents for years: the negative effects of social media on the mental health of young people.

These types of public health advisories are infrequent, but sometimes become turning points in American life.

Cigarettes

It took a surgeon general’s report in 1964 and decades of effort that followed for smoking in America to go from being seen as a glamorous habit to one with deadly consequences.

The annual per capita cigarette consumption in the United States had increased from 54 cigarettes in 1900 to more than 4,000 cigarettes in 1963 when the first research suggested links between smoking and cancer.

That prompted Dr. Luther L. Terry, the surgeon general under Presidents John F. Kennedy and Lyndon B. Johnson, to issue a landmark report on the health hazards and consequences of smoking in 1964.

Dr. Terry described the crisis as a “national concern.”

The fallout was swift. In 1965, Congress required all cigarette packages distributed in the United States to carry a health warning. In 1970, cigarette advertising on television and radio was banned.

AIDS

Dr. C. Everett Koop, the surgeon general under President Reagan, was credited with changing the public discourse around the H.I.V./AIDS epidemic during the 1980s. In 1986, he issued a generation-defining report on AIDS. In plain language, the report discussed risk factors and ways that people could protect themselves, including the use of condoms for safer sex.

But frank discussion of sexual topics later tripped up a surgeon general who served under President Bill Clinton, Dr. Joycelyn Elders. Although her efforts to expand access to health screenings and sex education were praised by some, she resigned under pressure in 1994 after she proposed the distribution of contraceptives in schools and condoned teaching children about masturbation as a way to prevent the transmission of H.I.V., among other views that drew the ire of conservatives.