In declaring the opioid epidemic a public health emergency last week, President Trump promised that the federal government would start “a massive advertising campaign to get people, especially children, not to want to take drugs in the first place.” But past efforts to prevent substance abuse through advertising have often been ineffective or even harmful.

Perhaps the most famous American antidrug advertisement featured a sizzling egg in a frying pan to the sound of ominous music and a stern voice-over warning, “This is your brain on drugs.” A sequel to this ad featured Rachael Leigh Cook smashing an egg and the better part of a kitchen to dramatize the impact of heroin.

Many other ads denouncing drugs and emphasizing their destructive effects — as in the “Just Say No” campaign — appeared regularly on television and in print beginning in the 1980s. Most of them were funded by the White House Office of National Drug Control Policy, which received hundreds of millions of dollars a year from Congress for such campaigns.

Visually dramatic though the ads were, evaluations of them were deeply discouraging. The billions spent from the late 1980s through the mid-2000s at best had no effect on drug use, research shows. At worst, exposure to the campaign might have actually increased the likelihood of adolescent marijuana use. A study of over 20,000 youths 9 to 18 found that those who had been exposed to more antidrug ads expressed weaker intentions to avoid marijuana and more doubts that marijuana was harmful.