Today, with youth opioid use falling, America may be at another inflection point. “Quite often, drug epidemics follow a classic curve,” said Samuel K. Roberts, an associate professor of history and of sociomedical sciences at Columbia University, describing how they seem to start slowly, spike and then fall.

One reason for this pattern may be the rising visibility of harm associated with use, both in the media and, probably more important, among family and friends. “What makes it subside is usually a number of things,” said Dr. Roberts, “but one of them is often that the negative perception of a particular drug will take off.”

That seems to be happening with opioids now, given the extraordinarily high death rate. There is no fentanyl chic; the drug is publicly associated with sudden death, homelessness and skin infections, not fun.

“Most younger people, they’re very much concerned,” said Jeremy Sharp, the operations director for Students for Sensible Drug Policy, which organizes youth to fight for more compassionate approaches to drugs. “I think a lot of them have witnessed what happened to folks that are my age or younger, and I think it is a huge turnoff.” Mr. Sharp, who is 35, said he lost seven friends to overdose deaths in the past two years.

Just like youths in the crack era, however, this doesn’t mean young people aren’t doing other drugs. There’s a phenomenon known as generational forgetting, originally identified by Lloyd Johnston, who led the largest national survey on drug use among youths for the past 43 years. The idea is that young people often avoid the drug that is currently the most feared. But since they have little experience with those that were popular earlier, they are less aware of their potential dangers.

This results in a broadly defined cycle in which, roughly every 10 to 15 years, a different drug epidemic appears. Heroin, for example, was the demon drug of the 1970s, crack in the 1980s, heroin again in the 1990s, methamphetamine in the 2000s, prescription opioids in the 2010s and now fentanyl and other opioids that are being sold as heroin. By seeing and covering each crisis as being caused by a particular substance — without understanding why addiction persists — we miss the opportunity to use policy to reduce related harm.

A study published in the journal Science in 2018 found that rather than starting with the marketing of OxyContin in the late 1990s and early 2000s, the exponential rise in American overdose deaths actually began in 1979. Not coincidentally, economic inequality began to skyrocket at the same time. But in part because of racism and because the deaths involved different drugs and, for the most part, affected different groups of people in different regions — crack in cities and prescription opioids in rural areas — the rising trend was obscured. And politically, blaming drugs is easier than countering economic stresses.