Last year I noted the disconnect between rising public alarm about methamphetamine and falling rates of use. By 2005, when Newsweek identified "The Meth Epidemic" as "America's New Drug Crisis" in a sensational cover story, illicit methamphetamine use had been declining for years. A new report on data from the government-sponsored Monitoring the Future (MTF) Study, which surveys eighth-graders, 10th-graders, 12th-graders, college students, and young adults, makes a similar point:

Methamphetamine questions were introduced in 1999 because of rising concern about use of this drug; but a decline in use has been observed among all five populations in the years since then, through about 2012. In 2014 annual use in all five populations was very low—particularly among college students (0.1%). These substantial declines occurred during a period in which there were many stories in the media suggesting that methamphetamine use was a growing problem—an example of the importance of having accurate epidemiological data available against which to test conventional wisdom.

That is not the only way in which MTF data contradict, or at least complicate, the warnings of drug warriors and their flacks in the press. Here are a few more examples that struck me while reading the report.

Bath Salt Blowout

A few years ago, MTF started asking about the synthetic cathinones sold as "bath salts," which supposedly were catching on all over the country, driving users to mutilate themselves, commit suicide, and eat the faces of innocent bystanders. Since the question about "bath salts" was added in 2012, use rates have been "very low" and mostly declining. Between 2012 and 2014, the rate of past-year use fell from 0.8 percent to 0.5 percent among eighth-graders, from 1.3 percent to 0.9 percent among 12th-graders, from 0.3 percent to 0.2 percent among college students, and from 0.5 percent to 0.4 percent among young adults (ages 19 to 28). Past-year use rose slightly among 10th-graders between 2012 and 2014, from 0.6 percent 0.9 percent, a difference that was not statistically significant.

Salvia Slide

Six years ago in Reason, I described the proliferation of state bans on Salvia divinorum, a psychedelic herb that had somehow escaped prohibitionists' attention since the 1930s, when Western anthropologists started describing its ritual use in Mexico, which goes back hundreds of years. Alarmed by their discovery of a psychoactive plant whose existence they had unknowingly tolerated, state legislators rushed to correct their oversight, fearful that it "could become the next marijuana," as the Associated Press put it.

Salvia did not quite take off the way the alarmists predicted. In 2009, when MTF first asked about the drug, 3.5 percent of young adults reported using it in the previous year. Last year the rate was 1.2 percent. Similarly, past-year salvia use by 12th-graders fell from 5.7 percent in 2009 to 1.8 percent in 2014. By comparison, 32 percent of young adults and 35 percent of high school seniors used marijuana that year.

Something About Molly

MDMA, a.k.a. Ecstasy or (more recently) Molly, is considerably more popular than salvia. According to the MTF data, it was used by 3.6 percent of 12th-graders, 5 percent of college students, and 4.8 percent of young adults last year. But those rates are much lower than the peaks seen in 2001, when 9.2 percent of both 12th-graders and college students, along with 7.5 percent of young adults, admitted using MDMA.

It looks like peak MDMA use came a few years before peak MDMA hysteria, as embodied in Joe Biden's Illicit Drug Anti-Proliferation Act of 2003, which targeted raves and other events where use of the drug was common. By the time Biden's bill passed, past-year use by 12th-graders and college students had fallen from peak levels by more than 50 percent, while past-year use by young adults had fallen by 40 percent.

Heroin Hype

Public alarm about heroin also seems only loosely related to trends in use. Contrary to the impression you might get from all the talk of a "heroin epidemic," MTF data indicate that use of the drug by young people has not risen in recent years.

After falling by 50 percent between 1975 and 1979, the prevalence of past-year heroin use among 12th-graders remained stable at 0.5 percent or so until 1995, when it doubled. The rate peaked at 1.5 percent in 2000. Last year it was 0.6 percent.

Trends were similar for the other age groups. "After the period 1999 to 2001," says the MTF report, "heroin use fell back to lower levels than were observed in the mid- to late-1990s….All age groups except for the young adults had annual levels of heroin use in 2014 that were well below recent peaks (by roughly one half to two thirds). Young adults have remained at peak levels (0.4–0.6% in 2008–2014)."

Recent data from the National Survey on Drug Use and Health (NSDUH), which covers Americans 12 and older, show a gradual increase in the number of past-year heroin users, from 373,000 in 2007 to 681,000 in 2013. "Heroin use remains uncommon in the United States," says the NSDUH report, although "the percentage of people using heroin is higher in 2013 than it was a decade ago." Data for last year are not available yet.

By contrast, public concern about a "heroin epidemic," as measured by the use of that phrase in newspaper and wire service articles collected by Nexis, has risen precipitously. Between 2011 and 2013, when the number of past-year users indicated by NSDUH data rose by about 10 percent, the number of "heroin epidemic" mentions rose by almost 700 percent, from 82 to 633. Last year press references to a "heroin epidemic" skyrocketed to more than 3,000, driven largely by a single event: the heroin-related death of actor Philip Seymour Hoffman.

MTF and NSDUH probably miss a substantial number of heavy users, and the number of overdose deaths involving heroin did rise from 4,397 in 2011 to 8,257 in 2013. But even that increase pales beside the explosion in press coverage.

Data Delay

As these examples (and others) suggest, the relationship between reality and public pronouncements about drugs can be tenuous. Supposedly scary new intoxicants may never attract much of a following, while the ebb and flow in use of more familiar substances may correspond only roughly, if at all, to the level of political panic about them. The problem is that data showing the fizzling of fads or putting into perspective the drug scare du jour usually are not available in the heat of the moment, when policy tends to be made.

This article originally appeared at Forbes.com.