The headlines have become grimly familiar: “More than 20 overdose deaths hit Middlesex in 3 weeks,’’ “Opioid overdoses kill 10 people in 12 days in Sacramento area,’’ “Opioid abuse has death grip on Tennessee.’’

But there’s a problem with this umbrella term “opioids.’’ It hides the fact that Americans are actually dying from two separate scourges: some are succumbing to heroin, others to prescription drugs like OxyContin, Percocet, and Vicodin.

Reacting to these very different epidemics with a set of policies focused on “opioids’’ may ultimately prove inadequate, even counterproductive. Because heroin and prescription opioids are killing different people, in different ways, across different parts of the country.

Heroin deaths are largely concentrated across New England and the Midwest, and heroin victims tend to be young men in their 20s and early 30s. By contrast, prescription opioids are killing people all across the country, especially people ages 45 to 54 and including a substantial number of women.

Perhaps most critical, a Globe anaylsis of death certificates compiled by the Centers for Disease Control and Prevention shows a marked shift toward heroin, which once contributed to less than 15 percent of opioid overdose deaths and now accounts for nearly 40 percent.

Reports from the front lines suggest that heroin overdoses may still be spreading. In the worst-case scenario, if the death rate in heroin-afflicted New England became a national norm, nationwide heroin deaths would double.

Two opioid epidemics

The last 15 years have seen a terrifying increase in the number of opioid deaths — counting both prescription drugs and heroin.

To understand this explosion in opioid abuse, it helps to break this story into two phases:

1999-2010

During this first phase, the overdose rate from prescription opioids increased by roughly 300 percent. That alarming growth was driven by newly popular prescription drugs like OxyContin, which flooded the market before spilling into the streets, where they found a ready market of users.

The impact was sudden and widespread, breaking across regional boundaries and claiming lives all across the country.

Throughout these years, heroin deaths remained muted. In 1999, there were about 0.7 heroin overdoses for every 100,000 people in the United States. In 2010, that numbers was 1.0, a slight increase but nothing to match the trauma of prescriptions drugs.

2010-2014

The years since 2010 have seen a tripling in heroin deaths, partly a result of growing popularity and partly from the deadly kick that comes from the widening practice of lacing heroin with Fentanyl.

And as heroin deaths have soared, prescription drug overdoses have largely plateaued, though an uptick in 2014 has raised concern of a comeback.

One key feature of the heroin surge is that it’s been fairly localized. Across New England and parts of the Midwest, heroin contributes to about half of all opioid-related deaths. In Connecticut, 59 percent of opioid-related deaths involve heroin. In Illinois, it’s 64 percent.

A slightly less-virulent heroin crisis is affecting the borderlands of the Southwest as well as the Pacific Northwest.

Yet, across the Great Plains and much of the Southeastern United States, heroin deaths remain far more rare. In Oklahoma and Kansas, Idaho and Wyoming, less than one in five opioid-related deaths stem from heroin.

The CDC cautions against putting too much weight on these state numbers, because some of the variations may stem from the fact that states report deaths in different ways. But the agency’s own research confirms the regional pattern, and detailed survey data from the Substance Abuse and Mental Health Services Administration tell a similar story.

Different drugs, victims

Heroin and prescription drugs aren’t just spreading through different regions; they’re also affecting different types of people, whether you look at age or gender.

Age

Prescription drug overdoses are most common among middle-aged Americans, 45 to 54, who account for about 25 percent of all prescription opioid deaths. When you add in 55- to 64-year-olds, you capture nearly half of all overdoses from prescription drugs.

With heroin, the situation is reversed. It’s the 25- to 34-year-olds who suffer most, with an overdose rate vastly higher than any other age cohort.

This complicates the familiar story of opioid abuse, where people get hooked on prescription drugs before shifting to heroin.

For young people, this may indeed be a real risk. One 2012 study suggested that 3 to 4 percent of opioid addicts do make the switch to heroin.

But this doesn’t seem to be happening among older Americans. For that age group, the prescription drugs themselves are the big risk.

Gender

Heroin chiefly afflicts men, but prescription drugs are a more equal-opportunity killer.

Nationwide, more than two of every five prescription opioid deaths involves women. In a few places, women are an outright majority of victims — including in Washington, Oregon, Nevada, and Idaho.

With heroin, nearly 80 percent of all deaths across the United States involve men.

A worrisome future

The fact that heroin deaths remain concentrated in a few geographic regions suggests a real risk of further spread. In fact, that spread may already be happening, hiding in plain sight simply because the death certificate data only extend through 2014.

One way to check is to talk to advocates, treatment experts, and public health officials working in places like Virginia, Iowa, and Minnesota — states that border heroin-plagued neighbors but where heroin wasn’t yet the dominant killer in 2014.

When you do, tales range from slight alarm to full-blown panic.

Kevin Gabbert, from the opioid treatment authority at the Iowa Department of Public Health, said that heroin deaths “may not be as significant as what you’re seeing in the eastern part of the country, but the rate of increase has been substantial,’’ adding that “in the course of five days in early April, there were five overdose deaths in the eastern part of the state, and heroin is among the drugs suspected to be involved.’’

More distressed was Carol Falkowski, once Minnesota’s drug abuse strategy officer and founder of the education group Drug Abuse Dialogues. “It’s just a matter of time until heroin overtakes prescription drugs in Minnesota,’’ she said. “Already, 16 percent of the people entering treatment in the Twin Cities are coming in for heroin, and it’s never been that high.’’

From Richmond, Honesty Liller painted a similar picture. Liller is chief executive of the McShin Foundation, which provides a host of addiction-recovery services, and when asked if the tide was turning toward heroin, she replied: “Heck yeah. Within the recovery community, we’ve seen a huge rise in heroin overdoses and deaths, particularly this year.’’

If these perspectives bear out, the 2015 and 2016 maps of heroin overdose deaths may include a lot more dark territory, fueling a further rise in the opioid death rate.

Two epidemics

Recognizing the current suffering and future risk, the federal government has been working with a variety of states to address the threat posed by opioid overdose in the United States.

Among the initiatives are increased funding for drug treatment programs, steps to block drug trafficking, and easier access to drugs that ease the path from heroin to sobriety.

But in this effort, there is no one-size-fits-all solution, and even well-meaning efforts can end up exacerbating the problem.

Here’s one example. In recent decades, virtually every state has passed laws to crack down on opioid prescriptions, shutting down “pill mills’’ and creating prescription monitoring programs to keep track of which doctors might be overprescribing.

More recently, the CDC has tightened its own guidelines to ensure these highly addictive drugs are only made available to patients who really need them.

But what if this crackdown on prescription opioids actually pushes more people toward heroin?

This may already be part of the reason young men have started dying from heroin in greater numbers. And if prescriptions get even harder to find, more women and older Americans may look to heroin as a way to soothe their pain, and their addiction.

This is the kind of risk that’s hard to foresee, unless you distinguish between America’s two crises, one involving heroin, the other prescription drugs.

Evan Horowitz digs through data to find information that illuminates the policy issues facing Massachusetts and the United States. He can be reached at evan.horowitz@ globe.com. Follow him on Twitter @GlobeHorowitz