The training session began just after 8 p.m. in an empty high school science classroom.

Amid the microscopes and anatomy charts, Roselyn Heath wore the weary look of a worried mother. Her 21-year-old daughter had tried repeatedly to kick her OxyContin addiction but, once again, was showing signs of relapse. Heath wondered how to spot the signs if her daughter overdosed.

“How would you know?” she asked.

The first sign is unresponsiveness, said Peggy Sarmento, herself the parent of a recovering heroin addict. “Their lips are blue; their fingernails are blue,” she said. “They’ll do what we call a ‘death rattle.’ ”

From a small bag, Sarmento pulled a vial of medication, a plastic canister and a foam tip that turns liquid into a nasal spray. She showed Heath how to assemble them into a dose of naloxone — an antidote that can rapidly reverse an overdose caused by opiate drugs such as oxycodone, hydrocodone and heroin. Keep it close by, she told Heath, handing her a kit with two doses. Just in case.

Overdose prevention kits include naloxone, a heroin antidote administered through the nose that can reverse the effects of an opioid overdose. (Andrew Burton/Getty Images)

“No one ever overdoses on purpose,” Sarmento said.

The training took barely 15 minutes, but it offered a glimpse into the growing effort to get naloxone, commonly known by the brand name Narcan, into the hands of more people on the front lines of the nation’s unrelenting opioid epidemic. Until the past few years, naloxone has been used mostly by paramedics, hospitals and drug-treatment programs.

But as opioid deaths surge — an estimated 16,000 lives are lost to overdoses each year — government officials, nonprofit groups and community activists are pressing hard to get naloxone into the hands of police officers, firefighters and especially addicts’ family members and friends.

Opioid overdoses are marked by depressed breathing, extreme fatigue and changes­ in heart rate. Victims tend to lose consciousness and deteriorate rapidly. Naloxone temporarily counteracts those effects by blocking opiate receptors in the brain, allowing normal respiration to resume and buying time to get the patient medical treatment.

In Tewksbury and nearly a dozen other Massachusetts towns, relatives come each week for free training on how to administer the antidote by Learn to Cope, a support group for family members with loved ones addicted to heroin, OxyContin and other opiates. They leave with kits — the group hands out more than 500 a month under a physician’s “standing order” — along with the peace of mind that if an overdose were to occur at home, having naloxone could mean a second chance instead of a funeral.

Efforts like the one in Tewksbury are unfolding across the country. For example, nearly two dozens states and the District have enacted legislation making it easier for opioid users’ friends and family to get the antidote.

Community-based naloxone distribution programs have existed in the United States since 1996, providing the drug to more than 50,000 people and reversing more than 10,000 overdoses, according to the Centers for Disease Control and Prevention. But for years, those groups operated without much support from governments or society.

“The impact it had on people was very obvious to anyone who would look. It’s just that some people weren’t willing to look,” said Dan Bigg, director of the Chicago Recovery Alliance, one of the nation’s oldest and largest naloxone distribution programs, which began in 1996.

But as prescription painkiller deaths skyrocketed through the 2000s and heroin abuse became a suburban as well as an urban scourge, more people began to acknowledge the value of naloxone — not as a cure, but as a vital tool in preventing deaths, Bigg said.

When Massachusetts Gov. Deval L. Patrick (D) declared a public health emergency in March because of soaring opiate abuse, he directed the state’s health department to make naloxone available immediately to all police, firefighters and other first responders, and to make it more accessible to the families and friends of drug abusers. In April, New York Attorney General Eric T. Schneiderman announced a $5 million effort to equip the state’s law enforcement officers with naloxone, saying that doing so “will save countless lives.” The program will be funded in part by money seized from drug dealers.

Last month, New York City’s police force, the nation’s largest, announced that it would use some of that money to equip about 20,000 of its officers with naloxone. While some law enforcement officials have expressed unease about asking police officers to take on a medical role and the possible liability issues that could result, departments across the country, including in Maryland, New Jersey and Wisconsin, are moving to train and equip first responders with naloxone.

Many of those efforts follow a model set by police in Quincy, Mass., who have reversed more than 250 overdoses since officers began carrying naloxone in 2010 and have won praise from the White House for their efforts.

Federal officials also have begun to embrace wider distribution of naloxone as one tool in trying to stem the body count from overdoses.

“It’s a really miraculous drug in terms of its ability to save lives,” Michael Botticelli, acting director of the Office of National Drug Control Policy, told lawmakers in March, adding that his office was working with federal, state and local officials to put more naloxone distribution programs in place. In April, U.S. Attorney General Eric H. Holder Jr. called on all of the nation’s first responders, state and local, to get trained in the use of naloxone.

Not everyone has embraced the idea of expanded access to naloxone. Last year, Maine Gov. Paul LePage (R) vetoed a bill to expand the availability to police and firefighters, as well as to family members of addicts, arguing that having easy access to an inexpensive antidote could give addicts “a false sense of security” and actually encourage drug use. (Maine’s legislature unanimously passed a similar bill this spring, which LePage allowed to become law without his signature.)

Advocates of naloxone say that there is little evidence to support those fears and that such a stance misunderstands the very nature of addiction.

“As a parent, you just want to have everything in your arsenal that you can get to save your child,” said Brigitte van Essen of Foxborough, Mass., who in 2011 used Narcan to reverse a heroin overdose by her son, who got treatment and now works as a mechanic. “If there’s no overdose reversal, there’s no second chance.”

As the use of naloxone expands, even the way the antidote gets administered is evolving.

Naloxone, which isn’t addictive and has no side effects, has long been given through a standard injection or a nasal spray. But in April, the Food and Drug Administration approved a new device aimed at making it easier to administer the antidote without training. The product, called Evzio, is about the size of a credit card and is designed to work much like the EpiPen, which is used to treat life-threatening allergic reactions. When activated, it can give verbal instructions to the user. The device is due to hit the market in July, and while its manufacturer hasn’t disclosed the price, it probably will be much more expensive than existing naloxone products.

Federal officials fast-tracked Evzio’s approval, with FDA Commissioner Margaret A. Hamburg calling it “an extremely important innovation.” The agency has yet to decide whether naloxone should be sold over the counter.

Kaleo, the Richmond-based company behind Evzio, envisions a time when its naloxone device will be prescribed alongside prescriptions for any opioid drug and “in every medicine cabinet of every person who might be at risk,” said Eric Edwards, the company’s co-founder and chief medical officer. Noting that many people who accidentally overdose on opioids are chronic-pain patients who have been prescribed the drugs, Edwards said, “We want it to go wherever opioids are present.”

On a recent night in Tewksbury, at the weekly support group for parents and siblings of people with heroin and prescription drug addictions, the dozens of regulars sat in a large circle, sipped Dunkin’ Donuts coffee and shared stories of jail stints and treatment centers and relapse. They urged Heath, who had come for her first meeting that night, not to go home without naloxone.

“There were times when I would wonder if she was going to wake up after she went to bed,” said Heath, who asked to be identified by her maiden name to protect her daughter’s privacy. “There were times that I would go in there and check to see if she was breathing.” And then, “I just really — I never thought I would have a kid on drugs.”

After the training, Sarmento scribbled her cellphone number on a piece of paper and urged Heath to call if she ever needed to talk. Heath thanked her, tucked the naloxone kit into her purse and drove home through a steady New England rain. She put the antidote in her nightstand, hoping its presence might help her sleep a little better, hoping she would never need to use it.