Who should carry the drug?

“Active drug users, people who live with or love drug users, and people on methadone or buprenorphine, who are often coming out of treatment and know people at high risk of overdose,” said Robert Childs, executive director of the North Carolina Harm Reduction Coalition in Wilmington, N.C. The surgeon general also listed patients who take high doses of prescribed opioids.

People who are coming out of prison or detox programs should carry the drug, because detox lowers tolerance, Mr. Childs said. Those who work in places where there are public bathrooms or where drug users congregate, such as shopping center parking lots, should consider getting trained to use naloxone and keep it on hand.

“It should be just like carrying a first aid kit,” Mr. Childs said.

How do you know if someone is overdosing?

If someone has shortness of breath or is not breathing, is unresponsive or won’t wake up and has pale or discolored skin, they may be overdosing. Other signs include pinpoint pupils, confusion, vomiting and cold or clammy skin.

Trainers will frequently instruct people to perform what is known as a sternum rub.

“You make a fist and with your knuckles you go up and down the sternum as hard as you can,” said Mr. Childs. “It causes excruciating pain, so if someone does not respond to that, you know they are in a state worth responding to immediately.”

If someone is awake, look at their eyes. “Mostly you see the iris, just a tiny black spot in the middle,” said Dr. Steven Daviss, senior medical adviser at the Substance Abuse and Mental Health Services Administration, which is part of the Department of Health and Human Services. “That’s a pretty good sign someone has overdosed on an opioid.”