Demand is booming.
For decades, naloxone, a drug approved in 1971 that instantly reverses the effect of opioid overdose, languished in relative obscurity. Outside of emergency rooms and outreach programs in high-risk communities, few saw the public-health potential. Many even argued that it encouraged substance abuse.
Not anymore. Today school nurses, police officers, and firefighters increasingly carry naloxone. New laws in 37 states allow friends and family members of opioid users to obtain a prescription. The FDA has called for more user-friendly forms of the drug—it approved a nasal-spray version in November. And 29 states have issued standing orders that effectively make it available over the counter.
The increased adoption is driven, of course, by the nation’s deepening opioid epidemic—a scourge fueled by prescription pain pill abuse and cheap heroin that resulted in 24,200 overdose deaths in 2013, up 315% from 1999. Estimates put the cost of the epidemic at $55 billion to $72 billion a year.
Naloxone’s rise to prominence has been good for its manufacturers, Amphastar Pharmaceuticals and Pfizer PFE , which both doubled the price over the past two years. (Three other companies, Mylan MYL , Kaléo, and Adapt Pharma, also recently entered the market.) But more significant: It saved 8,000 people from an overdose last year—a number that’s growing fast.
A version of this article appears in the December 15, 2015 issue of Fortune.