The decrease across the country is a major breakthrough in efforts to reverse the effects of fentanyl. Researchers and health officials say there is no easy explanation for the trend.

For years, drug overdose deaths in the U.S. had been on the rise. This year, data indicates they’ve suddenly started to decline. The reason behind the drop is a mystery.

In this Jan. 25, 2024, file photo, a used Narcan brand Naloxone nasal spray rests on the street after paramedics and police responded to a suspected fentanyl drug overdose in Portland, Oregon. — Patrick T.