This first decline in five years is "encouraging news for our nation and shows that we are making progress," said Deb Houry, chief medical officer for the Centers for Disease Control and Prevention (CDC).

But the data "does not mean that we have turned the corner," she added.

The trend "should give us encouragement to intensify our efforts, knowing that our strategies are working," she said.

The United States recorded about 107,000 overdose deaths last year, down from more than 111,000 in 2022, a 3 percent decrease, according to provisional figures released by US health authorities.

The main culprit in America's ongoing overdose crisis is fentanyl, an extremely potent and addictive synthetic opioid that began flooding the drug supply about a decade ago.

Deaths involving fentanyl fell to just under 75,000 last year, from more than 76,000 in 2022.

"Many factors are likely playing a role" in the decline, Joseph Friedman, a researcher specializing in the issue at the University of California, Los Angeles, told AFP.

Among them are "increased access to addiction treatment" and "increased access to naloxone," an overdose-reversal medication, he said.

Another possible explanation is that "fentanyl has spread," and has now "saturated all the new places it can go," he added.

However, overdose deaths involving cocaine or stimulants like methamphetamine increased, according to the CDC data.

There were also stark regional disparities, with overdose deaths falling by 15 percent or more in Nebraska, Kansas and Maine, but rising by 27 percent or more in Washington, Alaska and Oregon, all in the western part of the country.

"While the apparent stabilization in overdose deaths compared to prior years' increases is encouraging, there is no indication that the fundamental structural factors driving this crisis have meaningfully changed," Friedman warned.

"Continued efforts are needed to encourage people who use fentanyl to stabilize on safer opioids such as methadone or buprenorphine," which are available by prescription, he said.

In the spring of 2023, the US Food and Drug Administration (FDA) authorized for the first time the over-the-counter sale of naloxone in the form of a nasal spray known by the brand name Narcan.

The US opioid crisis began in the 1990s with the overprescription of prescription opioids, which were pushed to the public by the healthcare system, especially for pain management.

When the US began cracking down on access, some people turned to heroin, leading to a spike in overdose deaths involving the drug starting in 2010.

The third wave began in 2013, with a surge in deaths involving synthetic opioids, including fentanyl.

Now, fentanyl is increasingly being "mixed with stimulants," according to Friedman, who believes this trend marks the beginning of a fourth wave.

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