After years of relentless rises in overdose deaths, the United States has seen a remarkable reversal. For seven straight months, according to federal data, drug fatalities have been declining.

Expanded treatment, prevention and education efforts are playing a role, but drug policy experts believe there is another, surprising reason: changes in the drug supply itself, which are, in turn, influencing how people are using drugs.

The fentanyl on the street is starting to become weaker. Anne Milgram, who heads the Drug Enforcement Administration, announced last week that for the first time since 2021, the agency was seeing a decline in fentanyl potency, a development she attributed to the government’s crackdown on Mexican cartels and international supply chains. Last year, seven out of 10 counterfeit pills tested in D.E.A. labs contained a life-threatening amount of fentanyl, she said, but that number has dropped to five out of 10.

Addiction experts say that other interventions contributed to the declining fatalities, including wider distribution of overdose reversal medications like Narcan; an uptick in some states in prescriptions for medication that suppresses opioid cravings; and campaigns warning the public about fentanyl-tainted counterfeit pills.

Harm reduction programs that offer sterile syringe exchanges and fentanyl test strips are also saving lives, experts note. Many treatment and support services that were shuttered during the coronavirus pandemic have become more accessible.

“They are all part of a health response to substance use that is bending the curve,” said Dr. Brian Hurley, the president of the American Society of Addiction Medicine.