Overdose deaths and fentanyl use have declined nationally, representing a rare glimmer of hope for the substance use disorder (SUD) treatment industry.
However, new research shows that people are increasingly using heroin and methamphetamine, suggesting potentially dangerous broader reasons for the decline in fentanyl use.
Heroin use among fentanyl users increased by 18% nationwide from 2023 to 2024, according to the annual Signals Report from Millennium Health. This uptick in heroin use occurred suddenly and dramatically, according to Eric Dawson, vice president of clinical affairs for Millennium Health.
“Last July, I would have said, we almost see no heroin in urine specimens in that population using fentanyl. It’s almost exclusively fentanyl,” Dawson told Addiction Treatment Business. “In September, I would have said we have seen a resurgence of heroin use among this population using fentanyl. That’s how quickly it happened, literally in August to September, we saw this surge in heroin detection among those using fentanyl, especially out West.”
San Diego, California-based Millennium Health is one of the largest urine drug testing laboratories in the U.S. and monitors drug use trends. The organization found that the number of urine tests showing positive for fentanyl fell more than 12% since its peak in 2022.
The report, which analyzed data from over 1.4 million urine drug tests, found that polysubstance use continues broadly across illicit drug users. Approximately 93% of fentanyl users also used other drugs, with over 29% testing positive for four or more additional drugs. These findings mark a “polysubstance use crisis,” Dawson said.
Geographical differences
Drug use varied geographically. Methamphetamine was most commonly used alongside fentanyl in the western U.S., with over 78% of fentanyl users also using the stimulant. No FDA-approved drugs exist for stimulant disorders, making the trend especially dangerous.
Cocaine was more commonly used along with fentanyl in the Northeast, with 54% of fentanyl users also turning to the drug. Heroin co-use increased generally across all regions, but most dramatically in the Midwest and South.
Increases in heroin use may be due to disruptions in the fentanyl trade, according to Dawson.
“We believe it to be a supply-sided phenomenon,” he said. “We say that because this increase in heroin that we saw, both in terms of the timing and the extent of the increase, was very consistent across most of the western states. So we believe it was an intentional act by drug trafficking organizations, likely in response to some disruption in the fentanyl supply, that they turned to heroin as an alternative.”
Patients are turning to fentanyl alternatives
Heroin has similar, though less potent, effects than fentanyl, making it an ideal candidate as a substitution.
In the near term, this trend may lead to a further reduction in overdose numbers, Dawson said. However, if the disruption in the fentanyl supply chain ends, or if the heroin supply becomes limited, drug trafficking organizations may turn to even more dangerous agents like carfentanil.
Carfentanil, a synthetic opioid 100 times more potent than fentanyl, was detected in 0.5% of fentanyl users in 2024, a 350% increase since 2023. Increased carfentanil use could be “devastating” for rates of overdose deaths, Dawson said.
Xylazine, a veterinary tranquilizer with effects similar to fentanyl, also increased. Over 21% of fentanyl users also used xylazine in 2024, a 19% increase since 2023.
“If there is then a move from heroin to some other drug that is much more potent, than these gains that we’ve seen in terms of fentanyl overdoses, the falling numbers could be quickly reversed,” Dawson said. “This heroin story as we move into 2025 is one that we’re watching very closely.”
Given that no FDA-approved treatment exists for acute intoxication or stimulant use disorders, providers should share their best practices for treating polysubstance use, Dawson said.
