New drug testing data reveal that fentanyl concentrations across the western United States have climbed to their highest levels on record, a trend researchers say could be fuelling a fresh rise in overdose deaths.

The findings come from Millennium Health’s latest Signals Report, published in July 2026, which examined more than 976,000 clinical urine drug test results collected between January 2024 and June 2026. Researchers tracked changes in fentanyl detection rates, normalised fentanyl concentrations, and the presence of heroin and xylazine among people who tested positive for fentanyl.

A supply shock, then a rebound

The story begins in 2023, when overdose deaths started falling sharply nationwide. A separate study found this decline lined up with an approximate 50 per cent drop in illicit fentanyl purity, based on National Forensic Laboratory Information System data. Around the same time, social media posts describing a perceived “fentanyl drought” became more common, adding weight to the idea that a disruption in the fentanyl supply, rather than a change in demand, was behind the falling death toll.

Millennium Health’s urine testing data appeared to back this up. Between June and September 2024, as fentanyl concentrations dropped by as much as 58 per cent in the west compared with January 2024 levels, detections of heroin and xylazine both spiked, rising by 175 per cent and 129 per cent respectively. Researchers suggest people using fentanyl may have turned to these substances to cushion a temporary shortfall.

That picture began to shift from October 2024. Fentanyl concentrations in the western region rebounded quickly, increasing by 347 per cent between September 2024 and April 2025, while heroin and xylazine detections fell back just as sharply. The rebound in fentanyl potency coincided with overdose deaths reversing course in the west, even as they slowed across the eastern half of the country over the same period.

Fentanyl strength climbs again

After a period of relative calm through much of 2025, the report found that fentanyl concentrations in the west began climbing once more from November 2025, eventually reaching an all time high in May 2026, up 134 per cent on January 2024 levels. Notably, heroin and xylazine detection rates fell to their lowest points since January 2024 during this same window, a pattern researchers say is consistent with a genuine increase in fentanyl strength rather than a shift towards substitute drugs.

Regional mortality figures included in the report show just how closely these shifts in fentanyl concentrations have tracked overdose deaths. By November 2025, the fentanyl involved overdose death rate stood at 12.0 per 100,000 people in the west, compared with 9.6 in the northeast, 7.3 in the south and 6.4 in the midwest, the lowest of the four regions.

A different story in the east

The pattern looked markedly different across the rest of the country. In the eastern regions, fentanyl concentrations also fell during 2024, by around 41 per cent, while increases in heroin and xylazine use were far less pronounced, rising by 29 per cent and 30 per cent respectively. Rather than rebounding, fentanyl concentrations in the east continued to soften, dropping a further 48 per cent into early 2025 and remaining below January 2024 levels right through to mid 2026, even as they ticked up slightly towards the end of the study period. Overdose death rates in the eastern regions have flattened as a result, rather than climbing as they have further west.

Why it matters

Millennium Health’s researchers argue the findings show how closely fluctuations in fentanyl concentrations can foreshadow shifts in overdose mortality, often months before official death figures catch up. With fentanyl potency once again climbing sharply in the west, and overdose deaths reportedly rising through the first half of 2026, the report’s authors say ongoing monitoring of drug testing data offers a rare, real time window into a rapidly shifting and unpredictable drug supply, one that continues to leave communities across the country exposed to serious harm.

Source: thedrugreport