UC San Diego Study: Overdose Deaths Drop 24% as Fourth Wave of Crisis Recedes for First Time

The United States overdose crisis has reached a pivotal inflection point. For the first time since the epidemic began escalating nearly three decades ago, mortality has declined across all four documented waves of the crisis simultaneously—a finding that represents both hard-won progress and a sobering reminder of how much work remains.

Research published June 2, 2026, in the journal Addiction by investigators at the University of California San Diego documents a 24.4% reduction in overdose death rates between 2023 and 2024. The national rate fell to 23.7 deaths per 100,000 people, down from a pandemic-era peak that claimed nearly 110,000 lives annually. Perhaps most significantly, deaths involving fentanyl combined with stimulants—what public health officials have termed the "fourth wave" of the crisis—declined for the first time since this particularly lethal pattern emerged.

"We are seeing a historic shift in the overdose crisis," said Joseph Friedman, MD, PhD, MPH, the study's first author and a resident physician in psychiatry at UC San Diego School of Medicine. "But this is not the end. The substances involved are changing, some parts of the crisis are still growing, presenting new challenges. We need to avoid interpreting declining national numbers as a sign that the crisis has been solved."

Mapping the Four Waves

The UC San Diego analysis, which examined every recorded overdose death in the United States from 1999 through 2024 using the CDC's WONDER database, traces the evolution of American addiction mortality through four distinct phases. The first wave began with prescription opioid analgesics in the late 1990s. Heroin surged as the second wave around 2010, followed by illicit fentanyl's catastrophic arrival as the third wave beginning in 2013. The fourth wave—fentanyl combined with stimulants such as methamphetamine and cocaine—emerged around 2018 and has proven especially deadly due to the pharmacological complexity of treating polysubstance overdoses.

The new data reveals that deaths involving fentanyl without stimulants fell from 31,193 in 2023 to 19,673 in 2024. Deaths involving fentanyl-stimulant combinations dropped from 41,583 to 28,062. These declines drove the overall mortality reduction and suggest that interventions targeting fentanyl exposure may finally be achieving population-level impact.

Multiple factors likely contribute to this turnaround. Expanded naloxone distribution has placed overdose reversal medication into the hands of more people who use drugs, their family members, and first responders. The elimination of the X-waiver requirement in 2023 removed a significant barrier to buprenorphine prescribing, allowing more primary care physicians to initiate medication-assisted treatment. Changes in drug use behaviors, including increased awareness of fentanyl's lethality, may have led some individuals to modify consumption patterns. Supply-side disruptions in illicit fentanyl distribution networks could also play a role, though researchers caution that such disruptions often prove temporary.

The Stimulant Warning

Beneath the encouraging headline numbers, the study reveals troubling countercurrents that threaten to reshape the crisis. Deaths involving stimulants without fentanyl continued their upward trajectory, rising from 18,142 in 2023 to 18,907 in 2024. These fatalities accounted for 17.3% of all overdose deaths in 2023 but grew to 23.8% in 2024—a proportion that continues expanding.

Xylazine, the veterinary sedative increasingly detected in the illicit drug supply, appeared in a growing share of fentanyl-related deaths and presents particular clinical challenges. Unlike opioid overdoses, xylazine toxicity does not respond to naloxone reversal, complicating emergency response protocols.

Senior author Steffanie Strathdee, PhD, professor of medicine at UC San Diego School of Medicine, emphasized that overdose mortality represents only one dimension of stimulant-related harm. "Stimulants are also associated with long-term cardiovascular, neurological and psychiatric harms that can devastate individuals and communities," she noted. "The health consequences extend far beyond acute overdose events."

Researchers warn that if current trends persist, stimulants may soon surpass opioids as the defining addiction-related public health challenge in the United States—a scenario that would require fundamentally different prevention and treatment approaches. Unlike opioid use disorder, which has multiple FDA-approved pharmacological treatments, stimulant use disorder lacks any medication with proven efficacy, leaving behavioral interventions as the primary therapeutic option.

Persistent Racial Disparities

The mortality decline has not been shared equally across demographic groups. Non-Hispanic Black individuals experienced the largest percentage reduction in overdose death rates, with a 29.3% decline between 2023 and 2024. However, this progress occurred from an elevated baseline—Black Americans' overdose death rate remained more than 1.5 times higher than the national average throughout 2024.

Non-Hispanic American Indian and Alaska Native populations faced the highest overdose death rate of any group studied, at 50.8 deaths per 100,000 people—more than double the national average. This disparity reflects longstanding inequities in healthcare access, economic opportunity, and historical trauma that continue to manifest in disproportionate addiction mortality.

The study also documented differential patterns in stimulant involvement. Cocaine-related deaths disproportionately affected Black Americans, while methamphetamine-related deaths disproportionately impacted American Indian and Alaska Native communities. Xylazine-related overdose deaths showed particularly elevated rates among Black Americans, suggesting that the evolving drug supply poses heightened risks for specific populations.

"National trends can improve while vulnerable communities continue to suffer disproportionately," Friedman observed. "The next phase of the response needs to focus not only on lowering overall deaths, but on making sure those gains reach the populations that have been hit hardest."

Global Context

Even with the documented decline, the United States remains a global outlier in overdose mortality. Approximately 80,000 people died from drug overdoses in the U.S. in 2024—a figure far exceeding what would be expected if American overdose death rates matched those of Western European nations. The gap reflects differences in drug policy, healthcare system structure, pharmaceutical regulation, and social safety net provisions.

The persistence of elevated mortality despite improvement underscores the structural nature of the American overdose crisis. While individual interventions—naloxone distribution, expanded treatment access, harm reduction services—have demonstrable impact, the underlying drivers of addiction vulnerability remain embedded in economic inequality, healthcare fragmentation, and the criminalization of drug use.

Implications for Policy and Practice

The UC San Diego findings carry significant implications for addiction treatment and public health policy. The simultaneous decline across all four waves suggests that comprehensive approaches addressing multiple intervention points can achieve measurable population-level outcomes. However, the continued rise in stimulant-only deaths and persistent racial disparities indicate that current strategies remain incomplete.

Treatment providers may need to prepare for a shifting clinical landscape. As stimulant use disorders become proportionally more prevalent, programs historically oriented toward opioid treatment will require enhanced capacity for managing cocaine and methamphetamine dependence. The absence of FDA-approved medications for stimulant use disorder places particular emphasis on behavioral interventions, contingency management, and psychosocial support—services that remain underfunded relative to medication-based opioid treatment.

Harm reduction strategies will similarly require adaptation. Xylazine's presence in the drug supply necessitates expanded wound care services, given the medication's association with severe necrotic tissue damage. Test strip distribution programs must evolve to detect emerging adulterants beyond fentanyl.

The study authors emphasize that sustaining progress will require continued investment in addiction treatment infrastructure, harm reduction programs, and targeted public health interventions addressing the communities experiencing the highest mortality burdens. The decline in overdose deaths, while welcome, represents the beginning of a longer trajectory rather than an endpoint.

"We have evidence that public health interventions can bend the mortality curve," Friedman concluded. "The question now is whether we have the political will and sustained commitment to ensure those benefits reach everyone who needs them."