Oakland, CA – Independent Medical Reviews (IMRs) used to resolve California workers’ compensation medical disputes are now trending up after hitting a record low during the pandemic according to a California Workers’ Compensation Institute (CWCI) analysis of 1.68 million IMR decision letters issued from 2015 through 2025.

IMR was established under the state’s 2012 workers’ comp reform law (SB 863) to resolve disputes over medical treatment requests that are modified or denied through Utilization Review (UR). When a treating physician’s request for treatment is modified or denied by a UR physician, injured workers may dispute the decision and ask to have an independent physician evaluate the request using evidence-based standards from California’s Medical Treatment Utilization Schedule (MTUS) or other applicable guidelines for their injury. With revised regulations governing UR, IMR, and physician reporting aimed at reducing IMR delays, expediting injured workers’ access to care and prescription drugs, and increasing claims administrator and UR vendor accountability set to take effect April 1, the CWCI analysis provides benchmark data on how the medical dispute resolution process has been operating.

To track IMR volume, CWCI tallied the number of IMR decision letters issued during the 11-year study period by Maximus, which administers the program for the state. The data show the letter count rose from 165,525 in 2015 to 184,735 in 2018, then declined for four years, falling to 127,215 in 2022. That decline coincided with several developments—including the adoption of Opioid and Chronic Pain Guidelines in 2017 and implementation of the MTUS Prescription Drug Formulary in 2018—which sharply reduced prescription drug disputes that had accounted for nearly half of all IMRs. The pandemic also contributed to the decline as claim volume temporarily dropped and many COVID-19 claims filed between 2020 and 2022 required little or no treatment. Since then, however, IMR volume has rebounded, as the number of decision letters increased 2.9% in 2023, 8.2% in 2024, and 7.6% in 2025.

Prescription drugs still represent more IMR disputes than any other medical service category, but their share of the IMRs fell from 50.7% in 2015 to 30.5% in 2025 while other categories saw their share grow. These include physical therapy (which went from 8.3% of the IMRs to 14.0%), injections (which went from 6.9% to 12.8%), and durable medical equipment, prosthetics, orthotics and supplies (which went from 7.3% to 9.4%). Smaller increases were also noted for acupuncture and chiropractic manipulation. These trends suggest that as the pharmaceutical disputes declined IMR activity largely shifted toward physical medicine and alternative pain management services.

Despite the fluctuations in IMR volume and the shifts in the mix of disputed services, IMR outcomes have remained highly consistent. From 2015 through 2025, IMR physicians upheld UR physicians’ decisions between 88% and 92% of the time, including 89.8% in 2025, indicating strong alignment between the UR decisions and evidence-based medicine recommendations. As in the past, uphold rates varied by service category in 2025, ranging from 79.9% for evaluation and management services—primarily consultation requests—to 93.9% for acupuncture. Among prescription drug IMRs, the uphold rate was 91.2%, including 95.3% for opioids, 97.7% for hypnotic drugs, and 98.6% for musculoskeletal drugs, reflecting continued adherence to the Formulary and the MTUS Guidelines.

The study also found that IMR activity remains highly concentrated among a small group of physicians. Of the 8,140 providers identified in the 2025 IMR letters, the top 1% (81 physicians) accounted for 42% of the disputed treatment requests, while the top 10 physicians accounted for 11%. Six of the top 10 were pain management specialists and two were physical medicine and rehabilitation specialists. Four of the five highest-volume requesting physicians practiced in the Bay Area, which generated a disproportionate share of IMR disputes. While the region accounted for 15.7% of all California workers’ compensation claims in 2025, it generated 22.9% of IMR disputes, underscoring the influence of local practice patterns and high-volume providers on IMR volume.

Overall, the findings indicate that IMR continues to function as intended—reinforcing evidence-based medical decision-making and validating UR determinations in the vast majority of cases. At the same time, the rebound in IMR submissions despite relatively stable claim counts may prompt additional policy discussions focused on improving system efficiency, particularly in areas such as treatment modifications—which accounted for roughly one out of every eight IMRs last year—and the role of high-volume providers in driving dispute activity.

CWCI’s analysis has been published in a Research Update Report “Independent Medical Review Trends and Outcomes: 2015–2025.” Complimentary copies of the report are available by emailing requests to pmedrano@cwci.org. CWCI members may also request the latest set of IMR slides updated with data through 2025. The revised UR, IMR and physician reporting regulations are available here.