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Junjie Gai_PhD Dissertation_05052.74 MB
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Dissertation
Essays on the impact of health policy on mental health and substance use disorder treatment
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2026
DOI: 10.25820/etd.008471
Abstract
Prescription drugs are powerful medical tools, but they drive two major crises in the United States: essential medications are often too expensive, while highly addictive drugs have fueled an ongoing overdose epidemic. My research explores how government policies attempt to solve these twin challenges. This dissertation aims to investigate the impact of health policy on the mental health and substance use disorder treatment, especially for opioid use disorder.
Using Medical Expenditure Panel Survey data from 2006 to 2019, my first study assessed the effect of closing Medicare Part D coverage gap on mental health of older adults. This study employed difference-in-differences and compared mental health outcomes of older adults on Medicare with those on private insurance before and after the 2011 policy change. Findings showed a 0.447-point reduction in the Kessler Index 6 score after closure. This indicates that the policy successfully reduced psychological distress. By eliminating the prohibitive out-of-pocket costs in the coverage gap, Medicare beneficiaries likely experienced less financial anxiety and better medication adherence, leading to tangible improvements in their mental health. These findings were mainly attributable to women, Hispanics, individuals with multiple chronic conditions, and those in Traditional Medicare. A reduction in out-of-pocket expenditures appeared to be the primary mechanism for this finding. Our analysis was robust to several specifications, including using different measures of mental health and alternate constructions of treatment and control groups. The closure of the Medicare Part D coverage gap improved mental health among beneficiaries, potentially by reducing financial strain associated with high out-of-pocket expenditures.
Second. Medicare beneficiaries with opioid use disorder (OUD) face challenges in accessing Medication Assisted Treatment (MAT), which combines pharmacotherapy with counseling and behavioral interventions. Before 2020, Medicare Part B did not reimburse MAT services delivered in specialized outpatient clinics known as Opioid Treatment Programs (OTPs). The Substance Use Disorder Prevention that Promotes Opioid Recovery and Treatment for Patients and Communities (SUPPORT) Act expanded Medicare Part B coverage to OTPs beginning January 1, 2020. This coverage included reimbursements for medications (particularly Methadone), outpatient services, counseling, and toxicology testing for OUD treatment provided at OTPs. This study examines whether expanded coverage influenced OUD treatment patterns (including type of treatment utilized and treatment completion) by comparing Medicare beneficiaries with OUD to those with other substance use disorders. Using the Treatment Episode Data Set (2015-2023) and a difference‑in‑differences approach, we assessed changes in receipt of different services (outpatient, inpatient, detoxification services) and probability of treatment completion. After the policy took effect, Medicare beneficiaries with OUD were more likely to receive non‑intensive outpatient services. However, the probability of treatment completion for non-intensive outpatient treatment decreased as a consequence of the policy. The decline in program completion signals an important unintended consequence, raising concerns for long-term recovery and emphasizing the complementary need for improved care coordination and patient and provider education.
The third study shifts to the intersection of criminal justice and public health by evaluating the downstream clinical impact of state Good Samaritan Laws (GSLs) on OUD treatment. While GSLs were designed to reduce immediate overdose mortality by providing statutory immunity to bystanders, this study provides the first causal evidence that these legal protections successfully translate into increased utilization of formal OUD treatment. Using a staggered Callaway Sant’ana Difference-in-Differences (CSDID) design and TEDS-A data from 2006 and 2019, the analysis reveals that GSL enactment significantly increased admissions for Medications for Opioid Use Disorder (MOUD) and acute detoxification. This increase is driven primarily by self-referred individuals overcoming legal-induced self-stigma, and healthcare providers leveraging acute emergency encounters, though significant racial and demographic disparities in downstream treatment assignment persist.
Collectively, these three studies demonstrate that improving health outcomes and treatments requires a multi-faceted policy approach. While federal insurance expansions are critical for reducing financial distress and building outpatient capacity, dismantling the structural threat of criminalization is a necessary prerequisite to moving high-risk individuals out from the shadows and into the healthcare continuum.
Details
- Title: Subtitle
- Essays on the impact of health policy on mental health and substance use disorder treatment
- Creators
- Junjie Gai
- Contributors
- Kanika Arora (Advisor)Ryan Carnahan (Committee Member)Dan Shane (Committee Member)Hari Sharma (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Health Services and Policy
- Date degree season
- Spring 2026
- DOI
- 10.25820/etd.008471
- Publisher
- University of Iowa
- Number of pages
- xii, 124 pages
- Copyright
- Copyright 2026 Junjie Gai
- Language
- English
- Date submitted
- 04/27/2026
- Description illustrations
- Tables, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 83-98).
- Public Abstract (ETD)
Prescription drugs are powerful medical tools, but they drive two major crises in the United States: essential medications are often too expensive, while highly addictive drugs have fueled an ongoing overdose epidemic. My research explores how health policies attempt to solve these twin challenges.
This dissertation evaluates three major policy changes. First, it examines how the Affordable Care Act and Medicare Part D lowered costs to make medications more accessible and mental health more improved by relieved financial stress. Second, it looks at how the federal SUPPORT Act expanded the healthcare system's capacity to treat opioid addiction among Medicare beneficiaries with opioid use disorder. Finally, it investigates state Good Samaritan Laws, which protect people from arrest when they call 911 for an overdose. The findings show that while these policies successfully remove financial and legal barriers, patients still experience fragmented care.
To sum up, this research shows that changing health policy is only the first step. To solve these public health crises, we need to dismantle the biases within our healthcare facilities so that every patient receives fair and life-saving care.
- Academic Unit
- Health Management and Policy
- Record Identifier
- 9985176872702771
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