Mobile App Cuts Substance Use by Half Among Unhoused Populations, WashU Study Finds

When Dr. Vidya Eswaran sees patients in the Barnes-Jewish Hospital emergency department, she encounters a stark reality: people struggling with housing insecurity face distinct barriers to substance use treatment that traditional interventions often fail to address. Inconsistent access to care, heavier mental health burdens, and the daily challenge of survival leave little room for conventional treatment schedules.

A new study from Washington University School of Medicine suggests a different approach might work—one that fits in a pocket.

Housing Insecurity Meets Digital Health

Research published February 1 in Drug and Alcohol Dependence examined the uMAT-R app (pronounced "you matter"), a mobile tool designed specifically for people with substance use disorders. Among 378 participants who lacked stable housing—living in shelters, on the street, in treatment facilities, or temporarily with others—those who used the app for one month reported a 50% reduction in non-opioid illicit drug use compared to those who didn't engage with it.

The results challenge a common assumption about this population. "Some people might think that these groups would not have a mobile phone or the digital literacy to use an app like this," said Eswaran, an assistant professor in WashU Medicine's Department of Emergency Medicine and the study's lead author. "But the results show people were not only using it, but also getting benefit from it."

Participants who actively messaged with trained "e-coaches" through the app's chat function saw even sharper outcomes: a 50% reduction in opioid use compared to those who didn't use the feature. Higher overall app engagement correlated with greater reductions in substance cravings and improved mental health markers tied to successful recovery—specifically, reduced feelings of being a burden to others and stronger social connection.

Born from Online Recovery Communities

The app's development traces back to 2018, when Dr. Patricia Cavazos-Rehg, a professor in WashU Medicine's Department of Psychiatry and the study's senior author, observed how people turned to social media for peer support during their most isolated moments.

"I observed how folks use social media venues to support each other, even during times when they were feeling most alone or stigmatized," Cavazos-Rehg said. "They would ask questions on social media about clinical care and seek out resources for mental health help. This inspired me to develop a tool for people who are going through mental health problems or are in recovery support."

A long-term funding commitment from the Missouri Department of Mental Health brought the concept to life. The app provides treatment locators, sobriety trackers, educational content on managing withdrawal and maintaining recovery, and weekday access to e-coaches. Participants are typically enrolled through Barnes-Jewish Hospital's emergency department or Missouri treatment centers, though word-of-mouth referrals reflect the peer-driven ethos that shaped the app's design.

Measuring Success Beyond Abstinence

The study tracked 972 enrollees between 2020 and 2024. More than 70% self-identified as having insecure housing. Of those, 378 completed follow-up surveys after one month, forming the research sample. Baseline and follow-up assessments measured substance use patterns, cravings, health literacy—the ability to find and use health information to make decisions—and two mental health indicators strongly correlated with depression: perceived burdensomeness and lack of belonging.

Users of uMAT-R showed statistically significant improvements across multiple dimensions. Beyond the reductions in drug use, participants improved their health literacy and reported lower feelings of social alienation. The chat function, which connected users to trained coaches offering encouragement and practical advice Monday through Friday, emerged as particularly effective for opioid use reduction and combating isolation.

Eswaran noted that these results demonstrate the potential of mobile health technologies to reach populations that traditional treatment systems struggle to serve. "There's potential to think creatively about how we adapt and refine tools like this even more to support vulnerable populations," she said. She is now planning a similar study for recently incarcerated people with substance use disorders.

The Treatment Access Gap

The research arrives amid a persistent contradiction in American addiction care. While drug overdose deaths declined nationally last year, substance use disorder rates continue to rise. Fewer than one in five people with substance use disorder report receiving any treatment for it, according to federal data.

The gap widens dramatically for people experiencing housing insecurity. Research consistently shows this population faces both higher overdose risk and sharply lower treatment access compared to those with stable housing. The overlapping challenges—daily survival needs, barriers to insurance, lack of transportation, and treatment facilities that require stable addresses or consistent appointment attendance—create a system that inadvertently excludes those at highest risk.

Mobile interventions offer a potential workaround. They don't require transportation, fixed appointments, or proof of address. They meet users where they are, operating on a device many already carry. The uMAT-R study suggests that assumption about digital access—that people experiencing homelessness lack smartphones or the skills to use them—may be outdated.

Cavazos-Rehg emphasized that mobile apps work best as part of a broader ecosystem. "A lot of life happens outside of traditional in-person mental health and substance use treatment settings," she said. "Mobile apps can be affordable, accessible tools that can improve the health and well-being of people, especially during critical times when other types of help may not be readily available."

What's Next

The uMAT-R app remains unavailable to the general public while the research team continues to study its effectiveness and refine its features. Current enrollment happens primarily through Missouri health care facilities, including Barnes-Jewish Hospital, where the WashU Medicine Department of Emergency Medicine's Emergency Care Research Core staff screens and enrolls participants.

Funding for the study came from the Substance Abuse and Mental Health Services Administration, the National Institute on Drug Abuse, and the National Institute of Nursing Research. The Missouri Department of Health & Senior Services continues to support the app's development.

For Eswaran, the findings confirm what she sees daily in the emergency department: people experiencing housing insecurity want help, and given the right tools, they'll use them. The challenge for public health systems is designing interventions that acknowledge the reality of their lives instead of demanding they fit into systems built for populations with stable housing, reliable transportation, and flexible schedules.

"There is a lot of overlap with people who are experiencing housing insecurity and have substance use disorders," Eswaran said. "It is important to make sure that the interventions that we provide are addressing the needs of this specific subpopulation."

The uMAT-R results suggest that addressing those needs might be simpler—and more effective—than building yet another brick-and-mortar treatment center. Sometimes the most accessible care is the kind that fits in a pocket.