“I just know my main goal is to remain sober and recover all my relationships and have that sense of normalcy in my life,” Ms. Steenhoek said. “That’s what I want more than anything right now.”

Dr. Gastala increased her daily dose to 12 milligrams, from eight.

“If you feel it’s not enough, don’t wait until your next appointment,” she said. “Call us.”

An Unexpected Mission

Dr. Gastala had no interest in treating addiction until she arrived in rural Iowa, but she knew from a young age that she wanted to do work that others might shy away from. She was 6 when her mother, a secretary, died of Hodgkins lymphoma, and the doctors and nurses who cared for her left a profound mark. When she was in medical school in Chicago, her father, an engineer, died of brain cancer, and she decided to spend four months working at a rural clinic for the poor in Bolivia. The experience, she said, propelled her into family medicine.

She came to Marshalltown straight out of residency at the University of Iowa, as a participant in a federal program that would help pay off her medical school loans if she worked for three years in an underserved community. Marshalltown, a city of 27,000, appealed because of its diverse population — a mix of longtime, mostly white residents and Hispanics who started coming in the 1980s to work in the area’s meatpacking plants.

Dr. Gastala was eager to start the type of weight-loss and diabetes prevention programs here that she had organized as a resident in Iowa City. But after arriving in July 2015, she was struck by the number of patients dependent on opioids they’d been prescribed over the years — including at her new practice — for chronic pain.

Iowa is no Ohio or West Virginia in the breadth of its opioid problem; meth addiction remains more common here. Heroin and fentanyl, however, have started to grab hold. Iowa had 206 deaths involving opioids in 2017, according to provisional state data; fatal heroin overdoses more than doubled, to 34.