ST. LOUIS — A Washington University study has found higher incidence of prescription opioid use among recovering COVID-19 patients, suggesting doctors are using the potent painkillers to treat the lingering effects of the virus — and leading the study’s main author to caution against such a trend.

The study was released last month in the journal Nature. Its main finding showed that individuals recovering from COVID-19 had an increased risk of death over the following six months, when compared with the general population. The study involved records of more than 87,000 patients who had tested positive for COVID-19 and nearly 5 million control patients in the U.S. Department of Veterans Affairs health-care databases.

But more recently, Dr. Ziyad Al-Aly, an assistant professor of medicine at Washington University and senior author of the study, has been trying to alert health-care providers of one particular finding: For every 1,000 patients, there were about nine more opioid prescriptions in the group of patients who previously had COVID-19 than in the general public.

“That, to us, raised alarms,” Al-Aly said.

The study did not look at the conditions for which doctors prescribed the medications, and Al-Aly acknowledged that further research will be needed on that point. He noted that joint and muscle pain are among the symptoms reported by people with “long COVID,” who experience the lingering and sometimes serious effects of COVID-19 for weeks or months after the initial infection.

In the Washington University study, the researchers found higher incidence of mental health issues, along with respiratory, nervous system, cardiovascular and gastrointestinal conditions.

Nine opioid prescriptions per 1,000 patients may seem like a small number, Al-Aly said, but, “given the sheer enormity of this pandemic, this is not a small number of people.”

Nationwide, more than 32.8 million have tested positive for the virus since the beginning of the pandemic.