A study testing drugs that are used for other conditions for their potential in treating COVID-19 has found that the antidepressant fluvoxamine (brand name Luvox) offered no benefit, at least at an initial smaller dose.

Study participants took 50 mg of the medication twice daily for 10 days, hoping to treat mild-to-moderate COVID-19 symptoms. A control group took a placebo.

"There was no evidence of improvement in time to recovery in participants who took this dose of fluvoxamine versus those who took a placebo," said investigator Dr. Adrian Hernandez, executive director of the Duke Clinical Research Institute (DCRI) in Durham, N.C.

The institute led the study in partnership with Vanderbilt University in Nashville, Tenn. It was part of ACTIV-6, a nationwide virtual study.

The researchers looked at rates of sustained recovery — or three days without symptoms. About 75% of participants were still reporting symptoms at day seven, though 82% of them reported no limitation in activities.

Nearly 70% of the 1,227 participants had received two or more doses of COVID-19 vaccine.

"This finding may reflect the decreased severity of COVID-19 symptoms in a vaccinated population," Hernandez said in a DCRI news release. "In future COVID-19 research, we may want to consider evaluating functional status instead of symptom relief."

Fluvoxamine is one of three U.S. Food and Drug Administration-approved repurposed medications being tested in ACTIV-6. A selective serotonin reuptake inhibitor used to treat obsessive-compulsive disorder and depression, it was chosen because previous evidence suggested it might reduce inflammation from the virus.

The ACTIV-6 team is also testing the drug at a different dose — 100 mg twice daily for 13 days.

"Other research suggests that 100 mg of fluvoxamine taken twice daily may be effective in treating COVID-19, but tolerance may be a limitation," said Dr. Susanna Naggie, who oversees the study's clinical coordinating center. "We set out to test if 50 mg taken twice daily is effective and tolerated. We learned efficacy is not achieved at the lower dose of fluvoxamine and look forward to learning of and sharing results from the open study arm testing the higher dose."

The study findings were published Oct. 18 in medRxiv, a pre-publication server. They have been submitted to a peer-reviewed journal.