(NewsNation) — A commonly used diabetes drug could help decrease the risk of long COVID, according to preliminary data from a clinical trial.

Long COVID has been dubbed by many doctors as a medical “mystery” wherein symptoms linger for months after a patient has been infected. The Centers for Disease Control and Prevention estimates up to 20% of COVID patients have long-lasting symptoms, though other studies put the number closer to 3%.

Researchers set out to identify whether any medications were effective in preventing long COVID, and settled on three to test: metformin, ivermectin and fluvoxamine. The data, published in a pre-print Dec. 24 on medRxiv, concluded that metformin, a commonly prescribed diabetes drug, decreased the incidence of long COVID by 42%.

The study split 1,125 adults into six groups, with half receiving metformin with a placebo or a combination of the other drugs. The other half received a placebo with either another placebo or a combination of the other drugs.

After day 300, or roughly 10 months, 6.3% in metformin group had received a long COVID diagnosis, compared with 10.6% of the control group. That’s about a 42% decrease in symptoms.

Overall, 8.4% of the 1,125 participants reported a long COVID diagnosis by a doctor. The sample was mostly vaccinated and included enrollment during the omicron wave, which was highly contagious.

“This is notable because Long Covid is a significant public health emergency that may have lasting health, mental health, and economic sequelae, especially in socioeconomically marginalized groups,” the trial’s authors stated. “Further clinical trials are warranted to assess whether there is synergy with other treatments, such as nirmatrelvir in vaccinated populations or in those with prior Covid-19.”

Notably, the study concluded that fluvoxamine and ivermectin did not decrease the development of long COVID, nor did they decrease the likelihood of severe COVID-19 outcomes (such as hospitalization or death) within the first 14 days of an infection. Ivermectin is an anti-parasite drug, and the CDC and the Food and Drug Administration warned against the use of it after it was suggested on the internet as a viable COVID treatment.

The long COVID diagnoses for the ivermectin group and its control were roughly the same (8% vs. 8.1%), while the fluvoxamine group reported a higher incidence of long COVID than its control, at 10.1% to 7.5%.

While the data could shed light on a path forward for long COVID treatment, the authors emphasized the need for more studies.

“Future research is needed to understand optimal dosing regimens for preventing Long Covid, whether extended release is effective in persons who have side effects from immediate release metformin, and whether metformin could be used as a treatment for Long Covid,” the researchers wrote. “Future research could also assess whether metformin is effective if started during an emergency department visit or hospitalization for Covid-19.”