A recent preprint study from The Lancet suggests that metformin may help avoid long COVID when taken early in a COVID-19 infection.

Patients aged 30-85 who were overweight or obese, had confirmed infection with documentation, experienced symptoms that lasted no longer than seven days, had no known prior infections, and joined the trial within three days of receiving a positive test were included in the study. The metformin doses were administered over 14 days: 500 mg on the first day, 500 mg twice daily for the following 4 days, and then 500 mg in the morning and 1,000 mg in the evening for the rest 9 days.

1,125 out of the 1,323 participants volunteered to participate in long-term follow-up for COVID, including 561 in the blinded placebo group and 564 in the metformin group. The average age was 45, and 56% of the population were women, including 7% pregnant people.

Before participating in the trial, almost 55% had completed the first COVID-19 immunization, with 5.1% receiving a first booster.

A medical professional diagnosed 8.4% of individuals with long COVID overall. 6.3% of those in the metformin group developed long COVID, compared to 10.6% of those who took the placebo.

Contrary to the placebo, metformin reduced risk by 42%, which was seen in all COVID-19 variations and subgroups, including vaccination status.

The effect was possibly even more significant when metformin was taken fewer than 4 days after COVID-19 symptoms began, with a 64% reduction as opposed to a 36% reduction among those who started metformin after 4 or more days following symptoms.

To conclude Metformin caused a 42% decrease in long COVID among those with a mild to moderate COVID-19 infection.

(Source: https://www.medscape.com/viewarticle/989424?src=#vp_1)