Metformin within 6 days of COVID linked to 53% lower long COVID or death risk in target trial emulation

Researchers emulated a target trial using electronic health records, matching 248 patients receiving new metformin prescriptions to 248 controls given fluvoxamine, fluticasone, ivermectin, or montelukast within six days of documented infection. Most cases occurred during Omicron circulation. Weighted six-month incidence of long COVID or death reached 4.0% with metformin versus 8.5% in controls, yielding an absolute reduction of 4.5 percentage points. The design adjusted for measured confounders but could not eliminate residual bias from unmeasured factors such as adherence or prescribing intent.

This finding aligns with the earlier COVID-OUT randomized trial, which reported reduced acute severity and hospitalization with metformin, and a UK target trial showing a hazard ratio of 0.36 for metformin initiated within 90 days. Metabolic modulation of inflammation and viral persistence offers a plausible mechanism, yet the current study remains observational. No large pragmatic RCT has yet tested early outpatient metformin specifically for long COVID prevention.

Next steps require a multicenter randomized trial powered for long COVID incidence with standardized outcome ascertainment and extended follow-up beyond six months. Regulators and guideline panels will need replicated interventional data before changing prescribing recommendations for non-diabetic patients.