← Metformin × adverse events & safety

SynthesisCancer reports (Hoboken, N.J.)2026

Association Between Metformin Use and Risk of Lung Cancer in Patients With Type 2 Diabetes: A Systematic Review and Meta-Analysis.

Mehdi Karimi et al.PubMed ↗Full text ↗Publisher ↗

  • Metformin userslooks good hereLower lung cancer risk.Correlation only, not a test of it.
  • Extended Metformin use (>  3 years)looks good hereLower lung cancer risk.Correlation only, not a test of it.

What moved togetherboth groups pooled, not the treatment’s effect

Correlation, not cause

Metformin users went with lower lung cancer risk

−15%−23% to −6%

Metformin users vs nonusers

Bigger than 4 in 10 for adverse events & safety

As reported

HR 0.85, 95% CI 0.77–0.94

Correlation, not cause

Metformin users went with lower lung cancer risk

−21%−30% to −11%

Metformin users vs nonusers, in cohort studies

Bigger than 5 in 10 for adverse events & safety

As reported

HR 0.79, 95% CI 0.70–0.89

Correlation, not cause

Metformin users went with lower lung cancer risk

−18%−32% to −1%

Metformin users vs nonusers, in studies conducted in Asia

Bigger than 5 in 10 for adverse events & safety

As reported

HR 0.82, 95% CI 0.68–0.99

+1 more in the walkthrough ↓

Who was studied, and how

people with type 2 diabetes, in this paper

Already taking Metformin users, or nottheir own situation, not assigned

on Metformin users
nonusers

Metformin users went with lower lung cancer risk−15%

correlation, not a test

Already taking Extended Metformin use (>  3 years), or nottheir own situation, not assigned

on Extended Metformin use (>  3 years)
nonusers

Extended Metformin use (>  3 years) went with lower lung cancer risk−13%

correlation, not a test

the abstract, start to end

… users compared with nonusers (HR: 0.85, 95% CI: [0.77-0.94], …

… associations in cohort studies (HR: 0.79, 95% CI: [0.70-0.89], p < 0.01) and in studies conducted in Asia (HR: 0.82, 95% CI: [0.68-0.99], …

… reduction in lung cancer risk (HR: 0.87, 95% CI: [0.79-0.95]; …

← favours treatmentfavours comparator →
could be chance
Lung cancer riskMetformin users vs nonusers
HR 0.850.77–0.94
Lung cancer riskMetformin users vs nonusers, in cohort studies
HR 0.790.70–0.89
Lung cancer riskMetformin users vs nonusers, in studies conducted in Asia
HR 0.820.68–0.99
Lung cancer riskExtended Metformin use (>  3 years) vs nonusers
HR 0.870.79–0.95
MetforminAdverse events & safety
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Full record →Abstract, authors, funding and every citing paper · PMID 42581008