Table 2.

Estimates of colorectal cancer risk associated with metformin use

Metformin useNo. of eventsPerson-yearsAdjusteda HR (95% CI)
 Never487257,530.931.00 (reference)
 Ever325170,921.000.90 (0.76–1.07)
Total duration (y)
 <2.010461,029.820.88 (0.70–1.10)
 2.0–4.912256,393.231.02 (0.81–1.27)
 ≥5.09953,497.950.78 (0.60–1.02)
Ptrend =0.17
Recency of use
 Former7433,469.110.90 (0.68–1.19)
 Recent3421,468.900.75 (0.52–1.07)
 Current
 <5.0 years14375,344.550.98 (0.80–1.21)
 ≥5.0 years7440,638.440.78 (0.59–1.04)
Ptrend = 0.23
Cumulative dose (mg), quartiles
 ≤750,0009455,340.380.85 (0.68–1.10)
 750,001–2,300,00010952,092.480.99 (0.78–1.24)
 2,300,001–4,930,0008741,074.690.95 (0.73–1.24)
 >4,930,0003522,413.440.67 (0.45–0.98)
Ptrend =0.18
  • aAdjusted for gender, race/ethnicity, birth year, diabetes duration, BMI, alcohol use, smoking status, Charlson comorbidity index, education, income level, creatinine, HbA1c, history of lower endoscopy (all fixed at baseline); first lower endoscopy after baseline (time-varying) and use of other types of diabetes medications (time-varying).