An OR of 2.15 (95% CI: 0.96–4.80) was calculated for severe (≥ 3 grade) diarrhea (I2 = 29%) and 2.69 (95% CI: 1.41–5.14) for severe (≥ 3 grade) anemia (I2 = 0%) in UGT1A1*28/*28 individuals in comparison to UGT1A1 wild‐type individuals. Here, UGT1A1 is linked to anemia.