The levels of primary DNA damage measured in hepatocytes of male Wistar rats using the alkaline comet assay after 1-, 3-, and 7-day treatments with irinotecan (IRI), Δ9-tetrahydrocannabinol (THC), their combination (IRI + THC), and in the respective controls. Legend: IRI was administered once, via an intraperitoneal injection at a dose of 100 mg/kg b.w.; THC was dissolved in sesame oil and administered daily per os at a dose of 7 mg/kg b.w.; control rats were given the same daily volume of sesame oil as the THC group. Data are reported as mean/median values, and ranges (Min.—minimum value; Max.—maximum value) of one thousand independent comet measurements per each experimental group (200 comets/rat were scored on duplicate slides). Significantly different (p < 0.05, ANOVA with post hoc Tukey HSD test) compared to C—control; T—THC; &—combination of IRI and THC; I—1-day treatment; II—3-day treatment; III—7-day treatment.