Background/Objectives: Pain management in colorectal cancer is influenced by genetic variability in opioid receptor genes (OPRM1 and OPRD1), potentially affecting opioid efficacy and adverse drug reactions (ADRs). This study evaluated the association of OPRM1 (rs1799971 and rs510769) and OPRD1 (rs2236861) polymorphisms with pain severity, opioid efficacy, and ADRs in Chilean colorectal cancer patients. Methods: The genotypes of OPRM1 and OPRD1 polymorphisms and clinical data from 69 colorectal cancer patients were analyzed. Associations between genotypes, ADRs, and pain severity (maximum Visual Analog Scale, VAS) were evaluated under inheritance models. Results: The OPRM1 rs1799971 G allele was significantly associated with pain presence (p = 0.008), while OPRD1 rs2236861 was linked to ADR risk (p = 0.042). Allelic distribution analysis revealed higher frequencies of the OPRD1 G allele and OPRM1 rs510769 T allele in patients with ADRs and pain, respectively. For OPRM1 rs510769, the dominant model showed a significant association with pain severity (p = 0.033), while the overdominant model revealed a trend toward significance (p = 0.0504). Logistic regression model tests showed no significant predictive associations for the maximum VAS or ADRs under inheritance models. Conclusions: Genetic variations in OPRM1 and OPRD1 may play a role in pain perception and ADRs in colorectal cancer patients. These findings contribute to the understanding of pharmacogenomic factors in opioid therapy, emphasizing the need for further research to validate the clinical utility of these genetic markers.

Background/Objectives: Pain management in colorectal cancer is influenced by genetic variability in opioid receptor genes (OPRM1 and OPRD1), potentially affecting opioid efficacy and adverse drug reactions (ADR). This study evaluated the association of OPRM1 (rs1799971, rs510769) and OPRD1 (rs2236861) polymorphisms with pain severity, opioid efficacy, and ADR in Chilean colorectal cancer patients. Methods: Genotypes of OPRM1 and OPRD1 Polymorphisms and clinical data from 69 colorectal cancer patients were analyzed. Associations between genotypes, ADR, and pain severity (maximum Visual Analog Scale-VAS-) were evaluated under inheritance models. Results: The OPRM1 rs1799971 G allele was significantly associated with pain presence (p = 0.008), while OPRD1 rs2236861 was linked to ADR risk (p = 0.042). Allelic distribution analysis revealed higher frequencies of the OPRD1 G allele and OPRM1 rs510769 T allele in patients with ADR and pain, respectively. For OPRM1 rs510769, the dominant model showed a significant association with pain severity (p = 0.033), while the overdominant model revealed a trend toward significance (p = 0.0504). Logistic regression models tests showed no significant predictive associations for maximum VAS or ADR under inheritance models. Conclusions: Genetic variations in OPRM1 and OPRD1 may play a role in pain perception and ADR in colorectal cancer patients. These findings contribute to the understanding of pharmacogenomic factors in opioid therapy, emphasizing the need for further research to validate the clinical utility of these genetic markers.