Opioid Use Disorder (OUD) and opioid-related deaths remain a major public health concern in the United States. Both environmental and genetic factors influence risk for OUD. We previously identified Hnrnph1 as a quantitative trait gene underlying the stimulant, rewarding, and reinforcing properties of methamphetamine. Prior work demonstrates that hnRNP H1, the RNA-binding protein encoded by Hnrnph1, post-transcriptionally regulates Oprm1 (mu opioid receptor gene) – the primary molecular target for the therapeutic and addictive properties of opioids. Because genetic variants can exert pleiotropic effects on behaviors induced by multiple drugs of abuse, in the current study, we tested the hypothesis that Hnrnph1 mutants would show reduced behavioral sensitivity to the mu opioid receptor agonist fentanyl. Hnrnph1 mutants showed reduced sensitivity to fentanyl-induced locomotor activity, along with a female-specific reduction in, and a male-specific induction of, locomotor sensitization following three, daily injections (0.2 mg/kg, i.p.). Hnrnph1 mutants also required a higher dose of fentanyl to exhibit opioid reward as measured via conditioned place preference. Male Hnrnph1 mutants showed reduced fentanyl reinforcement. Hnrnph1 mutants also showed reduced sucrose motivation, suggesting a reward deficit. No genotypic differences were observed in baseline thermal nociception, fentanyl-induced antinociception, physical or negative affective signs of opioid dependence, or in sensorimotor gating. In the context of our prior work, these findings suggest that Hnrnph1 dysfunction exerts a selective role in reducing the addiction liability to drugs of abuse (opioids and psychostimulants), which could provide new biological pathways to improve their therapeutic profiles.