Rationale <p>Drug relapse among individuals with substance use disorders can be triggered by social cues that were present in the original drug-taking environment. Previous preclinical work demonstrated this process using the ABA renewal design in which rats were first trained to lever press for contingent cocaine with a peer (context A), then the response was extinguished without the peer (context B), and finally responding was shown to return or renew with re-presentation of the peer (context A).</p> Objective <p>This study sought to determine if the presence and/or absence of a peer would differentially elicit cocaine and fentanyl seeking.</p> Methods <p>In 4 separate experiments, rats were tested for either ABA or BAB renewal of either cocaine seeking (Experiments 1A and 1B) or fentanyl seeking (Experiments 2A and 2B). In addition, in the fentanyl experiments, naltrexone (0.1-1&#xa0;mg/kg) was administered prior to both ABA and BAB renewal tests to determine if renewal of fentanyl seeking was altered. An additional experiment (Experiment 2C) tested the effect of naltrexone (0.1-1&#xa0;mg/kg) on locomotor activity.</p> Results <p>Results showed that cocaine seeking was obtained using either ABA or BAB renewal designs, whereas fentanyl seeking was obtained only using the ABA renewal design. In addition, ABA renewal of fentanyl seeking was decreased by naltrexone at a dose (1&#xa0;mg/kg) that had no effect on locomotion.</p> Conclusions <p> These results indicate that peer presence can trigger both cocaine and fentanyl seeking, whereas peer absence specifically triggers cocaine seeking. ABA renewal of fentanyl seeking was decreased by naltrexone, indicating that opiate receptors are involved.</p>