The opioid epidemic is a rapidly evolving societal issue driven, in part, by a surge in synthetic opioid use. A rise in fentanyl use among pregnant women has led to a 40-fold increase in the number of perinatally-exposed infants in the past decade. These children are more likely to develop mood- and somatosensory-related conditions later in life, suggesting that fentanyl may permanently alter neural development. Here, we examined the behavioral and synaptic consequences of perinatal fentanyl exposure in adolescent male and female C57BL/6J mice and assessed the therapeutic potential of environmental enrichment to mitigate these effects. Dams were given ad libitum access to fentanyl (10 µg/mL, per os ) across pregnancy and until weaning (PD 21). Perinatally-exposed adolescent mice displayed hyperactivity (PD 45), enhanced sensitivity to anxiogenic environments (PD 46), and sensory maladaptation (PD 47) – sustained behavioral effects that were completely normalized by environmental enrichment (PD 21-45). Addi...