Polysubstance use is common among opioid-using women, yet its association with pharmacotherapy for neonatal abstinence syndrome (NAS) remains unclear. We hypothesized that benzodiazepine exposure would increase risk of an infant developing pharmacologically treated NAS. We conducted a retrospective cohort study of maternal-infant dyads enrolled in Tennessee Medicaid, using individual-level data linkage of vital records and administrative (ie, outpatient, inpatient, and prescription) data from 2009 to 2011. These data underwent chart review from 2013 to 2016 to obtain clinically relevant exposure data (eg, toxicology testing). The association of antenatal exposures with pharmacologically treated NAS was evaluated by using multivariable logistic regression, controlling for maternal and infant factors and clustered by hospital. Among 112 029 maternal-infant dyads, we confirmed 822 cases of NAS, of which 598 (72.7%) were cases of pharmacologically treated NAS. Infants who developed pharmacologically treated NAS were more likely to have been exposed to antenatal benzodiazepines compared with infants with confirmed NAS not treated pharmacologically (40.9% vs 30.8%; P = .008). In adjusted analyses, benzodiazepine exposure was associated with greater risk of developing pharmacologically treated NAS (odds ratio: 1.51; 95% confidence interval: 1.04-2.21). Alternatively, exposure to tobacco, marijuana, cocaine, gabapentin, and selective serotonin reuptake inhibitors were not associated with increased risk of developing pharmacologically treated NAS. Among a population of infants with intrauterine polysubstance exposure, benzodiazepine exposure was an independent predictor of an infant developing pharmacologically treated NAS. Obtaining history of antenatal benzodiazepine exposure among opioid-exposed infants may allow for risk stratification and development of personalized care plans.