Adolescence is a critical period for the development of association cortices. A developmental reduction in the excitation:inhibition (E:I) balance is a hallmark of critical period development, but the relationship between E:I balance and available in-vivo functional neuroimaging methods is unknown. We use pharmacological fMRI (phMRI) with an alprazolam challenge to model the effect of alprazolam-induced E:I reduction. We then apply this model to an independent developmental sample to assess developmental reductions in E:I during adolescence. We hypothesized that age was associated with multivariate patterns of GABA-modulated functional connectivity.