Catecholamines and amino acid transmitter systems are known to interact, the exact links and its impact on cognitive control functions is unclear. Using a multi-modal imaging approach combining EEG and Proton-magnetic resonance spectroscopy ( 1H-MRS), we investigated the effect of different degrees of pharmacological catecholaminergic enhancement onto theta band activity (TBA) as a measure of interference control during response inhibition and execution. Central to our study was evaluating the predictive impact of in-vivo baseline GABA+ concentrations, under varying degrees of Methylphenidate (MPH) stimulation, in the striatum, the anterior cingulate cortex (ACC) and the supplemental motor area (SMA) of healthy adults. We provide evidence for a predictive interrelation of baseline GABA+ concentrations in cognitive control relevant brain areas, onto task induced TBA during response control stimulated with MPH. Baseline GABA+ concentrations in the ACC, the striatum, and the SMA had differential impact on predicting interference control-related TBA in response execution trials. GABA+ concentrations in the ACC appeared to be specifically important for TBA modulations when the cognitive effort needed for interference control was high - that is when no prior task experience exists, or in the absence of catecholaminergic enhancement with MPH. The study highlights the predictive role of baseline GABA+ concentrations in key brain areas influencing cognitive control and responsiveness to catecholaminergic enhancement, particularly in high-effort scenarios.