Reduced inhibition as shown though GABA-edited MRS and TMS measures have been suggested to underlie some of the symptomology of ADHD. In this study we apply GABA-MRS and single- and paired-pulse TMS in ADHD and typically developing cohorts to better understand altered inhibition in ADHD. We show that SICI approaches 1 with increasing GABA across both groups. Secondly, we show a convergence in SICI and single-pulse TMS responses with increasing GABA. Last, we show different factors modulate the TMS responses between ADHD and control suggesting there are additional differences in GABAergic inhibition between these two groups.