This parent protocol contains two components - one of which is targeting cocaine users, the other of which is targeting heavy alcohol users (who will also serve as an appropriate control group for the cocaine users - who typically have comorbid alcohol use disorders). All participants will receive one session of real and one session of sham continuous theta burst stimulation (TBS). TBS is a form of non-invasive transcranial magnetic stimulation. sham TMS on another visit (randomized). Continuous TBS is designed to lower cortical excitability, and requires a shorter stimulation period than typical low frequency transcranial magnetic stimulation (TMS). The investigators will test the hypotheses that stimulation over the medial prefrontal cortex will attenuate activity in the medial prefrontal cortex (Aim 1), using single pulse TMS in the magnetic resonance imaging scanner. Through this innovative technique it is possible to apply a single pulse of TMS to the medial prefrontal cortex and model the hemodynamic response at the stimulation site as well as monosynaptic target regions, including the striatum. The investigators will also investigate the effect of TBS on neural response to drug cues (Aim 2). The results of these aims will be further correlated with self-reported assessments of craving throughout each experimental visit. These data will be preliminary data for a subsequent R01 focused on the sustained effects of multiple sessions of TBS and their efficacy in lowering craving for extended periods of time in treatment-seekers.