For both the cocaine sub study and the alcohol sub study: Drug Screens: A multidrug urine panel will be given to all participants at the screening visit and each scanning/stimulation visit. In order to minimize any potential risk of this session of theta burst stimulation, participants must have a negative urine drug screen for stimulants (including cocaine, amphetamine, methamphetamine) at the Scanning/Stimulation visits and have no signs of alcohol withdrawal. Based on the sensitivity of this test, this will require that the participants abstain from cocaine use for 48 hours prior to the intervention. While there are no reports of adverse events from transcranial magnetic stimulation in cocaine users this precaution is being taken as psychostimulants are known to reduce the seizure threshold. Participants will be informed of this at the Screening visit. If they attend a Scanning/Stimulation visit and have a positive urine drug screen, they will be given an opportunity to reschedule.