Recent research suggests that a new kind of treatment, repetitive transcranial magnetic stimulation (rTMS) can help people with substance use disorders cut down or quit using. This study seeks to recruit individuals who are currently heavy marijuana users who are attempting to cut down or quit using marijuana. Participants will have 20 treatments of active or sham rTMS over 10 visits. In addition to having a 50% chance of receiving rTMS, participants will be given behavioral counseling. Participants who received sham rTMS will have the opportunity to receive active rTMS after they complete the study.