During the screening period (Study Days -3 and -2), the urine drug screen (UDS) must be negative for cocaine and opioids, and the self-reported last use of cocaine or opioids must be at least seven days prior to this result, in order to ensure that possible cocaine or opioid withdrawal has ended. After these criteria have been met, all subjects will receive placebo at 8:30 AM for one day during the Placebo Pretreatment Baseline Day (Study Day -1). The first fMRI session (fMRI #1) will take place at 10:00 AM on the following day (Study Day 1). Following fMRI #1, the subjects will be randomized into two parallel groups (Group A: Lorcaserin; Group B: Parallel Placebo). Based on the information that a lower dose of lorcaserin has the potential to be clinically effective , and based on the safety and abuse potential data from human studies, as well as the preclinical data on interaction with cocaine , the study will begin with the lower dose of lorcaserin (10 mg per day). For Group A (lorcaserin group), the lorcaserin dose will be 10 mg orally per day for 7 days. For Group B (parallel placebo group), identical appearing placebo will be given orally according to the same schedule as lorcaserin for 7 days. After the 7 days of treatment with study medications, fMRI #2 will take place, then study medications will be discontinued. A follow-up visit will occur one week after the last dose of study medication. See Section II.b for details and criteria for stopping or continuing this dosage based on the results of the interim analysis, which will take place after 15 subjects have completed at each arm. Based on the interim analysis, if there is no significant effect and no trend towards significant effect (p > 0.10) for the lower dose lorcaserin in the primary regions of interest for the cue-reactivity fMRI task, and no significant accumulation of adverse effects, then testing will stop for the lower dose of lorcaserin, and testing will begin for the higher dose of lorcaserin (10 mg twice per day) 7 days. The higher dose of lorcaserin will be tested in a two group parallel arm design, initially with 15 subjects in the high dose lorcaserin arm and 15 subjects in the parallel placebo arm. Another interim analysis will take place after 15 subjects have completed at each arm in the higher dose lorcaserin study.