The primary purpose of this study is to investigate the effect of lorcaserin on reductions in
cannabis use and multiple constructs of impulsivity in outpatient treatment-seeking
individuals with cannabis use disorder (CUD). Additionally, the investigators will make use
of the technological application of ecological momentary assessments (EMA), to collect
real-time data at key time intervals during the study on participants' use of cannabis and
other substances in addition to measuring impulsive traits through self-initiated, fixed and
random phone prompts. This will be a 13-week randomized, double-blind, placebo-controlled
trial, with week 1 focused on baseline assessments of impulsivity (through EMA in vivo and at
study visits), weeks 2- 3 of medication lead-in, and week 4 targeting a reduced cannabis
use/quit day through week 13. The primary aims are to (1) Examine the effect of lorcaserin
compared to placebo, on reductions in cannabis use among treatment-seeking outpatients with
CUD, (2) Examine the effect of lorcaserin compared to placebo on behavioral and self-report
measures of impulsivity among individuals with CUD during the medication lead-in phase (weeks
2-3). The secondary aim is to examine whether reductions in impulsivity (during weeks 2-3)
mediates the effect of lorcaserin on cannabis use (during weeks 8-13), if the primary
hypotheses are supported. Finally, the investigators will explore the effect of lorcaserin
compared to placebo on (1) drop-out rates, (2) time to discontinuation from study, (3)
treatment adherence, and (4) nicotine use.