STUDY DESIGN. This is a 12 week, 2 group randomized controlled trial that will be completed in an outpatient setting. Eligible participants will be randomized to D-serine or matching placebo and will be scheduled to attend three research visits per week throughout the active treatment phase which begins with randomization and ends on day 7 of study week 12. A single visit will be scheduled in week 13 to complete retrospective data for week 12. Participants will receive D-serine or placebo throughout the 12-week active treatment phase. Randomization will be in a 1:1 ratio, stratified by cocaine use frequency (<10 days or ≥ 10 days in the 28 days prior to consent).