The purpose of the study is to examine whether an investigational medication called ketamine is able to improve treatment outcomes for concurrent opioid addiction and depression when used in conjunction with standard of care medications (such as buprenorphine, methadone or naltrexone). Study medications will be delivered twice per week for four weeks. If you are eligible and you decide to enroll in the study, your participation will last approximately 8-12 weeks, or 2-3 months.