Inclusion Criteria:  Men and women aged 18-75, inclusive. Endorsing > 6 months of CNCP. On stable prescription opioid doses of at least 25 MME for >90 days. Either no prior use or current light cannabis use (weekly or less in the past 12 months). Desire to use medical cannabis for pain to control pain and/or reduce opioid dose. Competent and willing to provide written informed consent in English. Potential participants of childbearing potential must have a negative urine pregnancy test at enrollment and agree to use effective contraception: abstinence; hormonal contraception; intra-uterine device, sterilization; or double barrier contraception, during the study.  Exclusion Criteria:  Current cannabis use of greater than weekly on average in the past 12 months, assessed via self-report. Current major medical illness, such as cancer, symptomatic hypothyroidism/hyperthyroidism or severe respiratory compromise. Use of non-prescribed opioids, by self-report or urine toxicology screen. Actively suicidal and/or suicide attempt or psychiatric hospitalization in past year, or current suicidal ideation with specific plan or intent. History of intellectual disability (e.g., Down's syndrome) or other severe developmental disorder or IQ < 70. Current diagnosis of delirium, dementia, amnestic, or other cognitive disorder; lifetime schizophrenia or other psychotic disorder; bipolar I disorder; clinically significant diagnosis of borderline, antisocial, paranoid, schizoid, schizotypal or histrionic personality disorder. Surgery within the past month or planned during the next 6 months. Pregnant or trying to get pregnant or breastfeeding. In the opinion of the investigator or study physicians, not able to safely participate in this study.