Cannabidiol in Opioid Use Disorder and Chronic Pain

Inclusion Criteria: * Males and females, Veterans and non-Veterans, aged between 18 and 70 years old. * Diagnosed with OUD and currently enrolled in methadone maintenance treatment. * Having chronic pain, uniformly operationalized as grade II (high-intensity) non-cancer pain for ≥ 6 months. * Capable of providing informed consent in English. * Compliant in opioid maintenance treatment and on a stable dose for four weeks or longer. * Not meeting DSM-5 criteria for substance use disorders other than OUD or tobacco use disorder within the last 12 months. * No current medical problems deemed contraindicated for participation by principal investigator. * For women, not pregnant as determined by pregnancy screening; not breast-feeding; using acceptable birth control methods. Acceptable contraception for females includes oral contraceptives, contraceptive depot injections, contraceptive subdermal implants, intrauterine devices, or surgical contraception methods. Acceptable contraception for males includes condoms or surgical contraception methods. Exclusion Criteria: * Other current major psychiatric disorders deemed clinically unstable by the principal investigator, such as severe depression and/or active suicidal ideation. * Having experienced major psychosocial stressors recently (≤ 6 weeks before enrollment), at the discretion of the principal investigator. * Methadone dose under 30 mg or over 150 mg/day. * Having received inpatient psychiatric treatment recently (≤ 60 days before enrollment). * Candidates receiving products containing either THC or CBD will be excluded. All participants will be asked to abstain from cannabinoids. Prior to receiving the study medication on the first test session, participants' cannabinoid use will be assessed using a quantitative point-of-care urine 11-nor-9-carboxy-THC concentration test with a cut-off of ≤ 50 mg/mL. If a participant tests greater than ≤50 mg/mL, they will be asked to abstain for an additional 7 to 14 days. If 14 days after their initial THC concentration test the participant continues to test positive, they will not be allowed to participate in the study. * A physician will carefully evaluate participants for use of over-the-counter or prescription psychoactive drugs known to affect pain threshold or pain tolerance (including NSAIDS, serotonin-norepinephrine reuptake inhibitors (SNRIs) (e.g. venlafaxine, duloxetine), gabapentinoids, tricyclic antidepressants (e.g., nortriptyline, amitriptyline), anticonvuls…