This is a randomized, placebo-controlled, crossover human laboratory study investigating the dose-dependent safety and acute effects of Cannabidiol (CBD) on measures of pain and opioid craving in outpatients with opioid use disorder (OUD) receiving medication-assisted treatment with methadone or buprenorphine. With a duration of approximately 4 weeks, participants will come to the testing site for a total of five times: one initial screening session, and four experimental sessions where study medication, CBD, will be administered, separated by at least 72 hours to limit carryover effects.

Thirty-four male and female (ages 18-70) participants with comorbid opioid use disorder (OUD) and non-cancer chronic pain for at least 6 months, currently receiving methadone (n= 22) or buprenorphine (n= 12), will be enrolled. Across four test sessions, prior to their daily methadone or buprenorphine dose, and thus at trough plasma levels of opioid, participants will receive oral CBD (400 mg, 800 mg, 1200 mg) or placebo. Subsequently, all participants will undergo laboratory testing of opioid-related outcomes.

Pain sensitivity will be measured using Quantitative Sensory Testing (QST), the Pain Catastrophizing Scale (PCS), and a pain Visual Analog Scale (VAS). Attentional bias and cue-induced opioid craving will be measured using a visual probe task and the Heroin Craving Scale (HCQ-14). Subjective opioid withdrawal symptoms will be assessed using the Subjective Opiate Withdrawal Scale (SOWS). Abuse potential will be measured using the Drug Effects Questionnaire (DEQ). Negative affect will be measured using the Positive and Negative Affect Schedule (PANAS). Cognitive performance will be measured by a comprehensive cognitive battery that includes the Continuous Performance Test (CPT) and the Hopkins Verbal Learning Test (HVLT). Safety will be thoroughly measured with the Systematic Assessment for Treatment Emergent Events (SAFTEE) for adverse effects.

The order of study medication administration will be counterbalanced order to minimize carryover effects. On the initial screening day and at the end of medication treatment, blood will be drawn to determine serum drug levels. Participants will be thoroughly evaluated by a physician prior to discharge on each experimental session. One week after the last study medication dose, participants will be conducted by phone for a follow-up session.

Inclusion Criteria:

• Males and females, Veterans and non-Veterans, aged between 18 and 70 years old.
• Diagnosed with OUD and currently enrolled in methadone or buprenorphine 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.
• Buprenorphine dose over 24 mg per 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), anticonvulsant medications (e.g., topiramate, carbamazepine)). Only participants who are on stable doses (i.e., consistent daily administration of the medication for at least three months at the same dose following the last dose change, either increase or decrease) of these medications, and whose dosing schedules allow participation in the study visits, thus excluding instances of single-dose or temporary dosing of the medication, will be eligible as determined by principal investigator. If possible, the morning dose will be administered after the study visit.
• Current, regular use of benzodiazepines, other prescription opioids, or platelet inhibitors (e.g., clopidogrel, apixaban, ticagrelor).
• Current weight of less of 60 kg.
• Allergy to sesame seed oil, which is an ingredient of the CBD formulation used.
• Serious medical or neurological illness or treatment for a medical disorder that could interfere with study participation as determined by principal investigator.
• Participants who have elevation of liver enzymes (ALT and/or AST) 2x above the normal limit or higher.
• Contraindications for exposure to cold temperatures, such as Raynaud's phenomenon and hypertension.

Participants will receive CBD (400 mg, 800 mg, 1200 mg) or placebo.