The goal of this research study is to examine the endocannabinoid (eCB) function in vivo in individuals with opioid use disorder (OUD) by measuring cannabinoid receptor 1 (CB1R) availability.

The investigators will image brain cannabinoid receptors using Positron Emission Tomography (PET) imaging and the radioligand [11C] OMAR, in healthy individuals and individuals diagnosed with opioid use disorder. Research participants may complete screening, MRI, PET scan and follow up visits.

Inclusion Criteria:

• Able to provide informed consent
• Male and female 18 years and older
• DSM-5 diagnosis of opioid use disorder (for OUD group)
• Physically healthy i.e., no clinically unstable medical conditions
• Written informed consent and have capacity to consent and comply with study procedures

Exclusion Criteria:

• Current neuro-psychiatric illness or severe systemic disease (opioid use disorder is permitted in the OUD group).
• Presence of ferromagnetic metal in the body or heart pacemaker
• Have had exposure to ionizing radiation that in combination with the study tracer would result in a cumulative exposure that exceeds recommended exposure limits
• Are claustrophobic