Cocaine abusers who maintain high levels of the μ-opioid receptor in their brain during early abstinence relapse sooner than abusers whose levels drop. Dr. J. James Frost of the Johns Hopkins University School of Medicine and Dr. David A. Gorelick of NIDA's Intramural Research Program (IRP) and colleagues used positron emission tomography and a radiotracer ([11C]carfentanil) to measure μ-opioid receptor levels in 15 cocaine abusers who agreed, for a fee, to stop taking the drug and live in a supervised clinical research facility for 3 months. After discharge, the participants reported on their drug use and submitted periodic urine samples for a year.
During the 3 months of monitored cocaine abstinence at the research facility, μ-opioid receptor levels decreased in the frontal and temporal regions of the cortex. Participants who showed lesser decreases during this period tended to experience earlier relapse—as defined by two consecutive days of cocaine use—after leaving the facility. Higher μ-opioid receptor levels at the time of leaving were also associated with more days of cocaine use in the first month following a relapse.
In a study conducted with IRP colleagues Drs. Udi Ghitza and Kenzie Preston, the research team reported similar findings among a group of cocaine abusers participating in 12 weeks of medication-free psychosocial outpatient treatment. The researchers suggest that receptor levels may influence relapse by mediating craving.