Combined with the high selectivity of [11C]-carfentanil for the MOR (Ki = 0.0024 nM) over delta opioid (Ki = 3.28 nM) and kappa opioid receptors (Ki = 43.1 nM), our data indicate a lower MOR availability in schizophrenia patients46. Here, OPRK1 is linked to schizophrenia.