patient and provider, all while consuming scarce clinical energy and laboratory resources. Diversion concerns might also contribute to a lack of buprenorphine treatment in US criminal justice settings, in which security concerns often overwhelm the public health goal of opioid treatment expansion. We expect that many providers and policy makers might find BUP-XR a meaningful improvement in this regard. Of great importance but also unclear is the relative potency of BUP-XR in suppressing the effects of fentanyl and fentanyl analogues. Illicit fentanyl continues to drive the worsening US opioid overdose epidemic. 9 Buprenorphine is a partial agonist with receptor affinity and tolerance development higher than heroin or morphine, but lower than some synthetic opioids including fentanyl derivatives such as carfentanil. Longacting buprenorphine would only provide limited protection against fentanyl if used in competitive quantities. Of course, this same limitation characterises sublingual buprenorphine, which can also simply be stopped by the individual if other opioid use is the goal. Will sustained BUP-XR blockade reduce ongoing opioid use in the first place, and therefore less heroin or fentanyl exposure overall among people in active treatment? Will it result in similar (or better) therapeutic effect than with sublingual buprenorphine because of fewer opportunities for non-adherence? We are about to find out.