Methadone and buprenorphine-related deaths among people prescribed and not prescribed Opioid Agonist Therapy during the COVID-19 pandemic in England

•Methadone-related mortality grew by 64% in the first wave of the COVID-19 pandemic and this increased occurred in cases where there was no methadone prescription at time of death.•This change occurred despite no apparent decrease in numbers in treatment for opioid use disorder.•Prescribed and non-prescribed buprenorphine-related mortality remained low and did not significantly change.•There were no changes in the rates of co-detections of other opioids, benzodiazepines or alcohol.