Concomitant drugs with buprenorphine user deaths

•There were no death cases with buprenorphine as the only toxicological finding.•Extensive concomitant benzodiazepine use was found regardless of the cause of death.•The most prevalent benzodiazepines were clonazepam, alprazolam and diazepam.•Buprenorphine poisonings increased annually in age group 15−24 y.•Benzodiazepines and illicit drugs were more common in age group 15−24 than 25−64 y. Buprenorphine is abused in several countries notwithstanding its benefits as an analgesic and as an opioid agonist treatment medication. Benzodiazepines and alcohol have previously been associated with buprenorphine toxicity. This study elucidates the role of emerging concomitant drugs in different groups of buprenorphine user deaths. All cases in the Finnish national post-mortem toxicology database from 2016–2019 in which buprenorphine or norbuprenorphine was a laboratory finding in any post-mortem specimen and age at death of 15–64 years were investigated for cause and manner of death, concurrent drug and alcohol findings, age, and gender. There were 792 deaths with a buprenorphine finding, of which buprenorphine was implicated in poisoning without other opioids in 271 cases (34 %). In this group of buprenorphine poisoning deaths, concomitant benzodiazepines were found in 94 % (clonazepam 53 %), illicit drugs in 63 %, gabapentinoids in 50 % (pregabalin 41 %), alcohol in 41 %, antidepressants in 32 %, and antipsychotics in 28 % of cases; only three deaths showed no benzodiazepines, alcohol, or gabapentinoids. Polydrug use was common regardless of the cause of death. In the age group 15 to 24 years, concomitant use of benzodiazepines and illicit drugs, and buprenorphine poisoning were more prevalent than in the age group 25–64 years. The unprecedentedly high concomitant use of benzodiazepines in buprenorphine user deaths obscures other possible pharmacological risk factors for buprenorphine poisoning that could be relevant for prevention. Higher mortality in the younger age group suggests particularly unsafe drug use patterns that should be addressed.