Is Obesity a Factor in Lethal Opioid Toxicity?

Both obesity and opioid abuse are increasing in numbers globally. As these entities may be associated with significant respiratory compromise, it was hypothesized that synergism may occur and that as a result of this obese individuals may be more sensitive to the effects of opiates, that is, that deaths may occur at lower blood levels. To investigate this possibility, case files at Forensic Science SA, Adelaide Australia, were reviewed for all cases that occurred between 2000 and 2019 where deaths had been attributed to heroin or morphine toxicity. There were 259 cases (66 females, 193 males; age range: 18-91; average: 41.5). The average body mass index (BMI) was 26.8 (females, 26.1; males, 27.0). The total number of obese (BMI ≥ 30 < 40) decedents was 50, and the total number of morbidly obese (BMI ≥ 40) decedents was 17. No significant association was found in the obese or morbidly obese between BMI and postmortem drug levels of <0.01, ≥0.1 < 0.3, ≥0.3, <0.4, or ≥0.4 mg/L (P = 0.30, Fisher exact test). The lack of association between fatal postmortem opiate levels and BMI suggests that the negative respiratory effects of opioids and a high BMI may in some way be compensated for by as yet unidentified metabolic/pharmacokinetic factors in obesity.