High BMI is a specific risk factor for drug-related mortality in patients receiving methadone: A case control study

Long-term treatment of opioid dependence with the opioid agonist therapy (OAT) methadone can lead to significant weight gain. This study investigated whether OAT patients with a body mass index (BMI) deemed overweight (≥25) are at increased risk of mortality.

A retrospective case-control study was performed with anonymised data collected from living and deceased persons registered as receiving OAT from Derbyshire or Teesside drug and alcohol services in the United Kingdom. Height, weight, age, gender, OAT type and dose, smoking status and postcode of usual address were collected. Cause of death was collected from deceased individuals. Adjusted odds ratios (aOR) and 95% confidence intervals (95% CI) were calculated using regression models.

Data were collected for 1574 living and 233 deceased individuals. Mean BMI of all individuals (25.75 ± 6.56) was above the threshold considered a healthy weight, and was higher in deceased (26.63 ± 7.87) than living individuals (25.61 ± 6.34; P < 0.05). A BMI of 30 corresponded to an average 7.7% increased risk of mortality, increasing to 37.2% for those with a BMI of 35 and 107.3% for those with a BMI of 40. Risk of death also increased by an average of 43.6% for those deemed underweight (BMI 15). People who were older (mean aOR = 1.019; 95% CI = 1.002-1.036), smoked (mean aOR = 2.917; 95% CI = 1.726-4.934) and lived in more deprived areas (mean aOR = 0.891; 95% CI = 0.831-0.956) were more likely to have died, as were those prescribed methadone (vs buprenorphine) (mean aOR = 1.916; 95% CI = 1.138-3.227). There was no significant effect of gender (mean aOR = 0.844; 95% CI = 0.612-1.162) or methadone dose (aOR = 0.995; 95% CI = 0.988-1.001) on incidence of death. Acute drug toxicity was the predominant underlying cause of death for healthy and overweight people (46% of cases in both groups), with cancer (21% of cases) and infection (18% of cases) greater contributors to cause of death in underweight people.

Opioid agonist therapy (OAT) patients with a body mass index outside of the 'healthy' range appear to have an increased risk of death compared with OAT patients within the 'healthy' range.