Opioid substitution treatment (OST) to reduce mortality

Opioid substitution treatment (OST)/Opioid Agonist Treatment (OAT) was found to be effective in several systematic reviews (Mattick et al., 2009, Mathers et al., 2013, Sordo et al., 2017, Santo et al. 2021) in reducing the risk of death.

Sordo et al., (2017) conducted a systematic review and meta-analysis of cohort studies (19 eligible cohorts, following 122 885 people treated with methadone over 1.3-13.9 years and 15 831 people treated with buprenorphine over 1.1-4.5 years) and found:

• all cause mortality rates were 11.3 and 36.1 per 1000 person years in and out of methadone treatment (unadjusted out-to-in rate ratio 3.20, 95% confidence interval 2.65 to 3.86) and reduced to 4.3 and 9.5 in and out of buprenorphine treatment (2.20, 1.34 to 3.61)
• In pooled trend analysis, all cause mortality dropped sharply over the first four weeks of methadone treatment and decreased gradually two weeks after leaving treatment.
• All cause mortality remained stable during induction and remaining time on buprenorphine treatment. Overdose mortality evolved similarly, with pooled overdose mortality rates of 2.6 and 12.7 per 1000 person years in and out of methadone treatment (unadjusted out-to-in rate ratio 4.80, 2.90 to 7.96) and 1.4 and 4.6 in and out of buprenorphine treatment.

Santo et al., (2021) analysed both observational studies ( 36 studies, N= 749 634) that collected data on all-cause or cause-specific mortality among people with opioid dependence while receiving and not receiving OAT as well as randomized clinical trials (15 RCTs, N = 3852). Results found that:

• the rate of all-cause mortality during OAT was more than half of the rate seen during time out of OAT (RR, 0.47; 95% CI, 0.42-0.53). This association was consistent regardless of patient sex, age, geographic location, HIV status, and hepatitis C virus status and whether drugs were taken through injection. Associations were not different for methadone (RR, 0.47; 95% CI, 0.41-0.54) vs buprenorphine (RR, 0.34; 95% CI, 0.26-0.45). 
• There was lower risk of suicide (RR, 0.48; 95% CI, 0.37-0.61), cancer (RR, 0.72; 95% CI, 0.52-0.98), drug-related (RR, 0.41; 95% CI, 0.33-0.52), alcohol-related (RR, 0.59; 95% CI, 0.49-0.72), and cardiovascular-related (RR, 0.69; 95% CI, 0.60-0.79) mortality during OAT. 
• In the first 4 weeks of methadone treatment, rates of all-cause mortality and drug-related poisoning were almost double the rates during the remainder of OAT (RR, 2.01; 95% CI, 1.55- 5.09) but not for buprenorphine (RR, 0.58; 95% CI, 0.18-1.85).
• All-cause mortality was 6 times higher in the 4 weeks after OAT cessation (RR, 6.01; 95% CI, 4.32-8.36), remaining double the rate for the remainder of time not receiving OAT (RR, 1.81; 95% CI, 1.50-2.18).
• Opioid agonist treatment was associated with a lower risk of mortality during incarceration (RR, 0.06; 95% CI, 0.01-0.46) and after release from incarceration (RR, 0.09; 95% CI, 0.02-0.56)