Opioid use is often assessed in studies by participant self-report via a drug use diary or by urine drug testing. Opioid use as a health outcome can be defined in a variety of ways, including as a yes/no outcome or as a total count of instances of drug use over a defined period of time. 

Individuals taking buprenorphine have less opioid use compared to individuals taking a placebo or no medication at all. In a Cochrane Review of 31 studies, participants taking buprenorphine had about 1.1 fewer positive urine drug tests per study period than participants taking no medication at all, with higher daily buprenorphine doses associated with less opioid use. 

Opioid overdose events and mortality are typically assessed using mortality data from government health records or healthcare visit data from hospital electronic health records and insurance claims databases. 

Compared to taking no medications for opioid use disorder, taking either buprenorphine or methadone is associated with lower odds of opioid-related overdose. In a large national study, opioid-related overdoses over three months were reduced by 76% among people taking either buprenorphine or methadone compared to no medication at all. In a study of Massachusetts data, buprenorphine treatment was associated with a 38% reduction in opioid-related mortality over 12 months compared to no medications.

Treatment retention is defined as how long individuals stay in treatment and is typically measured by attendance at outpatient appointments. Studies can also define treatment retention as the number of weeks that individuals fill a prescription for buprenorphine. Most studies focus on treatment retention in the timeframe of three months, six months, or one year. 

Because of the various ways that treatment retention can be defined and measured, estimates of the effect of buprenorphine on treatment retention can be highly variable. In a recent meta-analysis of 10 randomized trials and 3 observational studies, treatment retention for buprenorphine ranged from 20.2% to 78.3%. A systematic analysis of studies assessing various buprenorphine prescribing characteristics found that higher daily buprenorphine doses were associated with higher rates of treatment retention, as was initiating buprenorphine during a hospitalization or incarceration.