The Impact of Opioid Prescriptions on Duration of Disability

This study examines the effect of opioid prescriptions on the duration of temporary disability benefits among workers with work-related low back pain cases. While medical practice guidelines often advise against routine (i.e., nonsurgical) use of opioids for treatment of low back injuries (See American College of Occupational and Environmental Medicine (ACOEM), 2008; Bigos, et al., 1994; Chou, et al., 2007), opioid use in nonsurgical lower back cases is common (See Adams et al., 2001; Reid et al., 2002).

Prior studies have established empirical associations between opioid prescribing and claim outcomes, with many studies finding longer duration of temporary disability benefits when workers had opioid prescriptions. However, these studies did not establish a causal link between opioid prescriptions and outcomes. Other factors, such as unobserved injury severity or worker characteristics unrelated to injury severity may be related both to opioid prescribing and the duration of temporary disability benefits, in which case the measured relationship between opioid prescriptions and duration may not reflect an effect of opioids.

The main contribution of this present study is the use of empirical models designed to estimate the causal effect of opioid prescriptions on the duration of disability. We use local area variation in opioid prescriptions to construct instrumental variables for whether a given injured worker was given opioid prescriptions. The idea behind this approach is that local prescribing patterns may influence whether an injured worker will have a prescription for opioids. Indeed we show that workers who live in areas where physicians are more likely to prescribe opioids were more likely to receive and fill opioid prescriptions, suggesting that physicians play a role in opioid prescribing rates. A 10 percentage point increase in the local rate of prescribing at least three opioid prescriptions led to a 3.1 percentage point higher likelihood that an otherwise similar injured worker would receive at least three opioid prescriptions. At the same time, these prescribing patterns are likely to be exogenous with respect to unobserved workers’ characteristics.

We found that more extensive opioid prescribing led to longer duration of temporary disability. When we compared the effect of three or more opioid prescriptions versus no prescriptions, opioids led to 42 percent longer duration of temporary disability. When we compared the effect of longer-term opioid prescriptions to no opioid prescriptions, the effect was to more than double the duration of temporary disability benefits. In contrast to these results for more extensive opioid prescribing, we found little evidence of longer temporary disability benefits when measures of opioid prescribing include claims with one or two opioid prescriptions.