Abstract
Objectives. A recent US federal review and clinical guideline on opioids for chronic pain asserted that the literature contributes no evidence on efficacy because all trials had "inadequate duration." To explore the evidence, we examined durations of studies on opioid, nonopioid drug, and behavioral therapies for chronic pain.
Methods. We retrieved Cochrane reviews of anti-convulsants, antidepressants, NSAIDs, opioids, or behavioral interventions for chronic pain. We also examined all opioid treatment studies retrieved for the federal evidence report but excluded due to "inadequate duration."
Results. Of 378 Cochrane reviews retrieved, 72 evaluated one of the five therapies. Six of these 72 were excluded because they were proposals without data or investigated acute pain. Fourteen addressed multiple interventions, leaving 52 for analysis. We graphed numbers of trials vs duration for the five treatments reviewed in the Cochrane Library, compared with durations of opioid trials dropped from the federal evidence report. Most graphs were over-dispersed Poisson distributions. Nearly all trials had active treatment durations of 12 weeks or less.
Conclusions. No common nonopioid treatment for chronic pain has been studied in aggregate over longer intervals of active treatment than opioids. To dismiss trials as "inadequate" if their observation period is a year or less is inconsistent with current regulatory standards. The literature on major drug and nondrug treatments for chronic pain reveals similarly shaped distributions across modalities. Considering only duration of active treatment in efficacy or effectiveness trials, published evidence is no stronger for any major drug category or behavioral therapy than for opioids.