In a study that compared payer groups, a questionnaire elicited reasons for nonadherence . Similar reasons for nonadherence emerged including financial, fear of addiction or increased medication use, and running out medication.
Only 1 study used CAGE (Cut down, Annoyed, Guilty, and Eye-opener), an alcohol-screening questionnaire, to determine a possible relationship with analgesic adherence. In this study, there were 19 cases of opioid deviation, 16% of which were CAGE positive and had severe deviation toward less than the prescribed doses . In further analysis, no association was found between CAGE positively and opioid deviation to higher intake . Two other studies gathered data on history of depression, substance use, and alcohol use but no significant correlation was found [3,13].
Previous literature has reported overall analgesic adherence rates among oncology patients ranging from 62% to 72% . Factors at the provider and system level have been considered in past research, but the patient perspective is poorly represented in the literature . A majority of studies on analgesic adherence have been completed with cohorts made up predominantly of white individuals [13,23,24], while others focus on racially homogenous and/or ethnically different populations in other countries [21,25,26].
This review confirms that there is a paucity of well-designed studies that describe the associations between racial and ethnic disparities and adherence to opioids among patients with cancer pain. This is despite the fact that moderate to severe cancer pain in the U.S. is managed mainly with analgesics and specifically with opioids . In addition, cancer patients with health insurance have both more pharmacy claims as well as more claims for higher doses of opioids  compared to noncancer patients. The lack of attention to analgesic and opioid adherence among cancer patients is surprising in the light of the recent high-profile initiatives to reduce opioid misuse .
Multiple studies highlighted the importance of pain management education and adequate pain assessment for effective analgesic use [4,16]. In the study in the palliative care setting, the authors concluded that patients who are educated, counseled, and monitored by a palliative or supportive care team have less episodes of opioid deviation and trends toward lower opioid use . A systematic review and meta-analysis confirmed findings that educational interventions for patients improved knowledge about cancer pain management, however, most did not improve reported adherence to analgesics [27,28]. These findings emphasize the need for further research on interventions to improve racial/ethnic disparities in analgesic adherence for cancer pain.
The findings of this review should be evaluated in the context of the following limitations. First, adherence to a prescribed regimen is a difficult outcome to measure and a majority of studies in this review used subjective measures to assess analgesic adherence for cancer pain. Of note, self-report was the primary measurement employed. Studies in non–cancer pain settings that have evaluated various methodological approaches to adherence measurement found that patients are likely to over-report adherence when using self-report or a diary format in comparison to an electronic monitoring system. Only 1 study in this review used an objective measure of adherence . Some previous studies contend that self-report in comparison to other, objective measurements of medication adherence are accurate . Further research is needed to determine the most accurate measurement of analgesic adherence in cancer patients.