Opioid painkillers more common in low-income households

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Household income may determine whether a patient uses an opioid or nonopioid analgesic for dental pain, a new study has found. Participants from households making less than $15,000 per year were nearly twice as likely to take opioids than those from the highest income bracket.

Using survey data from nearly 14,000 participants in Canada, researchers analyzed how likely respondents were to take different forms of analgesics. Their study findings and analysis were published in PLOS One (May 1, 2017).

"Our findings suggest that policies designed to improve access to dental services for those who are most socially and economically marginalized may, in part, assuage the need for opioid analgesics," wrote the authors, led by Jamie Moeller, a student researcher and fourth-year dental student at the University of Toronto.

Pain relief determined by income?

Like the U.S., Canada is facing an opioid epidemic, with rising rates of opioid addiction, abuse, and fatalities. As policymakers figure out how to best address this public health crisis, they rely on research that assesses potential causes and correlations. Moeller and colleagues, therefore, studied analgesic use and toothaches, hoping to identify socioeconomic factors that influence whether someone takes opioids for dental pain.

“Policies designed to improve access to dental services for those who are most socially and economically marginalized may, in part, assuage the need for opioid analgesics.”
— Jamie Moeller and colleagues

For their analysis, the researchers used data from the 2003 Canadian Community Health Survey (CCHS), which asked a geographically representative sample of Canadians for demographic, socioeconomic, health status, and health behaviors information. Although the data were somewhat dated, the researchers chose the survey because it asked respondents specifically about dental pain, dental visits, and analgesic use. The survey also represented about 98% of the population of the province of British Columbia at the time.

Almost 14,000 respondents age 20 and older were included in the analysis. Of those, 10% experienced a toothache in the past month, and 77% took some form of analgesic, although not necessarily for the tooth pain.

Those who experienced toothaches and frequent dental pain in the past month were significantly more likely to use analgesics of any kind, the researchers found. However, the type of analgesic used varied significantly by participants' household income.

Odds of participants with toothache taking an analgesic by annual household income
Household income per year Odds of taking a nonopioid analgesic* Odds of taking an opioid analgesic*
$15,000 or less 53% less likely 97% more likely
$15,000 to $29,999 62% less likely 36% more likely
$30,000 to $49,999 28% less likely 51% more likely
Data displayed are before researchers adjusted for confounding variables.
*Compared with participants with an annual household income of $80,000 or more per year.

Study participants with toothaches from higher-income households reported using nonopioid analgesics significantly more often than those from lower-income households. Conversely, they used opioids significantly less often than their lower-income peers.

"This division exists for those who did not report a toothache in the past month but becomes more pronounced in the presence of a recent toothache," the authors wrote. "This observation may be suggestive of an unequal distribution in the severity of tooth pain; those with less income may experience more severe forms of dental pain that is not alleviated by conventional painkillers, such as Tylenol, and, accordingly, require prescribed opioids for appropriate pain relief."

The authors added that the correlation between painkiller preference and household income also may be influenced by Canada's healthcare system, which finances prescription drugs for those who qualify but not over-the-counter medications.

"As a result, those with less income may be forced to take existing prescription analgesics, intended for the relief of other forms of pain (namely, opioids such as codeine or oxycodone) rather than safer but more expensive analgesics, such as Tylenol or ibuprofen," the authors wrote.

Parsing the findings

The authors believed this was the first study to associate opioid prescriptions for people who experienced recent tooth pain with household income. However, they also noted that, while the income gradients for nonopioid users were significant before and after they adjusted for confounding variables, the income differences were not statistically significant for opioids after adjusting for confounding variables. The findings are still relevant, though, they stated.

"Notably, after adjusting for potential confounders -- namely age, sex, mental health indicators, and pain-related comorbidities -- the income effect from our unadjusted model disappears," the authors wrote. "Although these results appear to indicate that the control variables are indeed confounders, we hesitate to accept this interpretation for two reasons."

Moeller and colleagues argued that two of the variables, poor mental health and chronic pain, may be mediators that lead to prescription opioid use more than confounding variables. They also pointed out that their model was based on all confounding variables being equal, but they do not believe that all the control variables are equal, and that evidence shows the types, frequencies, and prevalence of diseases vary between socioeconomic groups.

Other study shortcomings include using older data that may not be entirely representative of Canada's present demographics. They also can't be certain whether the analgesic use was specifically for tooth pain.

Nevertheless, the authors found a surprising correlation between analgesic preference and household income that warrants further study. Moeller and colleagues emphasized that expanding dental care to the poor may help curb the opioid epidemic.

"Expanding and improving dental care programs that benefit the poor, and applying policy approaches that focus on the social determinants of health, may help reduce the use of prescription opioids," they concluded. "Such efforts may ultimately help to narrow differences in health between the rich and the poor, providing social and economic benefits to the broader population."

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