AMSTERDAM - Unraveling the factors fueling America's opioid epidemic remains complicated.
The increasing number of deaths from drug use in the United States has been linked with a surge in the distribution of prescription painkillers as one factor. A new study suggests that some other overlooked factors might be contributors, as well.
In counties across the United States, when incarceration rates rise and household incomes fall, drug-related deaths increase, according to a study published Wednesday in the medical journal Lancet Public Health.
The study found that, from 1983 to 2014, when there was a large decrease in average household income -- a drop of nearly a third -- there was an associated 12.8% increase in drug-related deaths in the county.
Average increases of 7,018 jail admissions per 100,000 people and 255 prison admissions per 100,000 people were associated with a 1.5% and a 2.6% increase in the county's death rate from drug use, respectively, the study found.
"We know that most incarceration is only very loosely related to the crime rate," said Lawrence King, a professor of economics at the University of Massachusetts Amherst, who was the senior author on the study.
"If we're incarcerating people because we don't like the negative effects of drugs, what this study shows is it's counterproductive," King said.
"It's a strong argument for medicalization of hard drugs as opposed to criminalization, which actually makes a lot of sense, given that the definition that we use of addiction is the continued obsessive-compulsive use of drugs despite negative consequences," he said. "So imprisoning people -- giving them negative consequences to get them to stop using drugs -- is not going to work by the very definition we're using of addiction."
In total, the new study included data for 2,640 counties in the United States between 1983 and 2014. Separate research previously has shown that drug-related deaths across counties between 1980 and 2014 climbed overall by more than 600%.
The study involved analyzing mortality data from the US National Vital Statistics System and Institute for Health Metrics and Evaluation, household income data from the US Census Bureau, and incarceration data by county from the Vera Institute of Justice.
As an additional variable, the researchers obtained county-level data on retail opioid prescription rates between 2006 and 2014 from the CDC. They found that the incarceration rates were significantly associated with overdose deaths even after controlling for local opioid prescription rates since 2006.
On average, 130 people in the United States die every day from an opioid overdose, according to the CDC.
"I think the most surprising thing was that the prescriptions of the opioids do not seem to be the major cause of the opioid crisis. It's contributing for sure but ... once we put in our controls, it had no predictive power," King said.
Typically, "the national dialogue on opioid addiction is all focused on the behavior of the pharmaceutical companies -- and I don't think they should be left off the hook -- but it's all focused on the supply and no focus on the demand," he said, adding that one limitation of the new study is that the prescription data only dated back to 2006.
"They really started to prescribe opioids a lot from '95. So there could have been a big effect earlier on and then that carried forward," he said. "So we can't conclusively say they have no effect, and I don't believe they have no effect."
The study had some other limitations, including that the findings only suggest an association between reduced household incomes, high incarceration rates and drug-related deaths. More research is needed to determine whether a causal relationship exists between those factors, and to explain why the complex associations exist.
The new study demonstrates the "powerful potential" that better understanding of incarceration could have on public health, James LePage, chief of research at the Department of Veterans Affairs' VA North Texas Health Care System in Dallas, wrote in a commentary paper that published alongside the study on Wednesday.
"The impact of incarceration on individuals and families can be devastating leading to an increased incidence of homelessness, unemployment, divorce, and recidivism. Individuals who have been incarcerated are more likely to be substance users and have a higher risk of premature death," LePage wrote in the commentary.
"Economic deprivation is also a known risk factor for substance abuse and early death. It seems plausible, therefore, that both rates of incarceration and impoverishment might contribute to changes in mortality from drug use," he wrote. "The results highlight the need to evaluate current approaches towards the issues associated with incarceration."
CNN's Ben Tinker contributed to this report.
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