(Boston)--With opioid addiction and prescription drug abuse considered one of the biggest public health threats of our time in the U.S., many are asking why so many Americans are struggling with addiction to illegal drugs and prescription medications. New research suggests that chronic pain may be part of the answer.

In a study that appears in the May issue of the Journal of General Internal Medicine, researchers at Boston University School of Medicine and Boston Medical Center have found that the majority of patients misusing drugs and alcohol have chronic pain and many are using these substances to "self-medicate" their pain.

According to the researchers, many illegal drugs such as marijuana and heroin have pain-relieving properties. The researchers screened approximately 25,000 patients in primary care for illegal drug use and misuse of prescription medications. Among these patients, 589 who screened positive for substance use were asked questions about chronic pain and their substance use. Substance use was defined as use of illegal drugs (heroin, marijuana, cocaine, etc.), use of prescription drugs in ways other than prescribed or high risk alcohol use.

They found that 87 percent of those who screened positive for illegal drug use, misuse of prescription drugs or heavy alcohol use suffered from chronic pain. Half of these patients graded the pain as severe. In the subgroup that was using illegal drugs, 51 percent reported using one or more drug specifically to alleviate physical pain. In those using prescription drugs without a prescription or using more than prescribed, 81 percent identified self-medication of pain as the reason for misuse. With regard to high risk alcohol use, the majority (79 percent) did so to manage pain.

"While the association between chronic pain and drug addiction has been observed in prior studies, this study goes one step further to quantify how many of these patients are using these substances specifically to treat chronic pain. It also measures the prevalence of chronic pain in patients who screen positive for illegal drug use and prescription drug abuse," explained corresponding author Daniel Alford, MD, MPH, associate professor of medicine and assistant dean of Continuing Medical Education and director of the Safe and Competent Opioid Prescribing Education (SCOPE of Pain) program at BUSM. He is also the director of BMC's Clinical Addiction Research and Education Unit.

The results of this study suggest that counseling focused only on informing patients about the negative consequences of drug and alcohol use may miss a key aspect of why people are using these substances. "Pain should be treated as part of the long-term strategy for recovery. If drugs are being used to self-medicate pain, patients may be reluctant to decrease, stop, or remain abstinent if their pain symptoms are not adequately managed with other treatments including non-medication-based treatments," added Alford.

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This research was part of the ASPIRE study, which was funded by the National Institute on Drug Abuse (RO1 DA025068) and the Massachusetts Department of Public Health both of which received funding from the Center for Substance Abuse Treatment (TI018311). Other support included the National Center for Research Resources (UL1RR025771).