Mortality due to drug overdose has risen consistently in the United States since the early 1990s, according to national statistics. But new research reveals that those numbers may not be accurate and deserve a closer look.

A study, “Defining Controlled Substances Overdose: Should Deaths from Substance use Disorders and Pharmaceutical Adverse Events be included?,” published in the current issue of Journal of Clinical Toxicology finds that the commonly used definitions are too broad, and include deaths that do not involve controlled substances while simultaneously underreporting deaths that do.

Researchers led by Nabarun Dasgupta, PhD, MPH, and his colleagues at the University of North Carolina at Chapel Hill and the North Carolina Department of Health and Human Services, examined all deaths in North Carolina between January 1, 2008 and December 31, 2011. They found that up to 16 percent of deaths considered “overdoses” by national authorities do not involve controlled substances.

The study suggests a new definition that includes deaths from substance use disorders, but not deaths due to severe side effects involving prescription medicines that are not controlled substances (pharmaceutical adverse events).

“There is considerable interest in the timely and accurate identification of deaths from controlled substances,” explained Dasgupta. “What we’ve found is that deaths from negative reactions to blood pressure medicine, for example, are being coded in the same way as deaths related to controlled substances like heroin or cocaine, and that the latter are being underreported. The underlying cause of these deaths is vastly different and the policy and behavioral changes needed to prevent them are distinct.”

“Our proposed definition would help garner more accurate estimates of the number of overdose deaths that involve illicit drugs and abusable prescription medicines. If you are evaluating an intervention that prevents drug abuse, you would not expect medication errors to decrease across the board,” Dasgupta continued.

This research has implications for evaluating the effectiveness of national measures to reduce overdose deaths, such as the Food and Drug Administration (FDA) Risk Evaluation and Mitigation Strategies (REMS) for long-acting and extended-release opioid analgesics. Since 1999, state and national statistics used to track drug-related deaths and inform policy decisions have relied on the World Health Organization’s International Classification of Disease 10th Revision (ICD-10). The paper will assist authorities in creating more accurate definitions for overdose in future revisions for ICD.