"In 2011, 5,188 opioid-analgesic poisoning deaths also involved benzodiazepines (sedatives used to treat anxiety, insomnia, and seizures), up from 527 such deaths in 1999 (Figure 3). From 2006 through 2011, the number of opioid-analgesic poisoning deaths involving benzodiazepines increased 14% on average each year, while the number of opioid-analgesic poisoning deaths not involving benzodiazepines did not change significantly."
Chen, LH, Hedegaard, H, and Warner, M. Drug-poisoning deaths involving opioid analgesics: United States, 1999–2011. NCHS data brief, No. 166. Hyattsville, MD: National Center for Health Statistics, 2014.