"Opioids were frequently implicated in overdose deaths involving other pharmaceuticals. They were involved in the majority of deaths involving benzodiazepines (77.2%), antiepileptic and antiparkinsonism drugs (65.5%), antipsychotic and neuroleptic drugs (58.0%), antidepressants (57.6%), other analgesics, antipyretics, and antirheumatics (56.5%), and other psychotropic drugs (54.2%). Among overdose deaths due to psychotherapeutic and central nervous system pharmaceuticals, the proportion involving only a single class of such drugs was highest for opioids (4903/16 651; 29.4%) and lowest for benzodiazepines (239/6497; 3.7%)."
Christopher M. Jones, PharmD, Karin A. Mack, PhD, and Leonard J. Paulozzi, MD, "Pharmaceutical Overdose Deaths, United States, 2010," Journal of the American Medical Association, February 20, 2013, Vol 309, No. 7, p. 658.