"There is some evidence that higher prescribed doses increase the risk of drug overdose among individuals treated with opioids for chronic non-cancer pain.4 Specifically, the risk of drug-related adverse events is higher among individuals prescribed opioids at doses equal to 50 mg/d or more of morphine. The association of opioid prescribing patterns with risk of over-dose may vary across groups of patients; opioid treatment recommendations for pain are typically specific to particular subgroups such as those with chronic noncancer pain,5 cancer-related pain, and substance use disorders.6 However, potential subgroup differences in opioid prescribing have not been examined."

Source

Bohnert, Amy S.B., et al., "Association Between Opioid Prescribing Patterns and Opioid Overdose-Related Deaths," Journal of the American Medical Association, April 6, 2011, Vol 305, No. 13, p. 1315.
http://jama.jamanetwork.com/a…