High Doses of Opioids May Impair Driving

Pauline Anderson

January 17, 2013

Drivers taking 20 mg of morphine or more per day, or the equivalent, are up to 42% more likely to be involved in road trauma than drivers taking the lowest doses of opioids, according to a new study.

"Our findings have important implications in clinical practice and suggest that physicians may want to warn patients about potentially decreased driving ability when escalating to high opioid doses," the study authors, led by Tara Gomes, MHSc, Keenan Research Center of the Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, Canada, conclude.

"Furthermore, policy makers could improve public education surrounding the potential risks of opioid medications and could consider restricted drivers' licenses for patients treated with high-dose opioids," they write.

The study is published online January 14 in the JAMA Internal Medicine.

Daily Opioid Doses

The population based, case-control study included 5300 adults aged 18 to 64 years who were eligible for prescription drug coverage under the Ontario Provincial Public Drug Program, including the unemployed and disabled, and who were prescribed opioid analgesics from April 1, 2003, to March 31, 2011. It also included controls matched for sex, age, index year, emergency department visit for road trauma, and disease risk index, which researchers developed for all cases.

Investigators used various databases to identify claims for physician services, emergency department visits, and hospitalizations for injuries related to road trauma and for prescription medications dispensed to eligible residents. Opioids included in the study were oral formulations of codeine, morphine sulfate, oxycodone or hydromorphone hydrochloride, and transdermal fentanyl patches.

The researchers stratified the average daily dose of opioids into 5 categories of morphine equivalents (MEQs): very low ( < 20 MEQs), low (20 to 49 MEQs), moderate (50 to 99 MEQs), high (100 to 199 MEQs), and very high (200 MEQs or greater).

Of the 5300 participants in the study, 45.81% were drivers, 15.85% were passengers, and 10.92% were pedestrians; for 27.42%, the status was unknown or miscellaneous.

The researchers found no association between escalating opioid dose and odds of road trauma, with adjusted odds ratios ranging from 1.00 to 1.09 for each dose category compared with patients prescribed very low doses of opioids.

However, a subgroup analysis of drivers found that compared with patients prescribed very low opioid doses, those taking low and moderate doses had a 21% and 29% increased odds of road trauma, respectively. Patents prescribed high and very high doses of opioids had a 42% and 23% increased odds of road trauma compared with patients prescribed very low doses.

Table. Risk for Road Trauma in Drivers Taking Various Doses Opioids vs Very Low Doses

Opioid Dose Level Adjusted Odds Ratio (95% Confidence Interval)
Low 1.21 (1.02 - 1.42)
Moderate 1.29 (1.06 - 1.57)
High 1.42 (1.15 - 1.76)
Very high 1.23 (1.02 - 1.49)


The risk for road trauma in drivers taking very high doses of opioids was less than the risk in patients in the next highest dose category, possibly because "physiologic opioid tolerance among patients who undergo long term treatment at a fixed dose…may offset the detrimental effects of these drugs on driver performance," the authors write.

No association was seen between opioid dose and risk of road trauma among nondrivers. As well, risk for road trauma did not significantly differ between those who initiated opioid therapy in the prior 2 weeks and those with longer-term use.

The study population consisted of relatively young, socioeconomically disadvantaged residents of Ontario, and the findings may not apply to other populations. Another study limitation was that the authors couldn't determine how pain severity influenced the findings because the indication for opioid therapy was unknown. Further, there was no information on access to motor vehicles or the frequency of driving among patients, and the definition of road trauma has not been validated.

In an accompanying editorial, Mitchell H. Katz, MD, Los Angeles County Department of Health Services, California, said that prescribing physicians should ensure that patients understand the dangers of driving while taking opioids and should include the risk for road trauma when weighing the benefits and harms of these drugs.

"It is so tempting to prescribe and steadily increase the doses of opioids for our patients with chronic pain because we believe that we have no alternative treatments," Dr. Katz writes. "However, we must accept the limitations of our current chronic pain armamentarium and resist prescribing more opioids just because we believe that we have nothing better to offer. In the case of opioids for chronic pain, for the sake of our patients, less is often more."

This study was supported by a grant from the Ontario Ministry of Health and Long-term Care Drug Innovation Fund and the Institute for Clinical Evaluative Sciences, a nonprofit research institute sponsored by the Ontario Ministry of Health and Long-term Care. Ms. Gomes and Dr. Katz have disclosed no relevant financial relationships.

JAMA Intern Med. Published online January 14, 2013. Abstract Editorial