Taking opioids for the treatment of pain has been associated with increased risks of crashing among drivers, but it is unknown whether this applies to all opioids or pertains to specific opioids only. A new British Journal of Clinical Pharmacology study found that the influence of single analgesic doses of methadone and buprenorphine -- two different opioids -- on driving performance was mild and below the impairment threshold of a blood alcohol concentration of 0.5 mg ml-1.

Both opioids produced impairments of cognitive task performance and increased sleepiness at the highest dose, however. Four out of the 22 participants in the study stopped their on-road driving test while under the influence of either opioid due to sleepiness.

The findings indicate that it is impossible to state that use of buprenorphine and methadone will not impair driving in any patient. Consequently, patients should always be informed about the potential driving impairment that might be caused by buprenorphine and methadone.

"For the first time an actual on-road driving study has been performed to investigate the acute effects of opioids in drug-naïve persons on driving. The results tell us that caution is required when initiating treatment with these drugs," said lead author Dr. Maren Cecilie Strand, of Oslo University Hospital, in Norway.