When given in single doses to healthy volunteers, opioid analgesics im
pair reaction time, muscle coordination, attention, and short-term mem
ory sufficiently to affect driving and other skilled activities. Despi
te the increasing use of oral morphine daily, little is known about th
e effect of long-term opioid therapy on psychomotor performance. To ex
amine the effects of continuous morphine medication, psychological and
neurological tests originally designed for professional motor vehicle
drivers were conducted in two groups of cancer patients who were simi
lar apart from experience of pain, 24 were on continuous morphine (mea
n 209 mg oral morphine daily) for cancer pain; and 25 were pain-free w
ithout regular analgesics. Though the results were a little worse in t
he patients taking morphine, there were no significant differences bet
ween the groups in intelligence, vigilance. concentration, fluency of
motor reactions, or division of attention. Of the neural function test
s, reaction times (auditory, visual, associative), thermal discriminat
ion, and body sway with eyes open were similar in the two groups; only
balancing ability with closed eyes was worse in the morphine group. T
hese results indicate that, in cancer patients receiving long-term mor
phine treatment with stable doses, morphine has only a slight and sele
ctive effect on functions related to driving.