The cognitive and psychomotor effects of morphine in healthy subjects: a randomized controlled trial of repeated (four) oral doses of dextropropoxyphene, morphine, lorazepam and placebo

Ten healthy subjects (four male) of mean age 31 years (range 25-40) took pa rt in a randomized double-blind four-way crossover study to examine the cog nitive and psychomotor effects of repeated oral doses of dextropropoxyphene and morphine. Four treatments were compared: dextropropoxyphene napsylate 100 mg, morphine sulphate 10 mg, lorazepam 0.5 mg and placebo. Four doses o f each drug were given at 4-h intervals to each subject on four separate st udy days at least 1 week apart. Cognitive function was assessed using choic e reaction time, number vigilance, memory scanning, immediate and delayed w ord recall, word recognition, picture recognition, critical flicker fusion threshold (CFFT) and subjective measures of alertness, calmness and content ment. Lorazepam impaired the speed of responding on all tasks in which spee d was recorded (except digit vigilance) and increased subjective ratings of calmness. Morphine had one major effect, which was to increase the accurac y of responding on the choice reaction time task, at every assessment. Morp hine produced some sporadic effects in other tests and an increase in subje ctive calmness. Dextropropoxyphene impaired performance on choice reaction time and picture recognition. These data show that oral morphine may enhanc e performance in some measures of cognitive function, whereas dextropropoxy phene (in usual therapeutic doses) seems more likely to cause impairment. N either opioid has substantial effects on cognition and psychomotor function compared with lorazepam. (C) 2000 international Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved.