 Most reviews conclude that opioids produce minimal impairment of human performance on tests of sensory, motor, or attentional abilities.However, recent studies have been able to show some impairments caused by morphine, which is not surprising, given that morphine is a central nervous system depressant.Morphine has resulted in impaired functioning on critical flicker frequency (a measure of overall CNS arousal) and impaired performance on the Maddox wing test (a measure of the deviation of the visual axes of the eyes).