Effect of codeine and oxazepam on afternoon cortisol secretion in men

The objective of this study was to investigate the effects of oral codeine and oxazepam on afternoon cortisol secretion. Nine subjects received either oxazepam (30 mg) or codeine (30 mg) or placebo at 1700h on separate days in a counterbalanced design; the subjects were not aware of the sequence. Blood samples were collected with an indwelling intravenous catheter at 30-min intervals from 1500h to 1630h. Codeine, but not oxazepam, suppressed cortisol secretion. The trend of the declining cortisol values following codeine was significantly linear. These results are consistent with other evidence indicating the presence of an inhibitory opioid mechanism in the human hypothalamo-pituitary-adrenal (HPA) axis. The cortisol response to codeine may be a reliable and potentially useful paradigm for the study of the role of opioidergic mechanisms in HPA axis dysfunction.