Many studies have reported lower opioid dose requirements for older adults in the immediate postoperative period. While there is great variability between patients in opioid doses required for effective analgesia, in general older adults need lower opioid doses (compared to the usual adult doses) to achieve equivalent analgesia. Age-related physiological changes do not fully explain this observation. Although more rapid accumulation of active opioid metabolites may result from reduced renal function in the elderly, the major factor contributing to the reduced dose requirements in the elderly is an increase in brain sensitivity to the effects of opioids, both the analgesic effects and the adverse effects such as nausea and respiratory depression. It is common practice to start with 25% to 50% of the usual adult dose, and titrate according to response.