This chapter reviews the pharmacology of the intravenously administered opioids in the practice of geriatric anesthesiology. These drugs include morphine, meperidine, hydromorphone, fentanyl, sufentanil, and methadone. It is important that anesthesiologists understand the differences in pharmacology of opioids in elderly patients, in order to choose the appropriate drug and titrate precisely to achieve the desired analgesic effects while minimizing the risks of opioid toxicity. The key points for this chapter are as follows: (1) Elderly patients need about half the dose as younger patients, (2) The primary reason is pharmacodynamics (the elderly brain is more sensitive to opioids), (3) The pharmacokinetic changes with age are modest, (4) Studies in elderly animals show reduced numbers of μ receptors with increased age. That does not explain the reduction in dose, as decreased receptor density should decrease sensitivity to opioids. The enhancement in drug effect seen in the clinic is more likely attributable to changes in cyclonucleotide coupling and other downstream changes that occur in aging, and (5) Mepiridine should be used with caution in elderly patients due to its effects on myocardium, pharmacokinetics related to its metabolites, and its delirogenic properties.