In the case of a Morphine overdose, where a hospital is concerned that the high dose of Morphine may be dangerous (depressing breathing and heartrate), they may administer
Naloxone (an opiate antagonist). The Naloxone finds its way to your opiate receptors and "competes" with Morphine for binding of the receptors. Because Naloxone has a higher affinity for the receptors than Morphine, the Naloxone will generally win out, replacing much of the Morphine at the receptor sites.