The clinical benefit and increased application of opioid rotation has focused attention on efficacy differences between opioids and their respective equianalgesic dose ratios. Understanding the differences between the opioids is critical to understanding their equianalgesic dose ratios and for adjusting therapy following rotation to a new analgesic. The purpose of this article is to describe controversies regarding the relative potencies of these agents as presented in current equianalgesic charts and to provide pharmacologic information to assist the clinician with opioid rotation.