Opioids are the most effective analgesics for cancer pain treatments. But the ineffective treatment of cancer pain is often related to insufficient knowledge of opioids and fear of the addiction along with the side effects. To achieve effective treatment of cancer pain with opioids, we need a careful assessment of pain, proper use of opioids and regular review of the effectiveness of prescribed opioids. Basic principles of opioids therapy in cancer pain are ① Oral opioids (or transdermal) if possible; ② Combination of long-acting opioids for constant pain with short-acting opioids for breakthrough pain; ③ "Opioids rotation"in poor analgesia and significant side effects with the calculations of the morphine equivalent daily dose (MEDD) ④ Initiation of prophylactic treatment for constipation and nausea. In this review, I will describe the essential aspects of opioids therapy, pharmacology, rotation, properties of the individual opioids, and management of common side effects.