Chronic pain, defined as continuous pain that lasts for more than 3 months, has a great impact on the patient’s everyday life and quality of life. Approximately 20% of the world’s population suffers from chronic pain, therefore chronic paint treatment should be given close attention. Morphine, a medicine used in the treatment of pain, has been used since ancient times. Its usage arouses many controversies, nonetheless it is still used. Morphine is one of the most commonly used drugs in chronic pain treatment. Its analgesic effect is achieved through morphine-6-glucuronide active metabolite. Morphine is used orally, subcutaneously, intravenously, intramuscularly, intrathecally and rectally. For each mode of administration, due to many side effects, it is necessary to know effective and safe doses of morphine. Some of the side effects are respiratory depression, nausea and vomiting, constipation, urine retention, pruritus etc. The cause of the side effects is considered another metabolite, morphine-3-glucuronide. According to the guidelines, morphine treatment should be introduced gradually in smaller does and closely monitored for the duration of the treatment. This reduces potential side effects. In case of addiction or substance abuse, the treatment should be terminated.