According to the World Health Organization (WHO) guidelines, oral morphine is the first choice drug for treating moderate to severe cancer-related pain. The fear of the side effects caused by this drug and the scarce information about prevention and management of these effects are the main reasons for the underuse of morphine. The aim of this paper is to provide a review of the literature on the side effects most frequently present both in the titration phase and during chronic administration of oral morphine and to describe the appropriate treatment.