The aim of this study was to assess the analgesic, bleeding and nausea/vomiting effects of magnesium with and without metamizol on post-tonsillectomy patients. This prospective and randomised clinical trial included 54 patients aged 18-63 years who were scheduled for elective tonsillectomy. The patients were randomly divided into two groups and administered either magnesium with metamizol or only metamizol. They had been classified as physical status class I and II using the American Society of Anesthesiologists guidelines. All patients underwent the same surgical procedure performed by a single surgeon. The groups did not differ according to age, sex, or duration of anaesthesia or surgery. Postoperative pain, bleeding and nausea/vomiting were evaluated using the VAS and bleeding and nausea/vomiting scores on the first, fifth and tenth days. On the first, fifth and tenth postoperative days, the VAS scores of the magnesium with metamizol group were significantly lower than those of the metamizol-only group (p1 = 0.001; p5 = 0.015; p10 = 0.015). There were no significant differences in postoperative bleeding and nausea/vomiting scores between the two groups (p = 0.425 and p = 0.258, respectively). This study showed that magnesium enhanced the analgesic effect on post-tonsillectomy pain. Use of magnesium with an analgesic drug may be beneficial for management of post-tonsillectomy pain.