Assessment of the Analgesic Effect of Magnesium and Morphine in Combination in Patients With Cancer Pain: A Comparative Randomized Double-Blind Study

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Morphine is the first-choice drug for moderate-to-severe cancer pain, nevertheless, some patients do not achieve adequate pain relief or exhibit intolerable side effects. The purpose of this study was to establish whether the analgesic effect of morphine improves in patients with cancer when administered in combination with magnesium.


Randomized double-blind study was conducted with 40 patients older than 18 years with cancer pain using morphine. Group 1 (G1) patients were given magnesium sulfate (65 mg elemental magnesium) twice per day by the oral route. Group 2 (G2) patients were given placebo twice per day. All the patients were administered morphine as needed. They were also given acetaminophen at 2 to 3 g/d. Adjuvants could be used when indicated. The following variables were assessed: pain intensity on a numeric scale at baseline and at weeks 1, 2, 3, and 4; functional performance and quality of life at baseline and week 4; and dose of morphine used.


No difference was found between the groups as to pain intensity, dose of morphine used, functional performance, quality of life, or side effects. The average daily dose of morphine increased gradually, being significant in G2.


The use of morphine combined with elemental magnesium at a dose of 65 mg twice per day by patients with cancer did not induce a better analgesic effect, did not improve their functional performance or quality of life, and did not reduce the occurrence of side effects. The dose of morphine increased significantly in G2.

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