Efficacy of Magnesium Supplementation in Functional Constipation: A Systematic Review

Magnesium supplementation has been proposed as a therapeutic option for functional constipation due to its osmotic properties, role in smooth muscle contraction, and influence on aquaporin-3 expression; however, the evidence has not been systematically synthesized.This review assessed whether magnesium supplementation, in any formulation, improves stool frequency, stool consistency, or quality of life in patients of any age with functional constipation, compared with placebo, standard care, or an active comparator.A systematic search of PubMed, Scopus, Web of Science, EMBASE, and CINAHL was conducted over a 10-year period to December 2025.Study quality was assessed utilizing the Mixed Methods Appraisal Tool.Due to substantial heterogeneity in the studies, a narrative synthesis was performed.This review was reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement.The certainty of the evidence was not formally graded.Seven studies (n = 690) met the inclusion criteria, addressing functional constipation across infant, pediatric, and adult populations.Five were randomized controlled trials, and two were nonrandomized studies.Four of seven studies showed statistically significant between-group improvements in stool frequency.Six studies reported stool consistency numerically, with statistically significant between-group differences in four; the remaining studies showed either within-group improvement or no significant differences between groups.Constipation-specific quality-of-life testing was assessed using a validated instrument in only two studies, both of which showed significant between-group improvement.Magnesium oxide was the most commonly used formulation in adults.No serious adverse events were reported in any trial, although adverse event reporting was inconsistent across studies.The findings suggest that magnesium supplementation, primarily magnesium oxide, may improve outcomes in functional constipation, but are not sufficient to support a treatment recommendation.The findings relate to magnesium oxide and cannot be assumed to apply to other forms of magnesium supplementation.The evidence base is limited by small sample sizes, heterogeneous study designs, and confounded interventions.Double-blind, placebo-controlled trials with standardized outcomes are needed to further explore this domain.