Magnesium oxide for constipation
Goal: What trials of magnesium oxide used in adults with chronic constipation, and how many improved.
Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.
Updated 10 Nov 2026- Dose
1.5 g of magnesium oxide a day in a trial of 90 adults.[1]
- Form
Magnesium oxide, an osmotic laxative.[2]
- How long
28 days.[1]
- What studies found
In 2 trials pooled in a 2023 review, 68% improved on magnesium oxide against 19% in the control groups, with 3.72 more bowel movements a week.[3] In the 2021 trial, 68.3% improved, against 69.2% with senna and 11.7% with placebo.[1] A 2023 US guideline gives magnesium oxide a conditional recommendation.[2]
Ask a doctor first
Laxative doses of magnesium can be well above the US upper limit of 350 mg a day, but part of the magnesium is not absorbed.[4] Very large doses of magnesium laxatives, usually above 5,000 mg a day, have caused magnesium toxicity, and kidney disease raises the risk.[4]
People with kidney disease, or who take a medicine every day, should ask a doctor or pharmacist first.[4]
References
- Senna Versus Magnesium Oxide for the Treatment of Chronic Constipation: A Randomized, Placebo-Controlled Trial. Morishita D, Tomita T, Mori S, Kimura T, Oshima T, Fukui H, et al. Am J Gastroenterol, 2021. PMID 32969946
- American Gastroenterological Association-American College of Gastroenterology Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation. Chang L, Chey WD, Imdad A, Almario CV, Bharucha AE, Diem S, et al. Gastroenterology, 2023. PMID 37211380
- The effect of food, vitamin, or mineral supplements on chronic constipation in adults: A systematic review and meta-analysis of randomized controlled trials. van der Schoot A, Creedon A, Whelan K, Dimidi E Neurogastroenterol Motil, 2023. PMID 37243443
- Magnesium: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov