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ingestible · for constipation

Magnesium Citrate

Reviewed by the Nimbera editorial team · Last updated May 2026

Kubota et al. double-blind RCT (n=children with functional chronic constipation, magnesium oxide 30 mg/kg/day) found significant improvements in defecation frequency and stool consistency vs placebo at 4 weeks (p<0.05). Review-level evidence rates magnesium compounds Level I evidence, Grade B for constipation. PMID 31952280.$15-$30 for powder supplement; $5-$8 for single-use liquid

How to use

For adults: 200-400 mg magnesium citrate daily, taken at night with food or water. Start at the lower dose and adjust as needed. Magnesium citrate liquid (ready-to-drink) at 300 mL as a one-time dose for acute constipation. For chronic constipation, daily supplementation is preferred over single high doses.

How it works

Magnesium citrate is an osmotic laxative - magnesium ions draw water into the intestinal lumen by osmosis, softening stool and stimulating intestinal muscle contractions (peristalsis). Citrate salt form has superior bioavailability and gentler action than magnesium hydroxide.

Where to buy

Natural Vitality Calm Magnesium Supplement (Whole Foods, Target); CVS Health Magnesium Citrate Saline Laxative Liquid (CVS, $5-$8 for acute use); NOW Foods Magnesium Citrate (Amazon, iHerb).

Typical cost: $15-$30 for powder supplement; $5-$8 for single-use liquid

Safety notes

High doses cause diarrhea and cramping - use the lowest effective dose. Avoid in people with kidney disease (impaired magnesium excretion causes toxicity). May interact with antibiotics (tetracyclines, quinolones) - separate by 2 hours. Do not use high-dose magnesium citrate liquid repeatedly without medical supervision. Check with a doctor if on heart medications.

Drug & supplement interactions

  • Always tell your doctor or pharmacist about any supplements you take.
  • Interactions can occur with prescription medications, blood thinners, and immunosuppressants.
  • Herbal remedies can affect how the body absorbs or metabolises drugs.
  • Check drugs.com interactions checker before starting.

Clinical source

Kubota et al., Lactobacillus reuteri DSM 17938 and magnesium oxide in children with functional chronic constipation, Nutrients, 2020

This information is compiled from primary clinical literature and is for informational purposes only. It is not a substitute for professional medical advice. Read our full disclaimer.