How long does magnesium citrate take to work?

Magnesium citrate is an over-the-counter liquid laxative combining magnesium and citric acid, used for occasional constipation. It can produce a bowel movement within 30 minutes to 6 hours after ingestion. If no response occurs by 6 hours, contact your healthcare provider for advice.

Benefits of magnesium citrate

In liquid form (brands like Citroma or Citrate of Magnesia), it relieves constipation. In pill form, it supplements dietary magnesium for:

  • Bone health
  • Muscle function
  • Blood sugar regulation
  • Migraine prevention
  • Heart health and blood pressure control

Mechanism of action for constipation

Acts as an osmotic (saline) laxative by:

  • Relaxing bowel muscles
  • Drawing water into the intestines
  • Softening stool and increasing bowel movement frequency

Common side effects

  • Stomach pain or cramps
  • Bloating and gas
  • Nausea
  • Diarrhea

Serious side effects (rare)

  • Allergic reaction (hives, facial or throat swelling, breathing difficulty)
  • Irregular heartbeat
  • Low blood pressure
  • Muscle weakness
  • Drowsiness or confusion
  • Dizziness
  • Dehydration and electrolyte imbalance
  • Bloody stools or rectal bleeding

Safety precautions

Usually safe when used as directed. Inform your provider if you have:

  • Kidney disease
  • Neuromuscular disorders (e.g., myasthenia gravis)
  • Intestinal blockage
  • Heart disease
  • Magnesium- or sodium-restricted diet
  • Pregnancy or breastfeeding

Drug interactions

May affect or be affected by:

  • Antibiotics (quinolones, tetracyclines, aminoglycosides, nitrofurantoin)
  • Blood pressure medications (calcium channel blockers, diuretics)
  • Certain HIV, diabetes, seizure, and cancer drugs
  • Digoxin

Recommended adult dose for constipation

One 10 fl oz (300 ml) bottle by mouth in 24 hours, either as a single dose or divided doses. Beginners may start with 6.5 fl oz (195 ml). Do not exceed one bottle in 24 hours.

Administration instructions

  • Shake well before use.
  • Take on an empty stomach (1 hour before or 2 hours after a meal).
  • Drink a full glass of water (8 oz/240 ml) afterward.
  • Ensure bathroom access for the next 6 hours.

Sources

  • DailyMed: Citroma magnesium citrate liquid (2018)
  • NHS: Constipation
  • MedlinePlus: Magnesium citrate
  • NIH Office of Dietary Supplements: Magnesium
  • Werner T, et al. Magnes Res. 2019