Magnesium citrate: what it treats, how to take it, side effects
Last updated September 3, 2026.
Magnesium citrate is an over-the-counter saline laxative that relieves occasional constipation, usually within half an hour to 6 hours. It draws water into the bowel to trigger a movement, and it is also used to empty the colon before procedures like colonoscopy.
What does it treat?
It treats occasional constipation, the kind that comes and goes, not a chronic pattern. It works fast and thoroughly, which is why clinicians also use it for bowel prep before exams and surgery. If you need a laxative for more than a week, that is a sign to stop self-treating and talk to a doctor.
How do you take it?
Shake the bottle well. Adults and children 12 and over take 6.5 to 10 fluid ounces as a single dose or split up, with no more than 10 fluid ounces in 24 hours; children 6 to under 12 take 3 to 7 fluid ounces. Drink a full 8-ounce glass of liquid with each dose. Chilling the bottle makes it taste better. Take any other medicines at least 2 hours before or after, because magnesium citrate can interfere with their absorption. It is meant for occasional use; do not use it for longer than a week without medical advice.
Side effects to know
- Common: loose or watery stools (that is the drug working), mild abdominal cramping, nausea, and gas.
- Serious: dehydration and electrolyte imbalance from overuse, and in people with kidney disease, dangerous magnesium buildup (slow heartbeat, muscle weakness, confusion, very low blood pressure).
Who should not take it?
Ask a doctor first if you have kidney disease, are on a magnesium-restricted diet, or already take daily laxatives. Abdominal pain with nausea or vomiting, or a sudden change in bowel habits lasting 2 weeks, needs a diagnosis before a laxative. Do not use it when a blockage is possible. Rectal bleeding or no bowel movement after a dose means stop and call a doctor. In pregnancy, use it only on professional advice.
When is it an emergency?
Call 911 for fainting, a very slow heartbeat, severe muscle weakness, or confusion after taking it, which can signal magnesium toxicity, especially with kidney problems. Severe unrelenting abdominal pain with vomiting also warrants emergency care. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
How fast does magnesium citrate work?
The label says it generally produces a bowel movement within 30 minutes to 6 hours. Take it when you can stay near a bathroom, and drink the full glass of water it comes with, since the water is part of how it works.
Can I use magnesium citrate every day?
No. It is for occasional constipation, and the label directs you to ask a doctor if you have already used a laxative for more than a week. Daily reliance on a saline laxative can cause dehydration and electrolyte problems, and it can mask a condition that needs treating.
Is magnesium citrate safe with kidney disease?
It can be dangerous. Kidneys clear magnesium, and when they are impaired, magnesium can build up to toxic levels: slow heartbeat, weakness, confusion, low blood pressure. The label tells people with kidney disease to ask a doctor before any use.
Does magnesium citrate interfere with other medicines?
Yes. It can change how other drugs are absorbed, so take other medications at least 2 hours before or 2 hours after your dose. Antibiotics like tetracyclines and fluoroquinolones are classic examples, but the spacing rule applies broadly.
What does magnesium citrate taste like?
Most people describe it as very tart and lemony with a slight fizz. Chilling the bottle first makes it noticeably easier to drink, and you follow it with a full glass of water anyway.
Is magnesium citrate the same as a magnesium supplement?
No. Magnesium citrate laxative is a large single dose taken to empty the bowel, while daily magnesium supplements are small doses for nutritional purposes. Do not use the laxative as a supplement or vice versa.