Magnesium oxide
MgO
Forms: Tablets and powders sold as a supplement, and a widely used laxative, especially in East Asia. Other magnesium salts have their own cards.
Other esters and forms: Magnesium, Magnesium aspartate, Magnesium carbonate, Magnesium chloride, Magnesium citrate, Magnesium gluconate, Magnesium glycinate (bisglycinate), Magnesium hydroxide, Magnesium L-threonate, Magnesium lactate, Magnesium malate, Magnesium orotate, Magnesium sulfate (Epsom salt), Magnesium taurate
One of the most common forms of magnesium in tablets. It dissolves poorly, so little is absorbed; it is also a laxative, and long-term use can raise blood magnesium with weak kidneys.
Legal status: Sold freely as a supplement and, depending on the country, as an OTC or prescription laxative; not prohibited in sport.
What it gives
What people use it for and what the sources report. Strength is a general category from the literature: mild, clear or strong.
Purpose
Sold as a cheap magnesium supplement for cramps, sleep and recovery, and as a laxative. Because little is absorbed, much stays in the gut, so it replaces sweat losses less efficiently than soluble salts and often loosens stools.
What people seek and what studies show
In absorption studies only about 4% was taken up, less than from chloride, lactate or aspartate. In a small trial in 16 men, oxide lowered resting blood pressure but did not change exercise performance. As a laxative it works, and long-term laxative use with weak kidneys has caused dangerous magnesium build-up.
Effects
Evidence: Approved medicine — studied in people for its medical use
Sought effects by goal (as reported)
Possible side effects
Possible does not mean certain: whether they appear depends on dose, duration, individual response and monitoring. Below — what to watch for and how to notice it early.
2 possible side effects
level · how often it is reportedWhat the levels mean
Level: general category from the literature, not your personal risk
How often
- common
- reported often
- possible
- reported in some people
- rare
- reported occasionally
How to lower the risks
For 2 of 2 possible side effects there are specific ways to lower the chance: everyday measures, supplements and options a doctor may consider. No measure removes a risk completely.
Limit caffeine, pre-workouts and other stimulants; with palpitations, stop the suspected drug, pause hard training and get an ECG. Don’t add potassium on your own (supplements, Asparkam/Panangin, salt substitutes): it is dangerous with spironolactone, ARBs/ACE inhibitors or kidney problems; a blood test shows the level.
How each option helps (1)
- Heart screening: ECG and echocardiogram — An ECG read by athlete criteria separates normal training changes from arrhythmias, conduction or QT problems — key with stimulants, clenbuterol, thyroid hormone or diuretics.
Low-level side effects
How each option helps (2)
- Working with a doctor — Assesses persistent vomiting or severe belly pain (possible pancreatitis or gallstones) and adjusts prescribed GLP-1 treatment when nausea persists.
- Pancreatin + dimeticone (Pankreoflat) — May ease heaviness and gas after meals; can cause nausea or diarrhea. Not for pork or cow's milk protein allergy (anaphylaxis reported) or early acute pancreatitis.
Check-ups and blood tests
Which tests and check-ups to do and when. This is a guide — agree the exact schedule with a sports physician.
Which doctors can help
Get medical help at once if
- Racing or irregular heartbeat that does not settle at rest, dizziness, fainting (especially during exercise), chest pain — call your local emergency number.
In an emergency, call your local emergency number.
For women
For leg cramps in pregnancy, a Cochrane review found the magnesium trials conflicting; in pregnancy, discuss it with a doctor first.
Myth & fact
“Magnesium laxatives are harmless, so long-term use is fine.”
With long-term use, older age or weak kidneys, magnesium can build up to dangerous levels: Japanese doctors described severe cases on oxide laxatives, one fatal. Blood magnesium is often not checked.
Combinations
No specific combination notes for this substance yet. The stack check still adds up side effects that several substances share.
Sources
Possible side effects by body system, combinations, how to lower the risks and which tests to do — free.
Open the stack check