Magnesium hydroxide
Milk of magnesia, Phillips' Milk of Magnesia
Forms: Milk of magnesia suspension (antacid and laxative) and antacid mixes with aluminium hydroxide. 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 L-threonate, Magnesium lactate, Magnesium malate, Magnesium orotate, Magnesium oxide, Magnesium sulfate (Epsom salt), Magnesium taurate
Milk of magnesia: an over-the-counter antacid for heartburn and a saline laxative for occasional constipation. It is not meant as a magnesium supplement.
Legal status: Sold over the counter as an antacid and laxative in most countries; 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
Used for heartburn, acid indigestion and occasional constipation; it is not meant as a magnesium supplement, though some athletes use laxatives to make weight. Labels limit use without a doctor's advice and say to ask a doctor first with kidney disease.
What people seek and what studies show
As an antacid it eases heartburn; as a laxative it usually works within hours. Severe high blood magnesium has been reported with regular use, mostly with kidney failure or a blocked bowel, sometimes fatally. A combat-sport review lists laxatives among rapid weight-loss methods that harm performance and health.
Effects
No clear training effect in the sources.
Evidence: Approved medicine — studied in people for its medical use
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.
3 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 3 of 3 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.
Drink to thirst, more in heat and long sessions, with sodium-containing drinks; far beyond thirst risks low sodium. No weight cutting by dehydration. With diuretics, ARBs/ACE inhibitors or kidney problems: potassium products or salt substitutes only after a blood test and a doctor’s advice.
How each option helps (14)
- Fluid & electrolyte management — Weighing before and after training shows sweat loss; ACSM advises keeping it under about 2% of body weight. Salty fluids help but don't prevent the losses diuretics cause.
- Electrolytes (sodium, potassium, magnesium) — Replacing sweat sodium and fluid may lower the chance of dehydration and heat cramps; it does not remove heat-illness risk or make diuretics or water cuts safe, and its potassium is risky with ARBs.
- Magnesium — Replaces magnesium lost in sweat or with diuretics; evidence that it prevents exercise cramps is lacking. It does not make diuretic use or extreme weight cutting safe.
- Magnesium aspartate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium carbonate — Supplies magnesium, but it is used mainly as an antacid and there are few data on it as a supplement; chalk on the hands supplies none. Does not make diuretics safe.
- Magnesium chloride — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium citrate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium gluconate — Replaces magnesium lost in heavy sweat or with diuretics. Cochrane found no trials in exercise cramps; runners who cramped did not have lower blood magnesium. Does not make diuretics safe.
- Magnesium glycinate (bisglycinate) — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium lactate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium malate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium orotate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium oxide — Supplies some magnesium, but far less is absorbed than from soluble salts; Cochrane found no trials in exercise cramps. Does not make diuretics safe.
- Magnesium taurate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
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.
- Severe cramps, marked weakness, palpitations, dizziness on standing, very little urine — seek urgent care. Vomiting, confusion or a seizure after a long event can mean low sodium — do not drink more, call your local emergency number.
In an emergency, call your local emergency number.
Myth & fact
“Milk of magnesia before weigh-in just empties the gut and does no harm.”
A combat-sport review lists laxatives among rapid weight-loss methods harmful to performance and health. Regular use has caused fatal magnesium build-up, even with normal kidneys when the bowel was blocked.
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