Magnesium oxide is formed when magnesium metal reacts with oxygen, producing a white, powdery compound that's packed with elemental magnesium — about 60% by weight, which is higher than most other magnesium forms. It's widely available, affordable, and has been used medicinally for centuries, mainly as an antacid and laxative. While it's not the most absorbable form of magnesium, it still provides meaningful benefits, especially for digestive issues and as a cost-effective way to address deficiency.

Magnesium is involved in over 300 enzyme-driven processes in the body — everything from making energy, to relaxing muscles, to keeping your heart rhythm steady. Magnesium oxide works in the gut partly by drawing water into the intestines (which softens stool and triggers bowel movements) and by neutralizing stomach acid. Once absorbed through the intestinal wall, magnesium supports nerve signaling, muscle relaxation, blood sugar regulation, and healthy stress responses.

Magnesium oxide comes as capsules and tablets for daily supplementation, loose powder for mixing into water or food, and as a liquid suspension (milk of magnesia) for more immediate constipation or heartburn relief. Tablets and capsules are the most convenient for daily use; the liquid suspension acts faster for digestive complaints.

• Constipation
• Heartburn and acid reflux
• Magnesium deficiency
• Muscle cramps and spasms
• Migraines and headaches
• Sleep problems and insomnia
• High blood pressure
• Anxiety and stress
• Blood sugar regulation (type 2 diabetes support)

• Magnesium deficiency-related complications (including cardiovascular risk and bone loss with long-term adequate intake)
• Migraine frequency reduction with consistent supplementation

• Pumpkin seeds (pepitas) — Among the highest natural sources of magnesium — a small handful gives you nearly half your daily target.
• Dark leafy greens (spinach, Swiss chard) — Chlorophyll contains magnesium at its core, making cooked spinach and chard excellent everyday sources.
• Black beans and legumes — A cup of cooked black beans delivers around 120 mg of magnesium along with fiber and protein.
• Dark chocolate (70%+ cacao) — A 30g square of good dark chocolate provides around 50 mg of magnesium — a genuinely enjoyable way to top up.
• Whole grains (brown rice, quinoa, oats) — Magnesium is concentrated in the bran layer, so whole grains provide meaningfully more than refined versions.

• Loose stools or diarrhea (most common, especially above 350 mg/day)
• Nausea or stomach discomfort
• Abdominal cramping or bloating
• Diarrhea leading to dehydration if overused as a laxative
• Very high doses: low blood pressure, muscle weakness, irregular heartbeat (rare, mainly in people with kidney problems)

• Recommended daily: 200–400 mg of elemental magnesium per day for general supplementation; up to 400–800 mg for constipation relief (short-term). The UK/US RDA for adults is 310–420 mg total daily magnesium from all sources.
• Best time of day: For general supplementation or sleep support, take in the evening. For constipation or heartburn, take as needed. Splitting the dose into morning and evening can reduce digestive side effects.
• With or without food: Take with food or a large glass of water to reduce the chance of stomach upset. For antacid or laxative use, taking on an empty stomach speeds the effect.
• Time to effect: Constipation relief: 30 minutes to 6 hours. Muscle cramps, sleep, and mood: 2–4 weeks of consistent daily use. Migraine prevention: 8–12 weeks.
• How long to take it: Magnesium is an essential mineral — daily supplementation can be ongoing if dietary intake is inadequate. For constipation, use only as needed and avoid daily laxative reliance long-term. Reassess need every 3–6 months.