How to Use Magnesium Hydroxide for Acid Reflux Relief (Doses, Timing, Safety, NZ 2025)

You want fast relief from that throat burn without making things worse later. This guide shows you exactly how to use magnesium hydroxide (often sold as milk of magnesia or in combo antacids) to calm occasional acid reflux-safely, without guesswork, and with New Zealand realities in mind. Expect quick relief tips, precise dosing, timing with meals and medicines, signs to stop, and what to try next if it’s not cutting it.

TL;DR / Key takeaways

• What it does: Neutralises stomach acid fast. Relief usually starts in 15-30 minutes and lasts about 1-3 hours. Great for occasional heartburn, not a cure for chronic reflux.
• Dose basics (adults): Follow the label. Typical antacid dose is 5-15 mL of liquid (often 400 mg/5 mL) or 2-4 chewable tablets when symptoms hit. Don’t exceed the daily max on the pack.
• Timing: Take at symptom onset or after trigger meals. Separate from other medicines-2 hours for most, 4 hours for levothyroxine, tetracyclines, and fluoroquinolones.
• Side effects: Diarrhoea is the main one. Avoid if you have significant kidney disease unless your doctor says otherwise.
• When to escalate: Heartburn ≥2 times a week for 3+ weeks, night-time symptoms, or red flags (trouble swallowing, bleeding, weight loss, chest pain) → see your GP. You may need an H2 blocker or PPI.

How to use magnesium hydroxide for fast, safe relief

Quick reality check: antacids are for here-and-now relief. They don’t heal inflammation in the oesophagus or stop reflux at its source. If your symptoms are occasional (big meals, spicy food, coffee, wine), magnesium hydroxide is a good choice because it works quickly and is easy to find in NZ pharmacies and supermarkets.

Here’s a simple, step-by-step way to use it well:

1. Make sure it’s heartburn. Think burning behind the breastbone, sour taste, worse after meals, bending, or lying down. If the discomfort feels like pressure spreading to your jaw/arm, you’re breathless, sweaty, or the pain is crushing-call emergency services. Don’t wait.
2. Pick your product. You’ll see liquids labelled “milk of magnesia” or combination antacids that include magnesium hydroxide. Chewables are handy on the go; liquids act a touch faster and are easier to measure.
3. Read the strength. Many liquids in NZ list 400 mg per 5 mL. Chewables list mg per tablet. The label tells you the antacid dose, which is usually several times smaller than the laxative dose.
4. Take the dose at the right time. Use it when symptoms start or after eating trigger foods. You can also take it before bed if night-time reflux is a thing for you. Shake liquids well. Chew tablets thoroughly, then drink a glass of water.
5. Separate it from other medicines. As a rule: 2 hours before/after most meds. Make it 4 hours for levothyroxine, tetracyclines, and fluoroquinolones. Ask your pharmacist if in doubt.
6. Expect quick relief. It should help within 15-30 minutes. If it doesn’t touch the sides, you can take another dose as per the label, but don’t exceed the daily maximum.
7. Watch your gut. Magnesium can loosen stools. If you get diarrhoea, reduce the dose or switch to an alginate or a calcium carbonate antacid instead.
8. Set a usage limit. Using antacids most days or most nights for more than two to three weeks? Time to speak with your GP or pharmacist about longer-acting treatment.

From my kitchen in Dunedin after a too-spicy laksa, my move is: chew two tablets right after I put my bowl down, then sit upright for at least an hour. On nights when reflux wakes me, I keep a small liquid bottle on the bedside table-but if I need that more than a couple of times a week, I reassess.

Doses, timing, interactions, and NZ-specific tips

Adult dosing (antacid use)

• Liquid (commonly 400 mg/5 mL): 5-15 mL per dose as needed. Some labels allow dosing up to 4 times a day. Always follow your specific product’s directions.
• Chewables: often 311-500 mg per tablet. Typical dose is 2-4 tablets as needed. Chew well, then drink water.
• Laxative dosing is much higher (e.g., 30-60 mL), which is not what you want for reflux. If you cross into laxative doses, expect diarrhoea.

Timing tips that actually help

• After a trigger meal: take a dose when symptoms start or about 30 minutes after the meal.
• Bedtime reflux: take a dose right before lying down, then elevate the head of your bed by 10-15 cm or use a wedge pillow.
• Active day: stick with chewables you can take when you’re out; liquids rule at home.

Medicine interactions (why spacing matters): magnesium binds certain drugs and blocks absorption. Separate by the times below, or ask your pharmacist if your list is long.

• 4 hours: levothyroxine; tetracyclines (e.g., doxycycline); fluoroquinolones (e.g., ciprofloxacin); bisphosphonates (e.g., alendronate).
• 2 hours: iron supplements; zinc; calcium; some antifungals; some heart meds. If you’re unsure, 2 hours is a safe default.
• PPIs/H2 blockers: fine to combine. Use the antacid for breakthrough symptoms; it will not cancel your omeprazole or famotidine.

Who should check with a clinician first

• Chronic kidney disease, especially moderate-severe (risk of high magnesium levels).
• Myasthenia gravis (magnesium can worsen muscle weakness).
• Pregnancy with frequent reflux-safe for occasional use, but if you’re needing it often, consider alginates or a PPI after discussing with your midwife/GP.
• Children under 12-ask your pharmacist about dosing and better options.

NZ context and what you’ll see on shelves

In New Zealand, antacids are available without a prescription at pharmacies and supermarkets. Labels vary, so check the magnesium hydroxide content per 5 mL (liquid) or per tablet. Combination antacids often pair magnesium hydroxide with aluminium hydroxide or simethicone; that combo can balance stool effects and reduce gas. If you prefer low-sugar or low-sodium options, scan the label-there are sugar-free versions and some alginate products have notable sodium.

Evidence check

Guidance from the American College of Gastroenterology (2022), NICE dyspepsia/GERD guidance (updated 2024), and New Zealand primary care resources agree: antacids and alginates are first-line for symptom relief; H2 blockers and PPIs are used when symptoms are frequent, severe, or complicated. Medsafe datasheets classify magnesium hydroxide as an over-the-counter antacid/laxative with known interactions and renal cautions.

Side effects, red flags, and who should avoid it

Common side effects

• Diarrhoea, stomach cramping, nausea. Usually mild and dose-related. Cut back the dose or switch to an alginate or a calcium carbonate antacid.
• Chalky aftertaste. Chase with a glass of water or sugar-free gum.

Serious but uncommon: high magnesium levels (hypermagnesaemia)

Risk rises in significant kidney impairment or when taking very high doses for many days. Watch for flushing, dizziness, muscle weakness, drowsiness, slow heart rate, or low blood pressure. If these happen, stop and seek urgent care.

Red flags-don’t self-treat, get checked

• Heartburn that wakes you most nights or needs daily antacids for weeks.
• Food or pills feel stuck; painful swallowing.
• Unexplained weight loss, persistent vomiting, black or blood-streaked stools.
• Chest pain with shortness of breath, sweating, or radiation to jaw/arm.
• New-onset reflux after age 55 or a strong family history of upper GI cancer.

Special groups

• Pregnancy and breastfeeding: occasional antacid use is considered safe. Alginates are a good first choice in pregnancy. If you need daily relief, discuss an H2 blocker or PPI with your midwife/GP.
• Kidney disease: avoid unless your clinician okays it. Safer alternatives may be alginates or adjusted therapy.
• Older adults: check kidney function and medicine lists for interactions.
• Children: for persistent reflux, see a GP. Don’t give antacids to infants without advice.

Label pitfalls to avoid

• Confusing laxative dosing with antacid dosing-big difference. Always read the “for heartburn” directions.
• Not shaking liquid well-dose can be off if the magnesium settles.
• Stacking different antacids and blowing past maximum daily doses. Choose one and stick with it.

Alternatives, combos, and when to switch plans

If magnesium hydroxide helps but causes diarrhoea, swap to a calcium carbonate antacid or an alginate. If it doesn’t help enough, layer your strategy:

• For after-meal flare-ups: alginate after meals + antacid for breakthrough.
• For frequent daytime symptoms (most days): consider a short course of an H2 blocker (famotidine) with antacid as needed.
• For daily, severe, or night-time reflux: talk to your GP about a PPI (e.g., omeprazole) for 2-8 weeks, plus lifestyle changes. Keep antacid for breakthrough.
• For pregnancy: start with lifestyle changes and alginates; use magnesium hydroxide or calcium carbonate if needed, and escalate only with clinician advice.

Quick decision guide

• Occasional heartburn (≤1-2 times/week): keep a fast antacid (magnesium hydroxide or calcium carbonate). Add alginate for after-meal protection.
• Frequent symptoms (≥2 times/week): see your GP/pharmacist. Try H2 blocker or PPI. Use antacid for breakthrough.
• No relief from antacids at all: wrong diagnosis? Time for a medical review.

Lifestyle tweaks that actually move the needle

• Evening: avoid large meals 3 hours before bed; raise the head of the bed 10-15 cm; sleep on your left side.
• Meals: smaller portions; go easy on alcohol, chilli, fatty foods, chocolate, coffee, and mint if they trigger you.
• Weight: even a 5-10% loss can reduce reflux pressure if you carry weight around the middle.
• Nicotine: quitting helps the valve at the base of your oesophagus close better.
• Clothes: skip tight belts or shapewear that compress your stomach after meals.

Packaging checklist (grab the right bottle/tablets):

• Strength per 5 mL or per tablet is clear.
• Sugar-free if you have diabetes or prefer to avoid sugar.
• Low sodium if you’re on a sodium-restricted plan (consider alginate sodium content).
• Child-resistant cap if there are kids in the house.

Mini‑FAQ and troubleshooting

Is milk of magnesia the same as magnesium hydroxide? Yes. “Milk of magnesia” is the common name for a liquid suspension of magnesium hydroxide. It’s sold as both an antacid and a laxative-dose and intent differ.

How fast will it work? Relief usually starts in 15-30 minutes. Liquids act slightly faster than chewables.

Can I take it with my PPI or H2 blocker? Yes. Use it for breakthrough symptoms. If you take your PPI in the morning, you can take the antacid later in the day as needed.

Is it safe in pregnancy? Occasional use is considered safe. Many clinicians prefer alginates first. If you need regular relief, ask about famotidine or a PPI like omeprazole.

Will I get dependent on it? No. But if you rely on it often, you might be masking a problem that needs longer-acting treatment. Don’t self-treat daily reflux for weeks without a plan.

What if I get diarrhoea? Lower the dose or switch to an alginate or calcium carbonate product. Stay hydrated.

Can it cause kidney stones? Not typically. The kidney issue here is accumulation of magnesium in people with reduced kidney function, not stones.

How long can I use it? For occasional symptoms as needed. If you need it most days for more than two to three weeks, talk to your GP or pharmacist.

Any food interactions? Food can buffer acid and may slightly delay onset, but you can take it with or after meals. Avoid taking it at the same moment as mineral supplements that compete for absorption.

Does it heal oesophagitis? No. It neutralises acid but doesn’t heal inflammation. That’s a job for PPIs, usually for several weeks.

What do guidelines say? ACG (2022) and NICE (updated 2024) recommend antacids/alginates for quick relief and PPIs for frequent or complicated GERD. NZ primary care guidance echoes this. Medsafe product data outlines dosing and safety points above.

When should I see a GP in NZ? If symptoms are frequent, severe, new after age 55, or you have red flags. Also if you’re on long-term meds that interact or you have kidney disease.

What about alcohol or coffee? Both can trigger reflux by relaxing the lower oesophageal sphincter. If you notice a pattern, cut back or shift to earlier in the day-and keep an antacid handy.

Can I give it to my teen? Teens can usually use adult antacid dosing, but check the label and ask your pharmacist to be sure.

Next steps

• If magnesium hydroxide settles your occasional heartburn: keep using it on demand, track your triggers, and keep doses within the label.
• If you need it most days: book a chat with your GP or pharmacist. You may benefit from a time-limited PPI, a check for medicines that worsen reflux (e.g., NSAIDs), or testing for H. pylori if dyspepsia is prominent.
• If you hit a red flag: stop self-treating and seek medical assessment.

Troubleshooting by scenario

• No relief after two proper doses: try an alginate or a calcium carbonate antacid next time; if symptoms persist, consider an H2 blocker or see your GP.
• Relief, but diarrhoea: reduce the dose or switch to alginate/calcium carbonate; avoid laxative-strength milk of magnesia.
• Night-time-only reflux: try an alginate after dinner and before bed, elevate the head of the bed, avoid late meals. Keep antacid for wake-ups.
• On multiple meds: keep a note in your phone with dose times; set a 2-4 hour buffer around sensitive medicines.
• Pregnancy nausea + reflux: ginger or B6 for nausea; use alginate/antacid for reflux; small frequent meals; ask your midwife about safe escalations if needed.

Done right, magnesium hydroxide is a simple, fast tool. Keep it in your cupboard, use it with intention, and let your symptoms tell you when it’s time to switch gears.