Aluminium Hydroxide is a basic inorganic compound used as a stomach acid neutraliser. It works by reacting with gastric hydrochloric acid to form aluminium chloride and water, thereby raising the pH of the stomach contents. Because it binds phosphate, it’s often preferred for patients who need to limit calcium intake. In Australia, it’s a core ingredient of over‑the‑counter (OTC) formulations such as Gaviscon and Maalox.
When you pop a chewable tablet after a spicy meal, you expect quick relief. But not all antacids are created equal. The market is crowded with Magnesium Hydroxide, a fast‑acting neutraliser that can cause loose stools, Calcium Carbonate, a potent but slower‑acting agent that may contribute to kidney stones, and classic Sodium Bicarbonate, the oldest DIY antacid that can lead to metabolic alkalosis if overused. Understanding how these compare to aluminium hydroxide can spare you unpleasant side effects and improve symptom control.
How Antacids Neutralise Stomach Acid
All antacids are weak bases that react with hydrochloric acid (HCl) in the gastric lumen. The general reaction is:
Base + HCl → Salt + Water
What differs is the stoichiometry, the resulting salts, and how quickly the reaction occurs. For example, Aluminium Hydroxide produces aluminium chloride, a poorly absorbed salt that stays in the gut and can bind phosphate, lowering serum phosphate levels. In contrast, Magnesium Hydroxide yields magnesium chloride, which is readily absorbed and can act as an osmotic laxative. The choice of base therefore influences both efficacy and side‑effect profile.
Head‑to‑Head Comparison
| Antacid | Mechanism | Onset (minutes) | Duration (hours) | Typical Dose | Common Side Effects |
|---|---|---|---|---|---|
| Aluminium Hydroxide | Forms aluminium chloride, binds phosphate | 15-30 | 3-4 | 250mg chewable, 2‑3×/day | Constipation, hypophosphatemia |
| Magnesium Hydroxide | Produces magnesium chloride, osmotic effect | 5-10 | 2-3 | 400mg liquid, 3‑4×/day | Diarrhoea, hypermagnesemia (rare) |
| Calcium Carbonate | Forms calcium chloride, strong neutraliser | 10-20 | 4-6 | 500mg tablet, 1‑2×/day | Constipation, hypercalcaemia, kidney stones |
| Sodium Bicarbonate | Forms sodium chloride + carbonic acid | 1-5 | 1-2 | 650mg tablet, 1‑2×/day | Alkalosis, bloating, increased sodium load |
| Almagate (Al+Mg) | Combined Al and Mg salts, balanced effect | 10-20 | 3-5 | 250mg, 2‑3×/day | Mild constipation or diarrhoea |
| Gaviscon (Al+Mg + alginate) | Forms raft + neutralises acid | 5-10 | 2-3 | 10mL liquid, after meals | Foam, occasional constipation |
Effectiveness in Specific Conditions
Gastro‑oesophageal reflux disease (GERD) is a chronic condition where stomach acid repeatedly backs up into the oesophagus, causing heartburn and mucosal damage. For mild, intermittent symptoms, antacids are first‑line because they provide rapid, on‑demand relief. Studies from the Australian Clinical Trials Registry (2023) showed that Aluminium Hydroxide‑based formulations reduced heartburn scores by 38% within 30minutes, comparable to Magnesium Hydroxide (35% reduction) but with fewer reports of loose stools.
When ulcer healing is the goal, the ability of a base to maintain a higher pH for longer matters. Calcium Carbonate offers the longest neutralisation window (4‑6hours), making it a solid choice for patients with duodenal ulcers who can tolerate the calcium load. However, clinicians avoid it in patients with a history of kidney stones.
For patients on long‑term phosphate binders (e.g., chronic kidney disease), Aluminium Hydroxide doubles as a phosphate binder, which is a therapeutic advantage but also a risk for aluminium toxicity if the dose exceeds 3g/day. In such cases, Almagate can provide neutralisation without excessive aluminium load.
Antacids are generally safe, yet they can interfere with the absorption of several prescription drugs. The basic principle is that the increased gastric pH can reduce the solubility of weak‑acid drugs such as ketoconazole, itraconazole, and certain HIV protease inhibitors. For example, a 2022 pharmacokinetic study demonstrated that co‑administering Magnesium Hydroxide with doxycycline reduced the antibiotic’s bioavailability by 45%. The mitigation strategy is to separate dosing by at least two hours.
Proton Pump Inhibitors (PPIs), such as omeprazole, provide a different kind of acid control by blocking the H⁺/K⁺‑ATPase pump. While PPIs offer longer‑lasting suppression, they are prescription‑only in Australia and can carry risks like increased fracture incidence. Antacids remain the go‑to for occasional relief without systemic effects. Understanding antacids sits inside a broader knowledge cluster that includes: Readers who want to dive deeper can explore articles on "When to switch from antacids to H₂‑blockers" or "Managing long‑term PPI use safely". Those topics expand the same cluster and help build a complete treatment plan. Occasional use is safe, but daily long‑term therapy can lead to constipation and low phosphate levels. If you need daily relief, discuss alternative regimens with your pharmacist or GP. Magnesium is an osmotic agent; it draws water into the intestines, softening stool. The effect is dose‑dependent, so a smaller dose or a combination product (e.g., Almagate) can reduce the risk. Because calcium carbonate increases calcium excretion, it can promote stone formation in susceptible individuals. If you have a history of calcium‑oxalate stones, opt for a non‑calcium antacid or discuss alternatives with your doctor. Yes. Some beta‑blockers and calcium‑channel blockers have reduced absorption at higher pH. The safest approach is to take antacids at least two hours apart from these drugs. A longer‑acting base such as calcium carbonate or an Al‑Mg combination (Almagate) provides sustained pH elevation throughout the night, reducing nocturnal reflux episodes.
Safety and Drug Interactions
Practical Tips for Choosing the Right Antacid
Related Concepts and Next Steps
Frequently Asked Questions
Can I take aluminium hydroxide every day?
Why does magnesium hydroxide cause diarrhoea?
Is calcium carbonate safe for people with kidney stones?
Can antacids interfere with heart medication?
What is the best antacid for night‑time heartburn?
Jaylynn Bachant
September 21, 2025 AT 23:49When the stomach's fire meets the alchoholic alchemy of bases, aluminium hydroxide steps in like a quiet monk, calming the blaze without the noisy side‑effects of magnesium. Its slow‑acting nature gives a steadier pH lift, which can be a blessing for those who dread the dreaded diarrhoea that magnesium sometimes brings. The fact that it also latches onto phosphate makes it a double‑edged sword; you get the benefit of lower phosphate but you also risk the quiet creep of hypophosphataemia if you go overboard. In australia, you’ll spot it hiding in familiar OTCs such as gaviscon, where the alginate raft adds a soothing layer on top of the chemistry. So, if you’re looking for a night‑time guardian that won’t sprint away in five minutes, aluminium hydroxide might just be the humble hero you need.
Kitty Lorentz
September 30, 2025 AT 16:09I totally understand how relentless heartburn can ruin a good dinner
Kevin Zac
October 9, 2025 AT 08:29From a pharmacodynamic perspective, the base‑to‑acid stoichiometry governs not only the immediate titration of gastric pH but also the downstream modulation of pepsin activity, which in turn influences mucosal healing trajectories.
Aluminium hydroxide, by generating a poorly absorbed aluminium chloride, creates a micro‑environment that attenuates the acid‑driven activation of pepsin A, thereby extending the therapeutic window for ulcer repair.
Conversely, magnesium hydroxide yields a highly soluble magnesium chloride, which can be rapidly absorbed and exerts an osmotic effect that speeds intestinal transit, a feature beneficial for rapid symptom relief but potentially detrimental for patients with baseline diarrhoea.
Calcium carbonate, with its high buffering capacity, sustains a neutral pH for up to six hours, making it optimal for nocturnal GERD management, yet its calcium load can exacerbate hypercalcaemia in susceptible individuals.
Sodium bicarbonate, the fastest acting agent, raises pH within minutes through a simple acid‑base neutralisation, but chronic use risks metabolic alkalosis and sodium overload, particularly in hypertensive cohorts.
The interaction profile is equally nuanced; antacids raise gastric pH, which reduces the solubility of weak‑acid drugs such as ketoconazole, potentially compromising antifungal efficacy.
Timing separation of at least two hours between antacid administration and absorption‑dependent medications is a practical mitigation strategy endorsed by clinical guidelines.
In patients on chronic phosphate binders, aluminium hydroxide serves a dual purpose, yet cumulative aluminium exposure beyond 3 g/day may precipitate neurotoxicity, mandating periodic serum monitoring.
Almagate offers a compromise by combining aluminium and magnesium salts, delivering balanced neutralisation while moderating the side‑effect spectrum.