Antacids — Medication Guide, Uses & Safety — Uses, Dosage & Side Effects | MyMedicPlus

Antacids are over-the-counter (OTC) medications that work by directly neutralizing excess stomach acid to provide rapid symptomatic relief from heartburn, acid indigestion, sour stomach, and acid reflux. They are some of the most widely used self-care remedies globally. Common active ingredients include calcium carbonate (e.g. Tums), magnesium hydroxide (e.g. Milk of Magnesia), aluminium hydroxide (e.g. Maalox), and sodium bicarbonate (e.g. Alka-Seltzer). Combination products containing both magnesium and aluminium are used to balance the opposing constipating and laxative effects of each ingredient. Antacids act rapidly — typically within minutes — but their duration of action is short at 1–3 hours; they do not reduce acid production like proton pump inhibitors (PPIs) or H2 receptor antagonists. They are not suitable as sole long-term therapy for gastroesophageal reflux disease (GERD). FDA-approved and widely available in pharmacies and supermarkets without a prescription.

Antacids provide effective symptomatic relief of heartburn, acid indigestion, sour stomach, and mild gastric discomfort caused by excess stomach acid. They are commonly used as first-line OTC treatment before escalating to prescription acid-suppressing medications. Primary on-label uses include occasional heartburn and acid reflux, indigestion after meals, and stomach upset. In patients with chronic kidney disease, aluminium-containing antacids are prescribed under medical supervision as phosphate binders to reduce elevated blood phosphate levels (hyperphosphatemia). Calcium carbonate antacids also serve as supplemental calcium sources for bone health in those with dietary deficiency. Antacids are typically prescribed or recommended by general practitioners (GPs), gastroenterologists, and pharmacists. They do not treat the underlying cause of acid overproduction and should not be used long-term without a definitive diagnosis.

Antacids work by directly neutralizing hydrochloric acid (HCl) in the stomach through a chemical acid-base reaction, rapidly raising gastric pH from its normally acidic level (pH 1–3) toward a more neutral value (pH 4–7). Calcium carbonate reacts with stomach acid to produce calcium chloride, water, and carbon dioxide (which causes belching). Magnesium hydroxide reacts to form magnesium chloride and water. Aluminium hydroxide reacts to form aluminium chloride and water. This rapid pH elevation reduces the corrosive effect of acid on the esophageal mucosa and stomach lining, relieving the burning sensation characteristic of heartburn. The rise in pH also reduces the activation of pepsin, the digestive enzyme that can further irritate inflamed stomach and esophageal tissue. Effects are generally felt within 5–15 minutes, making antacids one of the fastest-acting stomach acid remedies available without prescription.

Typical adult dose is 1–4 chewable tablets or 10–20 mL of liquid suspension, taken 1–3 hours after meals and at bedtime when acid reflux symptoms typically peak. For immediate onset of symptoms, antacids may be taken at any time. Always chew tablets thoroughly before swallowing to ensure effective dissolution and mixing with stomach acid; do not swallow them whole. Maximum daily dose varies significantly by product and active ingredient — always follow the label instructions carefully, as exceeding limits increases the risk of adverse effects. Effervescent tablets should be fully dissolved in water before drinking. For children, use age-appropriate pediatric formulations and dosing as directed on the label or by a pharmacist. Do not use antacids as a long-term substitute for diagnosing and treating underlying gastric pathology. Consult your doctor if symptoms occur more than twice per week or if antacids are needed daily.

Side effects vary by the active ingredient. Calcium carbonate antacids (e.g. Tums) commonly cause constipation (in approximately 5–10% of users), belching, and gas from carbon dioxide production. With excessive or prolonged use, calcium carbonate can cause hypercalcemia (elevated blood calcium), presenting as nausea, weakness, kidney stones, and confusion — known as milk-alkali syndrome. Magnesium-based antacids (e.g. magnesium hydroxide) commonly cause loose stools and diarrhea, which can be significant at higher doses. Aluminium hydroxide frequently causes constipation and, with long-term use, can deplete blood phosphate levels (hypophosphatemia), weakening bones and muscles. Sodium bicarbonate products release carbon dioxide (causing belching and gas) and deliver a significant sodium load — they must be avoided by patients on low-sodium diets, those with heart failure, hypertension, or edema. Combination antacids (aluminium-magnesium) balance laxative and constipating effects for most users. Rare systemic alkalosis can occur with excessive antacid use.

Antacids can significantly impair the absorption of numerous co-administered medications by binding them in the gastrointestinal tract or altering gastric pH. Drugs that must be taken separately from antacids include antibiotics (tetracyclines such as doxycycline and fluoroquinolones such as ciprofloxacin — antacids reduce their absorption by up to 90%), thyroid replacement therapy (levothyroxine — separate by at least 4 hours), iron supplements, bisphosphonates for osteoporosis (alendronate — take 30 minutes before antacids), HIV antivirals, and some antifungals. Always take these medicines at least 1–2 hours before or 2–4 hours after antacids. Patients with kidney disease should avoid magnesium-containing antacids without medical supervision due to risk of magnesium accumulation (hypermagnesemia). Frequent long-term antacid use without medical evaluation may mask symptoms of peptic ulcer disease or gastric cancer. Seek medical evaluation promptly if heartburn occurs more than twice a week, if symptoms persist despite antacid use, if there is pain or difficulty swallowing, unexplained weight loss, or blood in vomit or stools.