Antacids & Stomach Medications — Drug Absorption Interactions Explained
Antacids are among the most commonly used OTC medications, but they can interfere with the absorption of antibiotics, thyroid medication, iron, and more. Timing matters.
Types of Antacids and How They Work
Antacids neutralise stomach acid and include calcium carbonate (Tums), aluminium hydroxide, magnesium hydroxide, and sodium bicarbonate. They provide fast but temporary relief of heartburn and acid indigestion. Proton pump inhibitors (PPIs) such as omeprazole and esomeprazole, and H2 blockers such as famotidine, suppress acid production rather than neutralising it — they work differently and have different interaction profiles.
Drugs Whose Absorption Antacids Reduce
①Antibiotics (quinolones like ciprofloxacin; tetracyclines like doxycycline): Calcium, magnesium, and aluminium in antacids bind to these antibiotics and reduce absorption by 50% or more. Space them by at least 2 hours. ②Thyroid medication (levothyroxine): Must be taken on an empty stomach, 30–60 minutes before any other medication or food; antacids significantly reduce its absorption. ③Iron supplements: Calcium and magnesium impair iron absorption. Allow at least 2 hours between them. ④Bisphosphonates (alendronate for osteoporosis): Must be taken with 200 ml of plain water on an empty stomach; never combined with antacids.
Risks of Long-Term PPI Use
Short-term PPI use is generally safe, but taking omeprazole or similar drugs for more than a year without medical oversight increases the risk of: ①magnesium deficiency (muscle cramps, arrhythmia), ②reduced calcium absorption (osteoporosis risk), ③vitamin B12 deficiency, ④increased susceptibility to Clostridioides difficile infection. Do not self-medicate with PPIs for months on end — they are meant to treat a specific condition, not suppress daily symptoms indefinitely.
When Antacids Are Not Enough
Frequent heartburn may signal gastro-oesophageal reflux disease (GERD), a peptic ulcer, or H. pylori infection. Treating symptoms with antacids while an underlying condition goes undiagnosed delays proper treatment and can allow complications to develop. If you rely on antacids more than twice a week or have heartburn lasting more than two weeks, see a doctor to find the root cause.