Antacids (Maalox, Gaviscon, Rennie)
Provide immediate relief from heartburn — work in minutes but only last 1-2 hours. Best for occasional symptoms or breakthrough on top of regular PPI/H2 treatment.
This article is educational and does not replace your doctor's advice. Seek urgent care for any red-flag symptoms.
Drug class
Antacids (acid neutralizers) and alginates
Examples
Maalox, Mylanta (aluminum + magnesium hydroxide), Tums (calcium carbonate), Gaviscon and Gaviscon Advance (alginate that forms a raft on top of stomach contents — very useful for nighttime reflux), Rennie (calcium + magnesium carbonate).
How it works
Antacids neutralize stomach acid that is already there — providing fast relief but no protection against new acid being produced. Alginates (in Gaviscon) form a foam "raft" that floats on top of stomach contents and physically blocks reflux for 30-60 minutes.
What it treats
- Occasional heartburn (less than twice a week)
- Breakthrough symptoms while on PPI or H2 blocker
- Nighttime reflux (especially Gaviscon Advance)
- Pregnancy heartburn (preferred over PPIs in mild cases)
How to take it
Take when symptoms occur. Liquid forms work faster than tablets. Chew tablets thoroughly. For maximum effect: take 1 hour after meals and at bedtime. Don't take within 2 hours of other medications (interferes with absorption).
Common side effects
- Aluminum-containing antacids: constipation
- Magnesium-containing antacids: diarrhea
- Calcium-containing antacids: constipation, kidney stones if excessive
- Most products combine these to balance the side effects
Serious side effects — call your doctor
Severe diarrhea or weakness with chronic high-dose use
Possible electrolyte disturbance — see your doctor.
Black stools NOT explained by other causes (some bismuth-containing antacids cause this)
Investigate to rule out bleeding.
Interactions
Antacids reduce absorption of MANY medications: thyroid hormones, antibiotics (tetracycline, fluoroquinolones), iron, calcium, certain blood thinners. Always separate from other medications by 2-4 hours.
Monitoring
No routine monitoring. Long-term high-dose use of calcium antacids: check serum calcium and kidney function. Avoid in advanced kidney disease (electrolyte issues).
Pregnancy & breastfeeding
Most antacids are safe in pregnancy. Calcium-based (Tums, Rennie) are often preferred. AVOID those containing aspirin (Alka-Seltzer) and bismuth (Pepto-Bismol) in pregnancy.
Questions to ask your doctor
Save this list or print it before your appointment — doctors appreciate prepared patients.
- Should I take antacid before or after meals?
- Is Gaviscon Advance better than regular Gaviscon?
- Can I take antacids during pregnancy?
Medically reviewed by: SGA Patient Education Panel · Last reviewed 24/04/2026