What does the research show about antacids and alginates?

Antacids and alginates

A meta-analysis found plain antacids gave a small, borderline gain in heartburn relief over placebo. Alginate-antacid combinations relieved reflux more than placebo or antacids in two meta-analyses, not in a third pooled estimate. In pregnancy, an antacid relieved heartburn more than placebo. Heavy calcium carbonate use caused milk-alkali syndrome, and antacids blocked levothyroxine and ciprofloxacin absorption.

Add to Bio HackChecked 2026-11-14

Status: Sold over the counter in the US as antacids for heartburn, acid indigestion, sour stomach and upset stomach, under FDA's OTC monograph, for adults and children 12 and older. US Gaviscon lists aluminum hydroxide and magnesium carbonate as its active ingredients and alginic acid as an inactive one. Most alginate trials tested UK formulations with sodium alginate as an active ingredient.
Also called: antacids, calcium carbonate, Tums, magnesium hydroxide, milk of magnesia, aluminum hydroxide, magnesium carbonate, Maalox, Mylanta, Rolaids, Gaviscon, Gaviscon Extra Strength, Gaviscon Advance, Gaviscon Double Action, alginate, sodium alginate, alginic acid, raft-forming antacid, heartburn tablets
Taken for: heartburn, acid reflux, GERD, indigestion, sour stomach, upset stomach, heartburn in pregnancy, stomach ulcers

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help3

ModerateOne meta-analysis found antacids gave a small, borderline gain in heartburn relief over placebo, 8 percentage points, and less need for rescue tablets.
ModerateShown in two small trials to relieve heartburn in pregnancy completely more often than placebo or no treatment. An alginate and a magnesium-aluminum antacid did not differ.
LimitedOne 1977 trial found a large-dose antacid regimen healed duodenal ulcers more often than placebo, 28 of 36 against 17 of 38, without better symptom relief.

Reported risks6

LimitedCase series: milk-alkali syndrome caused 8.8% of high blood calcium in hospital patients without end-stage kidney disease, and a quarter of the severe cases.How often is not known
LimitedCase reports: long-term heavy use of aluminum hydroxide antacids caused phosphate depletion and osteomalacia, with stress fractures, which improved after stopping them.How often is not known
LimitedThe labels ask people with kidney disease or a magnesium-restricted diet to consult a doctor before magnesium antacids, and Gaviscon adds sodium-restricted diets.How often is not known
LimitedOne study found calcium carbonate taken with levothyroxine lowered free T4 and raised TSH, from 1.6 to 2.7 mIU/L, reversing after calcium was stopped.How often is not known
LimitedThe ciprofloxacin label states magnesium and aluminum antacids and calcium lower its absorption. Antacid labels warn they may interact with certain prescription drugs.How often is not known
LimitedFDA warns that antacid products containing aspirin can cause stomach or intestinal bleeding, with serious cases found in its reports despite a 2009 warning.How often is not known

What people take it for, and what was found

Shown to help3

Moderate

Heartburn relief, plain antacids

One meta-analysis found antacids gave a small, borderline gain in heartburn relief over placebo, 8 percentage points, and less need for rescue tablets.

Compared with placebo [1]

The numbers and sources

Effect: Across 4 placebo-controlled trials, antacids showed a trend toward symptom improvement, with an absolute benefit increase of 8% (95% CI 0 to 16%), and lowered the need for rescue antacids (OR 0.70, 95% CI 0.59 to 0.84). Placebo response across the trials in the review ranged from 37% to 64% [1].
Population: 578 people on antacids and 577 on placebo with reflux symptoms, in trials from 1972 to 2005 [1].
Sources: [1]
Caveats: One meta-analysis of four trials. The lower confidence limit of the main estimate touched no effect [1].

ModerateStudied in pregnancy

Heartburn in pregnancy

Shown in two small trials to relieve heartburn in pregnancy completely more often than placebo or no treatment. An alginate and a magnesium-aluminum antacid did not differ.

Compared with placebo or no treatment [5]; magnesium and aluminum antacid gel [6]

The numbers and sources

Effect: Complete heartburn relief was more frequent on drug treatment than on placebo or no treatment (RR 1.85, 95% CI 1.36 to 2.50, 2 trials, 256 women, moderate quality). One of the two trials tested magnesium and aluminum hydroxide with simethicone, the other intramuscular prostigmine [5]. Over 2 weeks, heartburn frequency improved in 80% on an alginate and 88% on a magnesium-aluminum antacid gel, with no difference in intensity, quality of life or side effects [6].
Population: 9 trials with 725 pregnant women, 4 contributing data on 358 [5]; 100 pregnant women under 36 weeks with heartburn at least twice a week [6].
Sources: [5], [6]
Caveats: Small trials of mixed risk of bias, and one of the pooled two used a drug rarely given now [5].

Limited

Duodenal ulcer healing

One 1977 trial found a large-dose antacid regimen healed duodenal ulcers more often than placebo, 28 of 36 against 17 of 38, without better symptom relief.

Compared with placebo [7]

The numbers and sources

Effect: After 28 days, ulcers healed completely in 28 of 36 people on the antacid regimen and 17 of 38 on an inert placebo. Ulcer symptoms did not improve more than on placebo, and symptoms in week 4 poorly predicted whether an ulcer remained [7].
Population: 74 adults with duodenal ulcers confirmed by endoscopy, in a double-blind trial [7].
Sources: [7]
Caveats: One trial of a large-dose regimen, published before the role of H. pylori in ulcers was known [7].

Mixed results1

Moderate

Reflux symptoms, alginate-antacid combinations

Mixed results: two meta-analyses found alginate combinations relieved reflux symptoms more than placebo or antacids, while a third found no significant pooled difference.

Compared with placebo [1][2]; placebo or antacids [3][4]

The numbers and sources

Effect: Across 4 trials, alginate-antacid combinations improved symptoms more than placebo, an absolute benefit increase of 26% (95% CI 12 to 41%) [1]. Across 14 trials, alginates raised the odds of symptom resolution against placebo or antacids (OR 4.42, 95% CI 2.45 to 7.97, I² 71%) [3]. A review of trials from 2000 to 2020 found better outcomes in a qualitative look at four trials, but its pooled analysis found no significant difference from placebo or antacids for heartburn, regurgitation or dyspepsia [4]. In a 7-day trial, 47.8% on Gaviscon Double Action tablets and 33.2% on placebo had a clinically important drop in reflux score (OR 1.85, 95% CI 1.23 to 2.78) [2].
Population: 146 people on alginate-antacid and 138 on placebo [1]; 2,095 adults in 14 trials [3]; 11 randomized trials [4]; 424 adults with reflux symptoms [2].
Sources: [1], [3], [4], [2]
Caveats: Heterogeneity was high in [3]. The 2019 trial's first author was employed by the product's maker [2].

Not shown to help2

Moderate

Alginates compared with acid-reducing drugs

Not shown to differ from proton pump inhibitors or H2 blockers for reflux symptoms in pooled trials, with a nonsignificant lean toward the acid reducers.

Compared with proton pump inhibitors or H2 blockers [3]; proton pump inhibitors [4]

The numbers and sources

Effect: Against proton pump inhibitors or H2 blockers, alginates had lower odds of symptom resolution, a difference that was not significant (OR 0.58, 95% CI 0.27 to 1.22) [3]. A second review found no difference between alginates and proton pump inhibitors in a descriptive analysis, and adding an alginate to a proton pump inhibitor did not change heartburn, regurgitation or dyspepsia [4].
Population: Adults with reflux symptoms in randomized trials [3][4].
Sources: [3], [4]
Caveats: Few head-to-head trials, and the second review did not pool them [4]. Proton pump inhibitors and H2 blockers have their own pages.

Limited

Indigestion without an ulcer

One trial in non-ulcer dyspepsia found an antacid suspension reduced stomach pain no more than placebo over 3 weeks, at most 4 percentage points more.

Compared with placebo and cimetidine [8]

The numbers and sources

Effect: Pain intensity fell 25% on placebo, and neither antacid nor cimetidine gave more than a 4% better effect. Pain scores on the active drugs followed placebo closely, with no significant difference at any stage [8].
Population: 159 adults with chronic or recurrent upper abdominal pain and no organic disease, in a double-blind, double-dummy trial [8].
Sources: [8]
Caveats: One trial [8].

Doses studied

The pooled heartburn trials and the alginate meta-analyses do not give doses in their abstracts [1][3][4]. The Gaviscon Double Action trial gave tablets for 7 days [2]. The ulcer trial used a large-dose antacid regimen for 28 days [7], and the dyspepsia trial an antacid suspension 1 and 3 hours after meals for 3 weeks [8]. The levothyroxine interaction study used 1,200 mg of elemental calcium a day as calcium carbonate for 3 months [9]. Tums EX holds 750 mg of calcium carbonate per tablet, with no more than 10 tablets in 24 hours, or 6 in pregnancy, and no use of the maximum for more than 2 weeks [10]. Rolaids Original holds calcium carbonate 675 mg and magnesium hydroxide 135 mg per tablet, up to 10 a day [11]. Mylanta Maximum Strength holds aluminum hydroxide 800 mg, magnesium hydroxide 800 mg and simethicone 80 mg per 10 mL, up to 60 mL a day [12]. Gaviscon Extra Strength holds aluminum hydroxide 160 mg and magnesium carbonate 105 mg per tablet, 2 to 4 tablets four times a day, up to 16 [13].

Risks

Reported risks6

LimitedHow often is not known

High calcium from calcium carbonate (milk-alkali syndrome)

Case series: milk-alkali syndrome caused 8.8% of high blood calcium in hospital patients without end-stage kidney disease, and a quarter of the severe cases.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Of 125 inpatients with high blood calcium, 11 (8.8%) had milk-alkali syndrome, the third leading cause after malignancy and hyperparathyroidism. Among 35 with severe high calcium, 9 (25.7%) had milk-alkali syndrome, the second leading cause. Chronic kidney disease, diuretic use, vitamin D supplements and upper gut disease were common among them [14].
Population: 125 hospitalized adults with high blood calcium at one US university hospital, 1998 to 2003 [14].
Sources: [14]
Caveats: A chart review that gives no rate among people who take calcium carbonate [14].

LimitedHow often is not known

Phosphate loss and bone softening with aluminum antacids

Case reports: long-term heavy use of aluminum hydroxide antacids caused phosphate depletion and osteomalacia, with stress fractures, which improved after stopping them.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: A woman who took a high-dose aluminum and magnesium hydroxide antacid for 8 years, within label directions, developed severe osteomalacia from phosphate depletion, with aluminum deposits on 27.6% of bone surface despite normal kidney function. Bone density rose after stopping the antacid and taking phosphate, calcium and vitamin D [15]. A man with long-term aluminum hydroxide use had bone pain, multiple stress fractures and osteomalacia, which healed after withdrawal and calcium and phosphorus [16].
Population: Single case reports, a 39-year-old woman [15] and a 53-year-old man [16].
Sources: [15], [16]
Caveats: Case reports give no rate [15][16].

LimitedHow often is not known

Conditions the labels name

The labels ask people with kidney disease or a magnesium-restricted diet to consult a doctor before magnesium antacids, and Gaviscon adds sodium-restricted diets.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: The Mylanta and Rolaids labels list kidney disease and a magnesium-restricted diet as reasons to ask a doctor first, and Mylanta Maximum Strength holds 340 mg of magnesium per 10 mL dose [12][11]. The Gaviscon label asks people on a sodium-restricted diet to ask first, with 20 mg of sodium per tablet [13]. The labels say not to use the maximum dose for more than 2 weeks [10][11][12][13].
Population: Labeling statements [10][11][12][13].
Sources: [10], [11], [12], [13]
Caveats: No rate is given.

LimitedHow often is not known

Lower levothyroxine absorption

One study found calcium carbonate taken with levothyroxine lowered free T4 and raised TSH, from 1.6 to 2.7 mIU/L, reversing after calcium was stopped.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Taking 1,200 mg a day of calcium as calcium carbonate with levothyroxine lowered mean free T4 from 17 to 15 pmol/L and total T4 from 118 to 111 nmol/L. Mean TSH rose from 1.6 to 2.7 mIU/L, and 20% had TSH above the normal range, highest 7.8 mIU/L. Levels returned after calcium was stopped [9]. The Synthroid label says to take levothyroxine at least 4 hours apart from calcium carbonate [17].
Population: 20 adults aged 27 to 78 with hypothyroidism on stable levothyroxine, 11 men, followed over 3 months [9].
Sources: [9], [17]
Caveats: A small study without a control group [9].

LimitedHow often is not known

Lower ciprofloxacin absorption and other prescription drugs

The ciprofloxacin label states magnesium and aluminum antacids and calcium lower its absorption. Antacid labels warn they may interact with certain prescription drugs.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: The ciprofloxacin label directs it to be taken at least 2 hours before or 6 hours after magnesium or aluminum antacids and products containing calcium, iron or zinc, which decrease its absorption [18]. The Tums, Rolaids, Mylanta and Gaviscon labels ask people taking a prescription drug to consult a doctor or pharmacist, stating antacids may interact with certain prescription drugs [10][11][12][13].
Population: Labeling statements [18][10][11][12][13].
Sources: [18], [10], [11], [12], [13]
Caveats: No rate is given.

LimitedHow often is not known

Bleeding with aspirin-containing antacids

FDA warns that antacid products containing aspirin can cause stomach or intestinal bleeding, with serious cases found in its reports despite a 2009 warning.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: FDA states aspirin-containing medicines for heartburn, sour stomach, acid indigestion or upset stomach can cause stomach or intestinal bleeding. It found new cases of serious bleeding in its adverse event database, some needing transfusion. Risk is higher at age 60 or older, with past ulcers or bleeding, with blood thinners, steroids or other NSAIDs, and with 3 or more drinks a day [19].
Population: FDA review of adverse event reports [19].
Sources: [19]
Caveats: FDA calls the cases rare but gives no rate. This applies only to products that contain aspirin [19].

Checked, no increase found1

Moderate

Side effects in trials

Not linked to more side effects than placebo in pooled trials of alginates and of antacids in pregnancy. A large-dose ulcer regimen caused mild diarrhea.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Adverse events and withdrawals did not differ between alginates and placebo or proton pump inhibitors [4]. In pregnancy, side effects did not clearly differ between drug treatment and placebo or no treatment (RR 0.63, 95% CI 0.21 to 1.89, very low quality) [5]. In the ulcer trial, mild diarrhea was the only side effect seen on the large-dose antacid regimen [7].
Population: 11 randomized trials [4]; 256 pregnant women in 2 trials [5]; 74 adults with duodenal ulcers [7].
Sources: [4], [5], [7]
Caveats: Small, short trials [5]. The pregnancy trials reported no outcomes for babies, such as birth defects or birth weight [5].

Claims tested and not found

That antacids ease indigestion when there is no ulcer. In 159 people with non-ulcer dyspepsia, pain fell no more on an antacid than on placebo over 3 weeks [8].
That ulcer pain tracks whether an ulcer has healed on antacids. Symptoms did not improve more than on placebo, and symptoms in week 4 poorly predicted whether an ulcer remained [7].

Sources

Tran T, Lowry AM, El-Serag HB. Meta-analysis: the efficacy of over-the-counter gastro-oesophageal reflux disease therapies. Alimentary Pharmacology & Therapeutics. 2007. https://doi.org/10.1111/j.1365-2036.2006.03135.x
Wilkinson J, Wade A, Thomas SJ, et al. Randomized clinical trial: a double-blind, placebo-controlled study to assess the clinical efficacy and safety of alginate-antacid (Gaviscon Double Action) chewable tablets in patients with gastro-oesophageal reflux disease. European Journal of Gastroenterology & Hepatology. 2019. https://doi.org/10.1097/meg.0000000000001258
Leiman DA, Riff BP, Morgan S, et al. Alginate therapy is effective treatment for GERD symptoms: a systematic review and meta-analysis. Diseases of the Esophagus. 2017. https://doi.org/10.1093/dote/dow020
Zhao CX, Wang JW, Gong M. Efficacy and safety of alginate formulations in patients with gastroesophageal reflux disease: a systematic review and meta-analysis of randomized controlled trials. European Review for Medical and Pharmacological Sciences. 2020. https://pubmed.ncbi.nlm.nih.gov/33275256/
Phupong V, Hanprasertpong T. Interventions for heartburn in pregnancy. Cochrane Database of Systematic Reviews. 2015. https://doi.org/10.1002/14651858.cd011379.pub2
Meteerattanapipat P, Phupong V. Efficacy of alginate-based reflux suppressant and magnesium-aluminium antacid gel for treatment of heartburn in pregnancy: a randomized double-blind controlled trial. Scientific Reports. 2017. https://doi.org/10.1038/srep44830
Peterson WL, Sturdevant RA, Frankl HD, et al. Healing of duodenal ulcer with an antacid regimen. New England Journal of Medicine. 1977. https://doi.org/10.1056/nejm197708182970701
Nyrén O, Adami HO, Bates S, et al. Absence of therapeutic benefit from antacids or cimetidine in non-ulcer dyspepsia. New England Journal of Medicine. 1986. https://doi.org/10.1056/nejm198602063140603
Singh N, Singh PN, Hershman JM. Effect of calcium carbonate on the absorption of levothyroxine. JAMA. 2000. https://doi.org/10.1001/jama.283.21.2822
U.S. Food and Drug Administration. TUMS EX (calcium carbonate) tablet, drug facts label. 2026. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=593a0494-d669-4bcf-8412-b92645b2d76c
U.S. Food and Drug Administration. ROLAIDS ORIGINAL (calcium carbonate and magnesium hydroxide) chewable tablet, drug facts label. 2026. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=28d9b359-ae44-2c87-e063-6394a90a22f0
U.S. Food and Drug Administration. MYLANTA MAXIMUM STRENGTH (aluminum hydroxide, magnesium hydroxide and simethicone) suspension, drug facts label. 2024. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=56853b20-a2aa-4b19-a428-3dde232114c6
U.S. Food and Drug Administration. GAVISCON EXTRA STRENGTH (aluminum hydroxide and magnesium carbonate) chewable tablet, drug facts label. 2025. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7f367927-c366-465c-a059-e2cfb337d562
Picolos MK, Lavis VR, Orlander PR. Milk-alkali syndrome is a major cause of hypercalcaemia among non-end-stage renal disease (non-ESRD) inpatients. Clinical Endocrinology. 2005. https://doi.org/10.1111/j.1365-2265.2005.02383.x
Woodson GC. An interesting case of osteomalacia due to antacid use associated with stainable bone aluminum in a patient with normal renal function. Bone. 1998. https://doi.org/10.1016/s8756-3282(98)00060-x
Carmichael KA, Fallon MD, Dalinka M, et al. Osteomalacia and osteitis fibrosa in a man ingesting aluminum hydroxide antacid. American Journal of Medicine. 1984. https://doi.org/10.1016/0002-9343(84)90871-4
U.S. Food and Drug Administration. SYNTHROID (levothyroxine sodium) tablet, prescribing information. 2024. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1e11ad30-1041-4520-10b0-8f9d30d30fcc
U.S. Food and Drug Administration. CIPROFLOXACIN tablet, prescribing information. 2026. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=74e2dd24-5c6e-4dde-a2ab-f2d2e61734d8
U.S. Food and Drug Administration. Warning: Aspirin-Containing Antacid Medicines Can Cause Bleeding. Consumer Update. Accessed 2026. https://www.fda.gov/consumers/consumer-updates/warning-aspirin-containing-antacid-medicines-can-cause-bleeding

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