Sodium bicarbonate

Systemic alkalinizing agent, antacid

ATC code: B05XA02

Brand names: Alka-Seltzer

Updated 24 Sep 2026 · Methodology

Indications

Antacid therapy for mild dyspepsia

Third line

An effervescent bicarbonate tablet clears heartburn within minutes – that is how Alka-Seltzer and its relatives work. The AEMPS ficha técnica describes the indication narrowly: relief of heartburn and acid regurgitation in adults and adolescents from 12 years, one tablet after meals or when discomfort appears, at most 6 tablets a day. Then come caveats that other antacids do not have. The gas distends the stomach, belching brings acid back, and the ficha names the rebound effect directly among adverse reactions. The sodium load is noticeable for people with hypertension and a tendency to edema. The tablet is not taken right after a heavy meal and drinking: carbon dioxide released into a full stomach has in rare cases led to perforation of the wall. If heartburn lasts beyond 14 days, an examination is needed rather than the next pack.

Sources

ICD-10: K30 · ICD-11: DD90.3

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

Gastroesophageal reflux disease

Not recommended

A spoon of baking soda in a glass of water is the best known home remedy for heartburn, and it works exactly once. In reflux disease soda is unsuitable as ongoing treatment. Acid neutralization lasts minutes, then the stomach answers with a new release – the AEMPS ficha técnica lists the rebound effect among adverse reactions. Sodium from soda retains water, and for people with hypertension and heart failure that costs more than the heartburn did. guideline CG184 builds reflux management differently: a course of a proton pump inhibitor, assessment of alarm symptoms, gastroscopy where needed, with antacids and alginates on top for fast relief. If soda or effervescent bicarbonate is advised daily for heartburn, consider seeking a second opinion.

Sources

ICD-10: K21 · ICD-11: DA22

Body detoxification and cleansing

Not recommended

Soda is sold as a way to «alkalinize the body»: an alkaline diet, alkaline water, soda on an empty stomach – with a promise that tumours do not grow in an alkaline environment. The systematic review by Fenton and Huang (BMJ Open 2016) looked for a link between dietary acid load, alkaline water and cancer and found not a single study supporting it. Biology does not allow it either: blood pH is held between 7.35 and 7.45 by buffer systems, the lungs and the kidneys, and drinking soda does not shift it. Something else does shift: soda easily produces metabolic alkalosis, sodium retention, edema and hypokalemia, and ruptures of the stomach wall are described on a full stomach. If soda was recommended as a course for alkalinizing or cancer prevention, consider seeking a second opinion.

Sources

How to read tiers A–F

AStrong evidence – first or second line in international guidelines
BRecommended in selected cases
CStudy data contradict each other
DBenefit not proven, no documented harm
FDocumented harm, or risk without benefit

Mechanism of action

Sodium bicarbonate neutralizes gastric hydrochloric acid instantly, and the reaction products are sodium chloride, water and carbon dioxide. The gas creates the main quirk: the stomach distends, belching follows and part of the acid comes back with it. In effervescent tablets such as Alka-Seltzer the bicarbonate comes with citric acid, the reaction yields sodium citrate, and together with the remaining bicarbonate it acts as a buffer. Unlike insoluble antacids, bicarbonate is absorbed, so it also acts systemically: it alkalinizes blood and urine, while sodium retains water. From this grow the contraindications in the AEMPS ficha técnica – metabolic and respiratory alkalosis, a tendency to edema, hypocalcemia, hypochlorhydria.

Safety

Contraindications

Hypersensitivity to sodium bicarbonate
Metabolic or respiratory alkalosis
Hypocalcemia
Hypochlorhydria
Tendency to edema
Appendicitis or its symptoms
Bowel obstruction

Serious adverse effects

Metabolic alkalosis
Sodium and water retention with edema, rise in blood pressure
Hypokalemia
Gastric perforation when taken on an overfull stomach

Common adverse effects

Bloating
Belching
Acid rebound
Nausea

Pregnancy: can you take Sodium bicarbonate?

Data on sodium bicarbonate in pregnancy are limited. The ficha técnica advises against it in pregnancy: the product increases fluid retention and may cause metabolic alkalosis in mother or fetus.

Breastfeeding: can you take Sodium bicarbonate?

Data on sodium bicarbonate passing into breast milk are limited, so it is not recommended during breastfeeding.

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

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Frequently asked

What is Sodium bicarbonate used for?

Sodium bicarbonate is evaluated for the following indications with varying evidence strength: Antacid therapy for mild dyspepsia (evidence tier C), Gastroesophageal reflux disease (evidence tier D), Body detoxification and cleansing (evidence tier F). See the full indication matrix with dosing and citations above on this page.

What are the side effects of Sodium bicarbonate?

Common side effects of Sodium bicarbonate (≥ 1 in 100): Bloating, Belching, Acid rebound, Nausea. See the Safety section for uncommon and serious reactions.

Is Sodium bicarbonate safe during pregnancy?

Data on sodium bicarbonate in pregnancy are limited. The ficha técnica advises against it in pregnancy: the product increases fluid retention and may cause metabolic alkalosis in mother or fetus.

Is Sodium bicarbonate compatible with breastfeeding?

Data on sodium bicarbonate passing into breast milk are limited, so it is not recommended during breastfeeding.

Who should not take Sodium bicarbonate?

Sodium bicarbonate is contraindicated in: Hypersensitivity to sodium bicarbonate; Metabolic or respiratory alkalosis; Hypocalcemia; Hypochlorhydria; Tendency to edema. Full list in the Safety section.

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