Is Magnesium Hydroxide Safe for Pregnancy? What Expecting Mothers Need to Know

October 10, 2025 •

4 min read

Constipation is a common issue affecting up to 44% of pregnant women in the second trimester. For relief, many turn to over-the-counter medications, prompting the question: is magnesium hydroxide safe for pregnancy? For occasional, short-term use, healthcare providers often consider it a generally safe option, but expert guidance is always necessary before taking any medication.

Quick Summary

Healthcare providers generally consider magnesium hydroxide safe for occasional use during pregnancy to relieve constipation or heartburn, but prefer it as a second-line treatment. Risks of high-dose, long-term use, especially in the third trimester, and potential for side effects necessitate medical consultation.

Key Points

Generally Safe for Short-Term Use: For occasional constipation or heartburn, magnesium hydroxide is typically considered safe by healthcare providers if used for short periods under medical supervision.
Risks of Prolonged Use: Long-term or high-dose use of magnesium hydroxide can lead to electrolyte imbalances and hypermagnesemia, which pose risks to both mother and baby.
Lifestyle Changes are First-Line: The safest and most recommended approach for managing constipation and heartburn in pregnancy is through lifestyle changes, including increased fiber intake, hydration, and moderate exercise.
Consult Your Doctor: Always talk to your healthcare provider before taking magnesium hydroxide or any other medication, even over-the-counter products, while pregnant.
Alternatives Available: For persistent constipation, bulk-forming agents (like Metamucil) or stool softeners (like Colace) are often preferred for their minimal systemic absorption.
Third-Trimester Caution: Some healthcare providers recommend avoiding magnesium-containing products in the final stages of pregnancy, especially in high doses, due to potential effects on uterine contractions.

Understanding Magnesium Hydroxide and Its Use in Pregnancy

Magnesium hydroxide is an over-the-counter medication that serves two primary purposes: as a laxative and as an antacid. As a saline laxative, it works by drawing water into the bowels, which helps soften stools and stimulate bowel movements, providing relief from occasional constipation. As an antacid, it neutralizes stomach acid to relieve heartburn and indigestion.

During pregnancy, hormonal changes and pressure from the growing uterus can slow down digestion, leading to common gastrointestinal issues like constipation and heartburn. Iron supplements, a vital part of prenatal nutrition, can also contribute to constipation. This makes finding effective and safe relief a priority for many expectant mothers.

Is Magnesium Hydroxide Safe for Pregnancy? The Medical Consensus

Most healthcare providers consider magnesium hydroxide, often known by the brand name Milk of Magnesia, to be generally safe for occasional use during pregnancy. It is minimally absorbed by the body, which reduces the risk of systemic effects on the developing fetus compared to other types of laxatives. However, the U.S. FDA has not formally assigned a pregnancy category, noting a lack of controlled human pregnancy data, which underscores the need for caution and medical supervision.

Important Considerations and Risks

While generally safe, magnesium hydroxide is not without risks, particularly with prolonged use or in high doses. Excess magnesium in the body can lead to a condition known as hypermagnesemia, which can cause serious health issues for both the mother and baby. Prolonged, high-dose use of magnesium has been associated with fetal bone abnormalities and other complications, especially in the third trimester. Therefore, it is strongly advised to only use it under the guidance of a healthcare provider and for a short duration.

Specific risks and concerns include:

Kidney problems: Women with kidney disease should avoid magnesium hydroxide, as their bodies may struggle to excrete excess magnesium.
Electrolyte imbalance: Long-term use can disrupt the body's electrolyte balance, which can lead to complications.
Third-trimester caution: Some healthcare providers recommend avoiding magnesium-containing products in the late stages of pregnancy, as high doses can potentially affect uterine contractions.

Comparison of Treatment Options for Constipation in Pregnancy

Choosing the right treatment for constipation depends on the severity of symptoms and medical advice. Lifestyle modifications are always the first-line approach, with medications reserved for cases where these changes are insufficient. Here is a comparison of common options:


Feature	Lifestyle Changes	Bulk-Forming Laxatives (e.g., Psyllium)	Osmotic Laxatives (e.g., Magnesium Hydroxide)
Primary Mechanism	Increased dietary fiber, water, and exercise to stimulate natural bowel function.	Absorbs water in the intestines to add bulk and soften stool.	Draws water into the bowels to soften stool and promote a bowel movement.
Systemic Absorption	Minimal to none.	Minimal to none, as they are not absorbed by the body.	Minimally absorbed, but systemic effects are possible with high doses.
Primary Safety Status	Safest option, recommended as first-line treatment.	Generally considered very safe for regular, long-term use.	Generally safe for short-term, occasional use under medical supervision.
Onset of Action	Gradual, over a few days.	Gradual, may take 12 to 72 hours.	Fast-acting, typically within 30 minutes to 6 hours.
Best Used For	Prevention and maintenance of regularity.	Long-term management of constipation.	Short-term, occasional constipation relief.
Key Side Effects	Bloating, gas if fiber is increased too quickly.	Gas, bloating, abdominal cramping.	Diarrhea, cramping, nausea, electrolyte imbalance with overuse.

Safe Alternatives and Management Strategies

Before reaching for a medication like magnesium hydroxide, expectant mothers should first explore natural and safer remedies for constipation and heartburn. Healthcare professionals almost universally recommend these as the primary course of action.

Lifestyle and Dietary Changes

Increase fiber intake: Aim for 25-30 grams of fiber per day from fruits, vegetables, beans, and whole grains. Prunes and prune juice are particularly effective.
Stay hydrated: Drink plenty of fluids, with water being the best choice, to keep stools soft.
Engage in moderate exercise: Activities like walking or swimming can help stimulate bowel movements.
Eat smaller, more frequent meals: This can help manage heartburn and prevent the digestive system from becoming overwhelmed.
Avoid trigger foods: Identify and limit foods that exacerbate heartburn, such as spicy or acidic foods.

Safe Over-the-Counter Options

If lifestyle adjustments are not enough, certain OTC options are often recommended as a safer, first-line medication choice during pregnancy:

Bulk-forming agents: Products containing psyllium (Metamucil) or polycarbophil (FiberCon) are excellent choices as they are not absorbed by the body.
Stool softeners: Docusate sodium (Colace) adds moisture to the stool, making it easier to pass.
Calcium carbonate antacids: Tums is a commonly recommended antacid for heartburn relief during pregnancy.

Conclusion

In summary, is magnesium hydroxide safe for pregnancy? For occasional, short-term relief of constipation or heartburn, it is generally considered safe when used under the guidance of a healthcare provider. However, risks exist, particularly with prolonged or high-dose usage, including potential electrolyte imbalances and complications related to excess magnesium. First-line treatments should always focus on lifestyle modifications like increasing fiber, water, and exercise. When medication is necessary, safer alternatives like bulk-forming laxatives or calcium carbonate antacids may be preferred, especially for long-term use. Ultimately, always consult your prenatal care provider before taking any over-the-counter medication to ensure the best and safest approach for you and your baby.

For more comprehensive information on pregnancy wellness and safe medication use, the American College of Obstetricians and Gynecologists (ACOG) is a highly recommended resource.

Frequently Asked Questions

Yes, many healthcare providers consider magnesium hydroxide safe for occasional, short-term use to treat constipation during pregnancy. However, it is crucial to first try dietary and lifestyle adjustments and to always consult your doctor before use.

Milk of Magnesia, a brand name for magnesium hydroxide, is generally considered safe for temporary use during pregnancy to address constipation or heartburn. It is vital to follow your doctor's advice on dosage and duration.

The main risks are associated with prolonged or high-dose use, which can cause electrolyte imbalances and, in rare cases, hypermagnesemia. These risks are higher for women with kidney problems.

Yes, bulk-forming laxatives like psyllium (Metamucil), stool softeners like docusate sodium (Colace), and osmotic laxatives like polyethylene glycol (Miralax) are often considered first-line medical options due to minimal absorption.

Yes, magnesium hydroxide acts as an antacid to relieve heartburn and is generally considered safe for occasional use. Calcium carbonate (Tums) is another widely recommended and often preferred option.

You should only take magnesium hydroxide under a doctor's supervision. Follow the recommended dosage on the label for occasional use and do not take it for longer than a week without medical advice.

While often used, some providers suggest caution with magnesium-containing products in the third trimester. High doses of magnesium sulfate (a related compound) have been linked to fetal bone issues and can affect labor contractions. Always seek specific guidance from your provider.

Natural remedies include increasing daily fiber intake from foods like fruits, vegetables, and whole grains, staying well-hydrated, and engaging in regular, moderate exercise.

Yes, magnesium can interfere with the absorption of certain nutrients and medications, including iron supplements commonly taken during pregnancy. It is essential to discuss all your medications and supplements with your doctor.