Aluminum Hydroxide/Magnesium Hydroxide Side Effects: What to Expect and When to Call Your Doctor

Aluminum hydroxide and magnesium hydroxide antacids are among the most commonly used OTC products in the world, and most people tolerate them well. But like any medication, they can cause side effects — especially when used frequently or in larger amounts than directed. This guide covers what to expect, what to watch for, and when to contact your healthcare provider.

Common Side Effects of Aluminum Hydroxide/Magnesium Hydroxide

Most people who use this antacid as directed experience few or no side effects. When side effects do occur, the most common are related to the effects of aluminum and magnesium on the gastrointestinal (GI) tract:

• Constipation: Caused by the aluminum hydroxide component. Drinking more water and eating fiber-rich foods can help minimize this.
• Diarrhea or loose stools: Caused by the magnesium hydroxide component. The two effects often balance out in the combination product.
• Nausea: Mild stomach discomfort can occasionally occur, especially if the antacid is taken on a very empty stomach.

Serious Side Effects: When to Call Your Doctor Immediately

Stop using aluminum hydroxide/magnesium hydroxide and seek medical attention right away if you experience any of these serious side effects:

• Signs of hypermagnesemia (high magnesium): Confusion, drowsiness, facial flushing, sweating, muscle weakness, fast or irregular heartbeat, difficulty breathing. This is most likely to occur in people with kidney disease taking large amounts of this antacid.
• Signs of hypophosphatemia (low phosphate): Loss of appetite, general weakness, bone pain, muscle cramps. This can occur with prolonged use because aluminum hydroxide binds phosphate in the GI tract and reduces its absorption.
• Allergic reaction: Skin rash, itching, hives, swelling of the face, lips, tongue, or throat. Seek emergency care immediately.
• Serious neurological symptoms: Severe confusion, slurred speech, tremors, or sudden vision changes. These are rare but require immediate attention.

Who Is at Higher Risk for Side Effects?

Certain groups are at greater risk of experiencing serious side effects from aluminum hydroxide/magnesium hydroxide:

• People with kidney disease: The kidneys clear magnesium from the body. With reduced kidney function, magnesium can accumulate and reach toxic levels (hypermagnesemia). Similarly, aluminum can accumulate, causing bone disease and neurological problems.
• People using antacids daily for more than 2 weeks: Prolonged use can lead to hypophosphatemia (low phosphate), osteomalacia (softening of the bones), and potential aluminum toxicity.
• Pregnant people: Aluminum hydroxide is not recommended during pregnancy due to potential effects on calcium metabolism. Consult an OB-GYN before using any antacid while pregnant.
• Children under 12: Should not use without medical advice. Dosing in children must be physician-directed.

Does Aluminum Hydroxide/Magnesium Hydroxide Affect Other Medications?

Yes — this is one of the most important safety considerations. Aluminum hydroxide/magnesium hydroxide can significantly reduce the absorption of many medications taken by mouth. There are 445 documented drug interactions. The most important ones:

• Fluoroquinolone antibiotics (ciprofloxacin, levofloxacin) — separate by 2 hours
• Tetracycline antibiotics (doxycycline, minocycline) — separate by 2 hours
• Levothyroxine (Synthroid) — separate by 4 hours
• Iron supplements (ferrous sulfate) — separate by 2 hours
• Aspirin — may increase aluminum absorption; discuss with your pharmacist

The general rule: take all other oral medications at least 2 hours before or 2 hours after taking an antacid.

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Safe Use Guidelines

To minimize side effects and use this antacid safely:

1. Do not take for more than 2 consecutive weeks without physician guidance
2. Don't exceed the maximum dose stated on the package
3. Drink adequate water throughout the day, especially if you tend toward constipation
4. Separate from other medications by at least 2 hours
5. If you have kidney disease, consult your doctor before use

Finding This Medication at a Pharmacy Near You

If you're having trouble finding aluminum hydroxide/magnesium hydroxide at your local pharmacy, medfinder can call pharmacies near you to find which ones have it in stock. For more information on drug interactions, see our dedicated guide on aluminum hydroxide/magnesium hydroxide drug interactions.