Does Allegra interact with antacids?
Short answer
Medication question
Yes, certain antacids can interfere with Allegra. Products containing aluminum or magnesium — like Maalox or Mylanta — can bind to fexofenadine in the gut and reduce how much is absorbed. The fix is simple: space Allegra and those antacids by about two hours. Tums (calcium carbonate) does not appear to have the same effect.
This is a general research summary, not medical advice. A pharmacist can confirm it for your situation.
Key facts
The Allegra prescribing information specifically warns that aluminum and magnesium-containing antacids can reduce fexofenadine absorption.
Separating Allegra from aluminum/magnesium antacids by two hours is the recommended strategy to avoid this interaction.
Calcium carbonate antacids (Tums) do not share the same documented interaction with fexofenadine.
Here's the nuance
A one-liner rarely tells the whole story. This is the honest detail behind the short answer above.
Allegra (fexofenadine) can have its absorption reduced when taken alongside antacids that contain aluminum hydroxide or magnesium hydroxide. The mechanism is a physical one: these compounds can interact with fexofenadine in the gastrointestinal tract and reduce how much of the drug is available for absorption. The Allegra prescribing information specifically notes this interaction.
The practical solution is straightforward — separate your Allegra dose from any aluminum or magnesium-containing antacid by approximately two hours. Taking one before the other, with that buffer, removes most of the concern. Common antacid brands in this category include Maalox and Mylanta, though formulations vary, so it's worth checking the ingredient list.
Calcium carbonate antacids — Tums being the most recognizable — do not appear to cause the same reduction in fexofenadine absorption. If you take an antacid regularly and use Allegra daily, switching to a calcium-only product (where appropriate for your situation) can simplify the timing.
This is a known, manageable interaction — not a dangerous one. The consequence of missing the spacing is potentially less allergy relief, not a serious adverse event. That said, if you're on multiple medications or an antacid for a chronic condition, your pharmacist can help you sequence your doses so everything works as intended.
The key points
The handful of things that decide the answer — skim these if you only read one section.
Aluminum and magnesium antacids are the ones to separate
Products like Maalox and Mylanta contain these compounds, which can bind fexofenadine in the gut and reduce absorption. The Allegra label specifically calls this out.
Space them two hours apart
Taking Allegra two hours before or after an aluminum or magnesium antacid largely resolves the interaction. Check the label of your specific antacid for its active ingredients.
Calcium-only antacids (Tums) are less of a concern
Calcium carbonate does not appear to interact with fexofenadine in the same way. If you use antacids regularly, this may be a simpler option — confirm with your pharmacist.
The consequence is reduced efficacy, not danger
Taking them together isn't dangerous — the main risk is that Allegra may be less effective at controlling your allergy symptoms that day.
Pharmacist can map out your schedule
If you take several medications and antacids regularly, a pharmacist can build a simple dosing schedule so everything is properly spaced.
Please read before acting on this
General information — not medical advice
This page is a general research summary about the medication in question. It does not account for your specific health, other medicines you take, or your dose, and it can go out of date. It is not medical advice, a prescription, or a substitute for professional judgment.
Ask your pharmacist or prescriber before starting, stopping, changing, or continuing any medication — they can check it against your situation in minutes.
❓Frequently Asked Questions
Tums (calcium carbonate) does not appear to interact with Allegra in the same way that aluminum or magnesium-based antacids do, so taking them together is generally considered less of a concern. However, if you take any supplements or antacids at the same time as Allegra regularly, it's worth mentioning it to a pharmacist to confirm no issues with your specific products.
Antacids containing aluminum hydroxide or magnesium hydroxide are the ones to watch. Common examples include Maalox and Mylanta. These can reduce fexofenadine absorption when taken simultaneously. The solution is to separate them by about two hours rather than avoid them entirely. Check the active ingredients on your antacid's label to know which type you have.
Pepcid (famotidine) is an H2 blocker, and Prilosec (omeprazole) is a proton pump inhibitor — neither is an aluminum or magnesium antacid, so they don't have the same documented absorption interaction with fexofenadine. That said, any combination of medications can have nuances, and a pharmacist is the right person to confirm whether your specific combination is safe and well-timed.
Aluminum and magnesium compounds in antacids can bind to fexofenadine molecules in the gastrointestinal tract, reducing the amount that passes through the gut wall into the bloodstream. It's a physical interaction in the digestive system rather than a liver or kidney metabolism issue. Taking the two medications far enough apart — about two hours — allows Allegra to be absorbed before the antacid is present in the gut.
Reviewed by
Dr. Chet TharpeMD
Last reviewed July 2026
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This content is for general informational purposes only. It is not medical advice, a prescription, or a substitute for professional judgment, and it does not account for your health, other medications, or dose. Always ask your pharmacist or prescriber before starting, stopping, or changing any medication.