What Blocks Your Thyroid Hormone from Working — and What to Do About It

If you’re taking thyroid hormone—whether it’s for hypothyroidism, Hashimoto’s, or another thyroid condition—it’s essential to know that certain common supplements and medications can block your body from absorbing it properly. Even if you're taking the right dose, your thyroid levels might still look off simply because something else is getting in the way.

Supplements & Medications That Block Thyroid Hormone Absorption

For those of you on thyroid hormone, here are the top culprits that interfere with thyroid hormone absorption:

1. Iron supplements

Iron can bind to thyroid medication in the digestive tract and make it unavailable to your body. This is a common issue for those also treating anemia or low ferritin levels.

2. Sucralfate (Carafate)

Often used to treat ulcers or digestive irritation, this medication creates a protective coating on the stomach lining—but it also blocks thyroid hormone from being absorbed.

3. Calcium carbonate

This form of calcium is found in many over-the-counter supplements and antacids. Most people in the U.S. don’t need calcium supplements in the first place, and this type specifically can significantly hinder thyroid medication.

4. Aluminum-containing antacids

Brands like Maalox and Mylanta fall into this category. They may bring temporary relief from indigestion, but they interfere with your thyroid treatment.

5. Cholestyramine (Questran)

Used to lower cholesterol or as part of treatment for mold toxicity, cholestyramine binds to various substances in the gut—including your thyroid hormone.

6. Raloxifene (Evista)

Sometimes prescribed to treat osteoporosis or reduce breast cancer risk, this medication can also block absorption of thyroid hormone.

7. Proton-pump inhibitors (PPIs)

These include drugs like omeprazole (Prilosec), esomeprazole (Nexium), and lansoprazole (Prevacid).

Personally, I find these medications too toxic for long-term use. They may offer short-term relief from acid reflux or GERD, but over time, they can cause more harm than good. They’re also quite addictive. I usually recommend tapering off PPIs and switching to famotidine (Pepcid), which is significantly safer in the short term.

Even better, I guide people through a natural regimen to heal the underlying indigestion, so they can eventually wean off Pepcid too.

Timing Is Everything

To ensure proper absorption of your thyroid medication, it’s generally advised to wait at least 4 hours between taking your thyroid pill and any of the substances listed above—especially iron, calcium, or antacids.

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