Updated: January 27, 2026

Westhroid Drug Interactions: What to Avoid and What to Tell Your Doctor

Author

Peter Daggett

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Medications That Reduce Westhroid Absorption
Medications Whose Effects Are Altered by Westhroid
Medications That Affect Thyroid Hormone Levels
Food and Supplement Interactions
What to Tell Your Doctor Before Starting Westhroid

Westhroid interacts with several common medications and supplements. Here's what to avoid, what to separate by 4 hours, and what your doctor needs to know before you start.

Westhroid interacts with a number of common medications, supplements, and foods. Some interactions affect how much Westhroid your body absorbs, while others can cause serious side effects if not managed. Here's a clear guide to what you need to know.

Medications That Reduce Westhroid Absorption

These medications bind to thyroid hormones in the gut and prevent them from being absorbed. The solution is simple: take them at least 4 hours before or after your Westhroid dose.

— bile acid sequestrants used for high cholesterol; significantly reduce T4/T3 absorption. Separate by 4+ hours.

— including Tums and most OTC antacids. Separate by 4 hours.

— very commonly taken and significantly reduces thyroid hormone absorption. Separate by 4 hours.

— used for stomach ulcers. Separate by 4 hours.

— may reduce absorption by altering stomach acidity; some patients need higher Westhroid doses while on PPIs.

— weight loss medication; reduces absorption of thyroid hormones. Separate by 4 hours.

Medications Whose Effects Are Altered by Westhroid

Thyroid hormones affect the way your body processes other medications—meaning Westhroid can make these drugs more or less effective:

— MAJOR interaction. Westhroid increases warfarin's anticoagulant (blood-thinning) effect, which can raise bleeding risk. Your INR (blood clotting level) must be monitored closely when starting, stopping, or changing Westhroid dose.

— thyroid hormone affects glucose metabolism, so starting Westhroid can alter blood sugar control. Monitor blood sugar closely and be prepared for insulin dose adjustments.

— thyroid hormones can affect digoxin levels in the blood; monitoring may be needed.

— thyroid hormones may enhance the effect of tricyclic antidepressants, potentially increasing both therapeutic effects and side effects.

Medications That Affect Thyroid Hormone Levels

These drugs can change thyroid hormone binding proteins in the blood, affecting how much free T3 and T4 is available:

— increase thyroid-binding globulin (TBG), which means you may need a higher Westhroid dose. This applies to birth control pills and hormone replacement therapy.

— seizure medications that speed up the breakdown of thyroid hormones, potentially requiring a higher Westhroid dose.

— some SSRIs can affect thyroid hormone metabolism; monitoring TSH when starting or adjusting SSRIs is advisable.

— heart medication that is highly iodine-rich and can cause either hypothyroidism or hyperthyroidism; complex interaction with thyroid medications requiring specialist management.

Food and Supplement Interactions

— even plain coffee can significantly reduce Westhroid absorption. Wait at least 30–60 minutes after taking your dose before having coffee.

— separate from Westhroid by at least 4 hours.

— may reduce absorption; take Westhroid separately from high-soy or very high-fiber meals.

— some evidence suggests walnuts can reduce thyroid hormone absorption.

What to Tell Your Doctor Before Starting Westhroid

Before starting Westhroid, give your doctor a complete list of:

All prescription medications

Over-the-counter medications (antacids, iron, calcium)

Vitamins and supplements (especially iron, calcium, biotin, iodine)

Any history of heart disease, adrenal problems, or diabetes

For more on Westhroid side effects and what to watch for, see our Westhroid side effects guide.

Having trouble finding Westhroid at your pharmacy? medfinder can search nearby pharmacies to find which ones have it in stock.

Frequently Asked Questions

Yes, but not at the same time. Iron supplements significantly reduce the absorption of Westhroid. Separate your Westhroid dose from iron supplements by at least 4 hours. For most people, taking Westhroid first thing in the morning (before breakfast) and iron later in the day works well.

You should wait at least 30–60 minutes after taking Westhroid before drinking coffee. Studies have shown that coffee can significantly reduce thyroid hormone absorption, even when the tablet is swallowed before the first sip. Taking Westhroid first thing in the morning, then waiting before your coffee, is the standard recommendation.

Yes—this is an important interaction. Westhroid can increase the effects of warfarin (Coumadin), raising the risk of bleeding. If you take warfarin, your INR should be closely monitored when starting Westhroid or any time your dose changes. Tell your anticoagulation clinic or prescriber whenever your thyroid medication is changed.

Estrogen-containing birth control pills can increase thyroid-binding globulin, which means you may need a higher Westhroid dose to maintain the same thyroid hormone effect. If you start or stop hormonal contraception while on Westhroid, your TSH should be rechecked 6–8 weeks later.

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