Cytomel Interacts with More Medications Than You Might Think

Cytomel (Liothyronine Sodium) is a powerful thyroid hormone, and like most medications, it can interact with other drugs, supplements, and even certain foods. Some interactions reduce how well Cytomel works. Others increase your risk of side effects.

This guide covers the most important Cytomel drug interactions — what to avoid, what to watch for, and what to tell your doctor before you start treatment.

How Drug Interactions Work with Cytomel

Drug interactions with Cytomel generally fall into three categories:

1. Absorption blockers — Substances that physically bind to Cytomel in your digestive tract, preventing your body from absorbing it properly
2. Effect amplifiers — Medications whose effects increase (sometimes dangerously) when combined with thyroid hormones
3. Dose changers — Drugs that alter how much thyroid hormone your body needs, requiring a dose adjustment

Understanding which category an interaction falls into helps you know what to do about it — whether that's spacing out doses, adjusting amounts, or avoiding a combination altogether.

Medications That Interact with Cytomel

Major Interactions

These interactions carry significant risk and require careful monitoring or dose adjustments:

• Warfarin (Coumadin) — Cytomel increases the blood-thinning effect of Warfarin. This can raise your risk of bleeding. If you take both, your doctor will need to monitor your INR (a blood clotting measure) more frequently and may reduce your Warfarin dose.
• Insulin and oral diabetes medications — Thyroid hormones can raise blood sugar levels. If you have diabetes and start Cytomel, your Insulin or oral medication doses (like Metformin, Glipizide, or Glyburide) may need to be increased. Monitor your blood sugar closely during any thyroid medication changes.
• Sympathomimetic amines — These include medications like Pseudoephedrine (Sudafed), Ephedrine, and certain weight-loss drugs. Combining them with Cytomel increases the risk of heart problems, including rapid heartbeat and coronary insufficiency. This is part of the reason Cytomel carries an FDA boxed warning about not using thyroid hormones for weight loss.
• Digoxin (Lanoxin) — Cytomel can reduce Digoxin levels in your blood, making it less effective. Your doctor may need to increase your Digoxin dose and monitor your levels.
• Ketamine — Using Ketamine with Cytomel can cause dangerously high blood pressure and rapid heart rate. Make sure your anesthesiologist knows you take Cytomel before any procedure involving Ketamine.

Moderate Interactions

These interactions are manageable with awareness and proper timing:

• Cholestyramine (Questran) and Colestipol (Colestid) — These cholesterol-lowering medications bind to thyroid hormones in your gut, blocking absorption. Take Cytomel at least 4 hours apart from these medications.
• Oral contraceptives and estrogen therapy — Estrogen increases a protein called thyroid-binding globulin (TBG), which can lower the amount of free thyroid hormone available in your blood. If you start or stop estrogen-containing medications, your Cytomel dose may need adjustment.
• Antidepressants (TCAs and SSRIs) — Tricyclic antidepressants like Amitriptyline (Elavil) and SSRIs like Sertraline (Zoloft) or Fluoxetine (Prozac) may have enhanced effects when taken with Cytomel. Your doctor should monitor for increased side effects from either medication. Notably, Cytomel is sometimes used off-label to boost the effectiveness of antidepressants in treatment-resistant depression.
• Iron supplements — Iron binds to thyroid hormones and reduces absorption. Take Cytomel at least 4 hours apart from iron supplements (including prenatal vitamins containing iron).
• Calcium supplements — Like iron, calcium can interfere with Cytomel absorption. Separate by at least 4 hours.
• Proton pump inhibitors (PPIs) and antacids — Medications like Omeprazole (Prilosec), Esomeprazole (Nexium), and over-the-counter antacids like Tums or Maalox may reduce Cytomel absorption by altering stomach pH.

Supplements and OTC Medications to Watch

Several common supplements and over-the-counter products can affect Cytomel:

• Calcium supplements — Reduce absorption (take 4 hours apart)
• Iron supplements — Reduce absorption (take 4 hours apart)
• Multivitamins — Many contain calcium and iron (take 4 hours apart)
• Biotin (Vitamin B7) — While Biotin doesn't interact with Cytomel directly, high-dose Biotin supplements can interfere with thyroid lab tests, giving falsely abnormal results. Stop Biotin at least 48 hours before thyroid blood work.
• Decongestants containing Pseudoephedrine — Increases risk of heart-related side effects when combined with Cytomel

Food and Drink Interactions

What you eat and drink can affect how well Cytomel works:

• Take on an empty stomach — For best absorption, take Cytomel 30 to 60 minutes before eating. Food in general can slow down absorption.
• Soy products — Soy can interfere with thyroid hormone absorption. If you consume a lot of soy (tofu, soy milk, edamame), try to maintain a consistent intake rather than varying dramatically.
• High-fiber foods — A very high-fiber diet may reduce Cytomel absorption. Take your medication before meals, not with a high-fiber breakfast.
• Coffee — Coffee can reduce absorption if taken at the same time as Cytomel. Wait at least 30 to 60 minutes after taking your medication before having coffee.

What to Tell Your Doctor

Before starting Cytomel, give your doctor a complete list of everything you take, including:

• All prescription medications
• Over-the-counter drugs (pain relievers, cold medicines, antacids)
• Vitamins and supplements (especially calcium, iron, and Biotin)
• Herbal products

Also tell your doctor if you:

• Have diabetes (insulin or oral medication doses may need adjustment)
• Take blood thinners like Warfarin
• Take heart medications like Digoxin
• Are on estrogen or hormonal birth control
• Are pregnant or planning to become pregnant
• Have adrenal insufficiency

Any time you start, stop, or change the dose of another medication, let your prescribing doctor know — it may affect your Cytomel dose. For more on what Cytomel is and how it's used, see our complete Cytomel overview.

Final Thoughts

Cytomel is a safe and effective medication when used properly, but it does interact with a surprising number of common drugs, supplements, and foods. The most important rule: take Cytomel on an empty stomach, at least 4 hours apart from calcium, iron, and cholesterol-binding medications.

Keep your doctor informed about everything you take, and don't make changes to any medication without checking first. If you need help finding Cytomel at a pharmacy near you, Medfinder can show you where it's in stock.