Armour Thyroid is a natural desiccated thyroid medication used to treat hypothyroidism. Like all medications, it can cause side effects — some mild and temporary, others that need immediate medical attention. Here's what to expect and when to be concerned.

What Is Armour Thyroid?

Armour Thyroid is a prescription medication made from porcine (pig) thyroid glands. Unlike synthetic thyroid drugs like Synthroid (levothyroxine), Armour Thyroid contains both T4 and T3 hormones. It's manufactured by AbbVie and has been used for decades to treat underactive thyroid conditions. For a deeper look at how it works, see our guide on Armour Thyroid's mechanism of action.

Common Side Effects

Most side effects of Armour Thyroid happen when your dose is being adjusted or if the dose is slightly too high. Common side effects include:

• Temporary hair loss — This is one of the most reported side effects, especially in the first few months. It usually stops once your body adjusts.
• Headache
• Diarrhea or changes in bowel habits
• Changes in appetite — You may feel more or less hungry than usual.
• Nervousness or feeling jittery
• Increased sweating
• Sensitivity to heat
• Menstrual irregularities

These side effects are often signs that your dose may be slightly too high. If they persist for more than a couple of weeks, let your doctor know — a small dose adjustment usually helps.

Serious Side Effects — When to Call Your Doctor

Some side effects need immediate medical attention. Call your doctor or go to the emergency room if you experience:

• Chest pain or tightness
• Rapid or irregular heartbeat (pounding, racing, or skipping beats)
• Shortness of breath
• Seizures
• Severe tremors
• Rapid, unexplained weight loss
• Severe anxiety or panic attacks
• Signs of an allergic reaction — rash, hives, swelling of the face, lips, or throat, difficulty breathing

Important warning: Armour Thyroid carries a boxed warning stating that thyroid hormones should not be used for weight loss. Using doses higher than what your body needs can cause serious or life-threatening side effects, especially when combined with stimulant medications.

Side Effects in Specific Populations

Older Adults

Elderly patients are more sensitive to thyroid hormones. Even small dose increases can cause heart palpitations, chest pain, or worsening of heart conditions. Doctors typically start older adults on a lower dose (15 mg/day) and increase slowly.

Pregnant Women

Thyroid hormone needs often increase during pregnancy. Your doctor should monitor your TSH levels closely and adjust your Armour Thyroid dose as needed. Untreated hypothyroidism during pregnancy carries risks for both mother and baby.

People With Heart Disease

Patients with cardiovascular conditions need careful monitoring when taking Armour Thyroid. The T3 component acts faster than T4 and can stress the heart. Your doctor will start with a low dose and increase gradually.

People With Adrenal Insufficiency

If you have adrenal insufficiency, it must be treated before starting Armour Thyroid. Starting thyroid replacement without addressing adrenal function can trigger an adrenal crisis, which is a medical emergency.

How to Manage Side Effects

• Take it consistently. Take Armour Thyroid at the same time each day, on an empty stomach, 30 to 60 minutes before eating.
• Don't skip doses or double up. If you miss a dose, take it as soon as you remember — unless it's almost time for your next dose.
• Keep up with lab work. Regular thyroid panels (every 6-8 weeks during dose changes, then every 6-12 months) help your doctor keep your dose in the right range.
• Track your symptoms. Write down how you feel each day so you can share specifics with your doctor.
• Avoid interactions. Certain foods and medications can affect how your body absorbs Armour Thyroid. See our full guide on Armour Thyroid drug interactions.

Final Thoughts

Most people tolerate Armour Thyroid well, especially once they find the right dose. Mild side effects like temporary hair loss or jitteriness are common early on and usually resolve. Serious side effects are rare but important to know about.

If you're experiencing side effects, talk to your doctor before making any changes to your medication. And if you're having trouble finding Armour Thyroid at your pharmacy, Medfinder can help you locate it in stock near you.