Armour Thyroid vs. Synthroid: Differences, similarities & side effects

Key differences│Conditions treated│Insurance and cost│Side effects│Warnings│Bottom line

Armour Thyroid and Synthroid are both brand-name medications used to treat an underactive thyroid gland (hypothyroidism). They are part of the thyroid hormone drug class and work by supplementing thyroid hormones that are usually produced by the body. While both medications are known as thyroid agents, they have notable differences in chemical makeup and price.

Armour Thyroid vs. Synthroid: Key differences

Armour Thyroid and Synthroid are both thyroid hormone replacement medications, but they are biochemically different.

Amy Offutt, MD, president of the International Lyme and Associated Diseases Society (ILADS), and Inna Melamed, Pharm.D., a functional medicine practitioner and author of Digestive Reset, both sum up the differences:

• Armour Thyroid is a dried, animal-derived thyroid hormone (from pig thyroid glands), while Synthroid is a synthetic thyroid (synthetic T).
• Armour Thyroid contains triiodothyronine (T3) and thyroxine (T4), while Synthroid contains only T4.
• Armour Thyroid is only available as a brand-name drug, while Synthroid is just one brand-name version of the generic drug levothyroxine.

In addition to biochemical differences, Armour Thyroid costs more than Synthroid and tends to cause more side effects, according to Dr. Offutt. Dosing also differs dramatically between Armour Thyroid and Synthroid. Armour Thyroid is dosed in milligrams, which are thousandths of grams. Synthroid is dosed in micrograms, which are millionths of grams. 

Armour Thyroid vs. Synthroid: Conditions treated

Both Armour Thyroid and Synthroid are used to treat underactive thyroid, medically known as hypothyroidism. “Any patient who needs thyroid replacement hormone (because the thyroid is not secreting enough hormone naturally) can potentially benefit from Armour Thyroid or Synthroid,” Dr. Offutt says.

Armour Thyroid and Synthroid are used for hypothyroidism of all types:

• Primary hypothyroidism: When the thyroid gland itself does not secrete enough hormone
• Secondary hypothyroidism: When problems with the pituitary gland decrease thyroid activity
• Tertiary hypothyroidism: When disorders of the hypothalamus result in reduced thyroid activity

Armour Thyroid vs. Synthroid for Hashimoto’s  

Hashimoto thyroiditis is an autoimmune disease in which the body attacks its thyroid cells. This destruction of thyroid cells causes hypothyroidism.

“Either of these medications may be used to treat patients with hypothyroidism secondary to Hashimoto thyroiditis,” Dr. Offutt says. However, Dr. Melamed notes that the American Thyroid Association and other international organizations recommend Synthroid as the most effective option for Hashimoto’s-related hypothyroidism.

Is Armour Thyroid better than Synthroid?

Both Armour Thyroid and Synthroid are effective thyroid medications. They both replace thyroid hormones in patients whose thyroids do not secrete enough hormones naturally. Though Synthroid only has the T4 component of thyroid hormone, Dr. Offutt says it is believed that humans can convert some T4 to T3 after ingesting it. So, while Armour Thyroid offers a more complete hormone replacement, it is not always better. 

“The current conventional prescribing approach tends to be the prescription of levothyroxine (Synthroid),” Dr. Offutt says. However, she emphasizes the importance of a personalized approach and says that some patients may experience more improvement of symptoms with a T4 or T3 product like Armour Thyroid. 

In one retrospective study of 250 hypothyroid patients published in the Journal of the Endocrine Society, researchers found that patients tend to feel better when taking Armour Thyroid than when taking levothyroxine, but they also have a higher risk of adverse effects with Armour Thyroid than with levothyroxine. 

Ultimately, the most effective medication should be determined by a healthcare provider who has a complete picture of your medical condition, history, and other medications that you’re taking in order to see if they interact with Armour Thyroid or Synthroid.

Armour Thyroid vs. Synthroid: Insurance coverage and cost comparison

Without insurance, Armour Thyroid costs about $55 for 30, 60 mg tablets, while Synthroid costs about $76 for 30, 100 mcg tablets. However, drug prices vary widely. It’s a good idea to check with your insurance company or Medicare Part D plan for information that is accurate for your situation.

SingleCare coupons can help you save on Armour Thyroid, bringing the cost down to about $28 for 30, 60 mg tablets. You can also save on Synthroid, paying about $50 for 30, 50 mcg tablets.

Armour Thyroid vs. Synthroid side effects

Adverse reactions of both Armour Thyroid and Synthroid tend to be symptoms of thyroid problems rather than drug side effects. In other words, a person taking these drugs might experience symptoms of hyperthyroidism (if their dose is too high) or hypothyroidism (if their dose is too low). 

Common symptoms of imbalanced thyroid hormone include weight changes, hair loss, fast heart rate, and excessive sweating or nervousness. Side effects of Synthroid and Armour Thyroid are somewhat similar, with the exception of fatigue. In fact, 40.8% of patients in the study published by the Journal of the Endocrine Society switched from levothyroxine to Armour Thyroid because of the fatigue they experienced on levothyroxine.

Source: DailyMed (Synthroid/Armour Thyroid)

Synthroid & Armour Thyroid drug interactions

Drug interactions with Synthroid and Armour Thyroid tend to result in decreased thyroid hormone absorption. The interplay between drugs and hormones can be complicated, so it’s essential to seek medical advice from your healthcare provider or pharmacist if you are using Synthroid or Armour Thyroid along with other medications or supplements.

According to an observational study that included 10,999 patients, the most common drug interactions with Synthroid (levothyroxine) are iron, calcium, proton pump inhibitors, statins, and estrogens. These medications increase thyroid stimulating hormone (TSH), which helps regulate hormones made by the thyroid, in patients taking levothyroxine. Since these medications throw off the hormone balance, they may also interact with Armour Thyroid. 

According to the American Thyroid Association, thyroid hormone dosage may need to be adjusted for patients taking birth control pills, estrogen or testosterone, heart medications, anti-seizure medications, lithium, iron, calcium, and some cholesterol-lowering medications.

Synthroid & Armour Thyroid drug warnings

Synthroid and Armour Thyroid both have an FDA boxed warning (once known as a black box warning) advising against taking them for weight loss. Box warnings are the strongest safety-related warnings that alert healthcare providers and patients about dangerous uses and harmful effects.

Even when taken to supplement thyroid hormone levels, there are still serious possible side effects to be aware of. Severe diarrhea and intense sweating should be reported to a healthcare provider immediately. These are signs of hyperthyroidism—too much thyroid hormone due to overdosage. To prevent this, keep all appointments for blood tests that measure your hormone levels. 

Also, let your healthcare provider know if you are pregnant or breastfeeding. According to March of Dimes, Synthroid can be taken during pregnancy, but Armour Thyroid cannot.

Bottom line: Armour Thyroid vs. Synthroid 

Synthroid and Armour Thyroid are both intended to treat hypothyroidism. They replace thyroid hormones in patients whose thyroids do not secrete enough hormones naturally. 

Synthroid is a synthetic form of T4, while Armour Thyroid is an animal-derived form of T3 and T4. Both Synthroid and Armour Thyroid are brand-name drugs, but Synthroid is available in a generic form, which can be more affordable.

Both Synthroid and Armour Thyroid can be effective treatments for hypothyroidism. Only a healthcare provider with a complete picture of your health and medication list can recommend which one is better for you.